Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • 1990-1994  (801)
  • 1920-1924
  • 1991  (801)
  • Engineering  (596)
  • Physical Chemistry  (205)
  • 1
    Electronic Resource
    Electronic Resource
    Annotated bibliography of numerical modelling in electromagnetic compatibility (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 259-269 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents an annotated bibliography of numerical modelling in electromagnetic compatibility with emphasis on coupled transmission lines. Although the papers cited generally appeared in the open literature between 1980 and 1990, very useful works prior to that period are covered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040311
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Calculation of radiated electromagnetic fields from electronic systems (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 241-258 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The electromagnetic radiation from electronic systems is formulated in terms of an integral equation for the electric and the equivalent magnetic current density, which is numerically solved by the method of moments. The electromagnetic coupling to conducting thin wires, thin plates, and aperture fitted cabinets is taken into account by appropriate operator equations.In order to solve the integral equation of electrically large conducting structures, suitable basis functions are needed to minimize the computation time. B-spline functions of the second and third degree are used as a basis in the moment method, which lead to a decrease of the computation time.A second way to decrease the computation time is given by the possibility of determining which parts of the structure of a printed circuit board (PCB) have to be considered and which parts can be neglected. Examples show that the influence of near source conducting areas to the radiated emissions is strong. It will be shown that this influence depends on the geometrical symmetry, the shape, and the distance of the scattering body.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040310
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Editorial (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 1-1 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040102
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991) 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040101
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Radiation losses in microstrip antenna feed networks printed on multilayer substratesInvited Paper. (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 3-18 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The effect of the substrate structure on the radiation properties of microstrip array feed networks is investigated with the space-domain integral equation approach. Numerical and analytical techniques are employed to produce efficient computer algorithms. Results for space and surface wave losses are presented for corner discontinuities printed on substrate/superstrate, and two-layer substrate structures. Comparisons are made with the single-layer case.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040103
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Comprehensive MoL analysis of a class of semiconductor-based transmission lines suitable for microwave and optoelectronic applicationInvited Paper. (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 45-62 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A comprehensive analysis procedure is presented to investigate mode propagation in a class of semiconductor-based transmission lines suitable for application in microwave or optoelectronic circuits. The method of lines (MoL) has been used to investigate single or multiconductor planar transmission line structures printed on a combination of insulating and semiconducting substrate. Homogeneous as well as inhomogeneous doping areas in the semiconductor are included in the theoretical formulation. Numerical results are presented for III-V semiconductor travelling wave electro-optic modulators in double-rib, multilayer strip waveguide configuration, microslabTM transmission lines with partial and full strip cover and slow-wave MIS microstrip/coplanar transmission lines on thick and thin film semiconductor substrate with gradually inhomogeneous doping layer.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040105
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Editorial (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. i 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040202
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991) 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040301
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Solving the helmholtz equation using multiply propagated fields (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 123-138 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Computer models in electromagnetics are based primarily either on integral or on differential equations. The former arise from source integrals using some appropriate Green's function whereas the latter originate from the Maxwell curl equations. Although requiring volume rather than surface sampling even for spatially homogeneous problems, in contrast to integral-equation (IE) models, differential-equation (DE) models are geneally a better choice for problems involving spatial inhomogeneities. This is because such problems require volumetric sampling using either approach, but the DE model produces a sparse matrix rather than the full matrix of the IE formulation.In this paper we describe a new approach based on using multiply propagated fields for numerically solving the banded matrix that results from discretizing the Helmholtz equation. A computer-time savings of N1/2 and N2/3 for two-dimensional (2-D) and three-dimensional (3-D) problems, respectively, is made possible, where N is the total number of field samples or unknowns. For even moderate-size problems where 100 samples per linear dimension are used (N2 = 10,000 and N3 = 1,000,000), the time savings can be of the order of 100 and 10,000 respectively. Another advantage of this procedure, which we call Helmholtz equation multiple propagator (HEMP), is that the radiation or closure condition needed to terminate the spatial solution mesh for exterior problems can be enforced rigorously with essentially no additional computational cost.The method is illustrated for a 2-D problem by application to plane-wave scattering from an infinite, metal, circular cylinder. Results are presented for the mode amplitudes of the scattered field, the induced surface current, and the bistatic far field as obtained from HEMP, and shown to be in good agreement with the analytical results. Although limited here to the simplest possible application in order to establish its feasibility, the approach's advantage would be its applicability to 2-D and 3-D problems involving inhomogeneous, penetrable objects.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040207
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Time-domain integral equations for EMP analysis (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 153-162 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Two computer programs DOTIG1 and DOTIG2 were developed to calculate, in the time-domain, the interaction of transient electromagnetic pulses (EMP) with perfect electric conductor structures modelled by thin wires (DOTIG1) or patches (DOTIG2). DOTIG1 uses the electric field integral equation and DOTIG2 the magnetic field integral equation. Briefly described below are the numerical procedures used to develop both programs and some results that show their characteristics.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040304
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 11
    Electronic Resource
    Electronic Resource
    Time-domain calculation of electromagnetic plane-wave induced surges on overhead transmission lines (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 189-201 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper presents a time-domain method to calculate electromagnetic plane wave induced surges on overhead multiconductor transmission lines. By means of some particular line impulse responses, the method takes into account the distributed nature of the coupling with plane wave radiated fields. A comparison of measured plane-wave induced voltages reported in the literature and calculated voltages shows a very close agreement.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040307
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 12
    Electronic Resource
    Electronic Resource
    Propagation of picosecond pulses in superconducting microstrip interconnections on integrated circuits (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 203-223 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Studies on the propagation of picosecond pulses in coupled microstrip line interconnections on silicon integrated circuit substrates are presented. The effects of conductor and dielectric losses in the transmission line on the distortion, delay and attenuation of picosecond pulses are studied in detail. A direct comparison is made with the propagation characteristics of interconnects using ordinary metals and high-temperature superconductors such as YBa2Cu3O7. The results generally show the advantages of using high-temperature superconductor tracks on low-loss integrated circuit substrates such as GaAs. However, even in this case, geometrical dispersion can cause distortion on the pulses and it is therefore an important factor to be considered.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040308
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 13
    Electronic Resource
    Electronic Resource
    An investigation of the numerical properties of the mode-matching techniqueInvited Paper. (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 19-43 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A new insight into the numerical properties of the mode-matching (MM) technique is given at the example of capacitive and inductive diaphragms in rectangular waveguide. The presence of two sources of error is pointed out and the existence is demonstrated of an optimum modal ratio which produces the best compensation between the two errors. The MM technique is formulated in a generalized form as an integral equation for either the electric field on the aperture or the current on the diaphragm. This allows the edge condition to be incorporated into the basis functions in order to improve the numerical efficiency of the method. An extensive investigation of the numerical properties of the various formulations in different cases is presented, including the frequency behaviour of the numerical error.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040104
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 14
    Electronic Resource
    Electronic Resource
    Comparison between different formulations of the transverse resonance field-matching technique for the three-dimensional analysis of metal-finned waveguide resonatorsInvited Paper. (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 63-73 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Two different formulations of the transverse resonance field-matching technique are applied to evaluate the modal spectrum of metal-finned waveguide structures. In the theoretical treatment, Method 1 uses boundary conditions prior to interface relations and allows the number of expansion terms to be selected according to the dimensions of the cross-section subregions. Method 2 imposes boundary and interface conditions in reversed order but requires the same number of expansion terms to be used in various subregions. The two procedures are then compared with respect to their influence on the modal scattering matrix computation of metal-finned waveguide resonators. Method 2 shows excellent agreement with measurements, but it is restricted to configurations with relatively thin fins and moderate slot widths. Although Method 1 may be applied to more general structures, this procedure requires a higher computational effort and leads to slightly different results. However, it constitutes a powerful PC-operational alternative whenever an extended precision compiler, as required for Method 2, is not available.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040106
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 15
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991) 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040201
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 16
    Electronic Resource
    Electronic Resource
    A convergence index for field solutions in nonlinear media (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 75-80 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040203
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 17
    Electronic Resource
    Electronic Resource
    Concurrent processing applied to the Exodus Monte Carlo technique (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 97-105 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: This paper illustrates how problems based on the Probabilistic Potential Method can be solved using a parallelized form of the Exodus Monte Carlo technique. The Exodus technique which does not use random number generation is shown to be more efficient for moderately large problems than the conventional fixed random walk method when programmed in both sequential and concurrent forms.The technique is illustrated for an electrostatic field problem by using as an example internal potential evaluation for a rectangular coaxial line. The problem geometry is torn into subsections which are then analysed independently using concurrent programming methods. The resulting algorithm is compared with the same problem executed using a conventional sequential algorithm. Computation is achieved by use of an array of transputers. The design of the concurrent algorithm is described in detail and typical results are compared with the fixed random walk Monte Carlo method and also with the finite difference relaxation method. Parallel Fortran is used throughout as the programming language.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040205
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 18
    Electronic Resource
    Electronic Resource
    Call for papers (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 139-139 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040208
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 19
    Electronic Resource
    Electronic Resource
    An efficient velocity-space model of carrier transport in Gallium Arsenide (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 301-320 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A new GaAs carrier transport modelling methodology is presented, designed to address the competing needs of microscopic detail and of computational efficiency. The rationale for advanced semiclassical models based on the Boltzmann transport equation (BTE) are reviewed and discussed in terms of the unique properties of GaAs. A new methodology is then presented, formulated around a one-dimensional velocity-space variable. It includes a realistic description of the GaAs band structure including multiple valleys, non-parabolicity, and anisotropy, which is used to explicitly evaluate the scattering distributions, and rates, for different scattering mechanisms. These in turn allow a direct evaluation of the BTE scattering inegral, which is solved iteratively with the non-scattering terms. Based on this methodology, a prototype model is shown to reproduce the GaAs velocity-field relationship in homogeneous, undoped material. Band structure and forward-scattering effects are clearly visible in the model's solutions for the carrier velocity distribution. The model's computational simplicity, combined with a finer level of detail, makes it suitable for device simulation without invoking Monte Carlo or other computationally intensive methods.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040405
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 20
    Electronic Resource
    Electronic Resource
    Call for Papers (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 271-271 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040312
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 21
    Electronic Resource
    Electronic Resource
    Analysis of cross-talk on high-speed digital circuits using the finite difference time-domain method (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 225-240 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Cross-talk and pulse distortion in high-speed digital circuits have long been major design considerations. With the present trend towards increased speed and packing density the commonly used TEM approximation is no longer capable of producing sufficiently accurate results. In this contribution, the finite-difference time- domain technique incorporating a novel means of launching the pulses is used to provide a rigorous three- dimensional simulation of cross-talk on high-speed digital circuits. This includes the often-neglected effects of higher-order modes and surface waves. Results are presented for pulses propagating along a single track and for coupling between two and three tracks using square, gaussian and raised cosine pulse excitation functions. The results are shown to be in good agreement with other rigorous analyses.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040309
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 22
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991) 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040401
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 23
    Electronic Resource
    Electronic Resource
    Improvements in the analysis of a TH0mp cavity for precise complex permittivity measurements (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 273-286 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: An analysis of the relationship between complex permittivity and complex resonance frequency is proposed for a cylindrical cavity oscillating in a TM0mp mode. Effects of wall conductivity, coupling loops, and holes for the insertion of dielectric samples are fully taken into account. With dielectric samples of small radii, insertion holes produce the most important corrections. Their effect is modelled through a finite difference solution of the field equations in the neighbourhood of the holes. A computer program is described for the analysis, the use of which is illustrated with results of measurements.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040403
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 24
    Electronic Resource
    Electronic Resource
    Numerical modelling of microwave detectors at high signal level (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 321-328 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The relationship between microwave power absorbed by a detector diode and the resulting detected voltage at high signal level is investigated. Experimental data is obtained from a zero-biased diode mounted in a rectangular waveguide system operating at 9.5 GHz. The Alpa Industries Inc. 4561, 6724 and 6725 Schottky diodes and the M/A-COM 1N23 Point Contact diode with 1 kω and 106 kω loads are examined. The P-V relationships are analysed by solving a system of non-linear differential equations based on a lumped parameter model of the microwave system and diode.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040406
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 25
    Electronic Resource
    Electronic Resource
    Editorial (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. ii 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040402
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 26
    Electronic Resource
    Electronic Resource
    Electromagnetic scattering from conductor-coated material bodies (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 287-299 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A moment method solution is presented to compute electromagnetic scattering from material bodies. The bodies are supposed to be homogeneous, arbitrarily shaped and lossy; they can be coated with very thin perfect conductors in some parts. A formulation of the scattering problem is made in terms of the equivalent surface current densities for which mixed potentials are used. The equivalent currents are expanded in the space-domain by a triangular expansion function on the triangulated surfaces of the scatterer. The Galerkin procedure is carried out to test boundary integral equations and reduce the functional form of the equations to a partitioned matrix equation. The solution is applied to the scattering problem of a dielectric slab, a thin conductor coated by absorber material and a rectangular patch on a grounded dielectric slab. The computed backscattering radar cross-section and surface current densities of the structures are presented and some of the results are compared with experimental data.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040404
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 27
    Electronic Resource
    Electronic Resource
    Adaptive refinement in 2-D finite element applications (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 81-95 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: An adaptive mesh refinement scheme in the finite element method is presented in this paper. The new criterion Bdiff for adaptive refinement is tested for its validity. A technique for approximating curved boundaries employing the concept of triangle subdivision in conjunction with Delauney triangulation is also considered, so that the mesh produced is optimal. The implementation of the adaptive mesh refinement criterion in conjunction with the proposed technique of including the curved boundaries in the finite element model is described in detail and several examples of its application are given by way of illustration.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040204
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 28
    Electronic Resource
    Electronic Resource
    The modified semiconductor equations and associated algorithms for physical simulation (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 107-122 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: A set of modified semiconductor equations is described together with novel algorithms for solving them. These ensure a well-behaved, guaranteed convergent solution for a steady-state semiconductor model. Examples results on the simulation of a GaAs Dual Gate MESFET are given to demonstrate the efficiency of the new scheme.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040206
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 29
    Electronic Resource
    Electronic Resource
    Editorial (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 141-141 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040302
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 30
    Electronic Resource
    Electronic Resource
    Transmission-line modelling in electromagnetic compatibility studies (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 143-152 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The transmission-line modelling (TLM) method is applied to problems in electromagnetic compatibility (EMC). Simulated results for a field-to-wire coupling problem are presented, together with comparisons with experimental results. The comparisons confirm the validity of the model and its accuracy. The effects on resonances and field profiles, of placing a measurement dipole antenna inside a screened room are investigated. The resonant structure inside an unlined screened room and the same room when lined with radiation-absorbing material are investigated using a TLM model. The results confirm that the model developed can be used for the characterization of the entire EMC test environment.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040303
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 31
    Electronic Resource
    Electronic Resource
    Modelling of electromagnetic wave penetration through loaded apertures (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 163-174 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Calculation of the electromagnetic field diffracted by an aperture situated in a perfectly conducting ground plane can be made through the well-known theory of polarizabilities. However, simple expressions are only obtained under conditions which are not often fulfilled in electromagnetic compatibility problems since, for example, the disturbing field incident on the aperture must be considered as a uniform one. Furthermore, if the aperture is loaded by a low conducting material, available approximate formulas are only valid for a small circular hole. In this paper, we present a numerical approach based on the determination of the equivalent magnetic current distributed on the surface of the aperture. This distribution is the solution of an integral equation solved by the method of moments. This formulation allows us to take the surface impedance of a loading material and the contact resistance between this material and the rim into account. The validation of the computer code is shown by comparing computed and analytical results on some typical examples. Few applications are also described.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040305
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 32
    Electronic Resource
    Electronic Resource
    Computation of the electromagnetic field distribution inside enclosures with apertures using 3-D FEM (1991)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 4 (1991), S. 175-188 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Knowledge of the electromagnetic field distribution inside electronic enclosures due to incident fields is of interest to EMC design engineers. In this paper, a three-dimensional formulation of the finite element method was developed to solve the electromagnetic field distribution inside metal enclosures with apertures. The formulation was developed using a three-component vector magnetic potential and a scalar electric potential. The displacement current as well as the conduction current term was included. The region of interest was discretized using eight-node isoparametric hexahedrons and the potential functions were defined using linear first-order basis functions. The penetration of a steady-state electromagnetic field through an aperture into a simple cavity was analysed with the 3-D FEM program.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660040306
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 33
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040101
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 34
    Electronic Resource
    Electronic Resource
    Geometry of 2-benzopyrylium and pyrylium cations calculated by semi-empirical methods. Crystal and molecular structure of 1,3-dimethyl-6,7-dimethoxy-2-benzopyrylium perchlorate (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 7-12 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: X-ray data on the crystal and molecular structure of 1,3-dimethyl-6,7- dimethoxy-2-benzopyrylium perchlorate show a good correlation with the geometry of the same cation calculated by the MINDO/3 and MNDO methods with total optimization of all geometrical parameters. The geometry of substituted pyrylium cations was determined by the MNDO and AM1 methods. On the basis of the data obtained, some effects of benzo [c] annelation are displayed for the 2-benzopyrylium cation in comparison with the pyrylium cation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040103
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 35
    Electronic Resource
    Electronic Resource
    Micellar catalysis of the intramolecular aminolysis of the β-lactam antibiotic cephaclor (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 19-24 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rate of intramolecular degradation of cephaclor, involving the attack of the amino group at C-17 (N-18) on the β-lactam carbonyl, was increased up to 50-fold by neutral (polyoxyethylene-23 lauryl ether; Brij) and zwitterionic [3-(N-dodecyl-N, N-dimethylammonium) propane 1-sulphonate; (SDP)] micelles. The rate of OH- attack on cephaclor was increased 2-3-fold by Brij and SDP micelles. In the absence of micelles the rate of intramolecular degradation of cephaclor increased by up to 2-fold by addition of organic solvents. Distance calculations, based on the crystal structure of the antibiotic, showed that the intramolecular degration can only proceed in a conformation involving a cis-amide bond (N-14 - C-15). Micellar catalysis of the intramolecular degradation process was proposed to be due to the stabilization of the reactive conformation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040105
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 36
    Electronic Resource
    Electronic Resource
    Development of a model to explain the influence of the solvent on the rate and selectivity of diels-alder reactions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 48-52 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvophobic and polarity parameters are used to explain the endo/exo selectivity of the reaction between cyclopentadiene and methyl acrylate. A good linear regression model with Sp and ETN is obtained. The existence of an intrinsic correlation between the Sp and ETN values, which makes the interpretation of the results difficult, is shown. A comparison of the results with other previously reported showed that the relative influence of Sp and ETN on selectivity depends on the nature of the reagents.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040108
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 37
    Electronic Resource
    Electronic Resource
    Aggregation of amphiphilic molecules in water. I. α-phenylethylamine: 1H and 13C NMR study (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 58-66 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The concentration dependence of the 1H and 13C NMR chemical shifts in D2O and in CDCl3 solutions were determined for (±)-α-phenylethylamine (I). Aqueous solutions of (-)-I and (+)-I, 50% enantiomerically enriched in (-)- and (±)-2, 2, 2,-trifluoro-1-phenylethanol and the (+)- and (-)-N-formyl derivatives of I, were also studied. 1H nuclear Overhauser enhancements were used to check the conformations of the solutes at various concentrations and 1H T1 values were used to monitor the changes in molecular tumbling in solutions. The results are interpreted in terms of a spontaneous aggregation of solute molecules in water, with the possible determination of the critical micelle concentration. The time-dependent splittings in the 1H NMR spectra suggest further, more detailed, studies of the structures of the aggregates and the possibility of chiral recognition in water.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040110
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 38
    Electronic Resource
    Electronic Resource
    Evaluation of solvent effects on the dissociation of aliphatic carboxylic acids in aqueous N,N-dimethylformamide mixtures according to the scaled particle theory (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 87-95 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The standard Gibbs energies of transfer, ΔGt° from water to water-N,N-dimethylformamide mixtures for the dissociation process of several organic acids (formic, acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, 2-methylbutyric and trimethylacetic acids) obtained from the pKa* values are discussed in terms of the extended Scaled Particle Theory from quantum mechanical calculations in order to estimate the cavity and electrostatic contributions. The residual energy term was correlated with the hydrogen bond acceptor density and the Kamlet-Taft β parameters. The main contribution to ΔGt° was due to dipolar and specific interactions.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040204
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 39
    Electronic Resource
    Electronic Resource
    The 11C/14C kinetic isotope effect method. The 11C/14C kinetic isotope effect in the SN2 reaction of N,N-dimethyl-p-toluidine with labelled methyl iodide (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 77-86 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Methodological aspects of the determination of 11C/14C kinetic isotope effects (KIEs) were investigated using the reaction of N, N-dimethyl-p-toluidine with labelled methyl iodide in methanol at 30 °C as model system. The primary 11C KIE was determined to be 1.202 ± 0.008 for this reaction. The isotope effect was determined by a one-pot technique based on liquid chromatographic fractionation of the reactant and product followed by liquid scintillation counting of the 11C and 14C radioactivity in these fractions. The KIE value obtained agrees well with the value predicted from a previously determined 12C/14C-KIE for the same reaction. Theoretical model calculations of both carbon KIEs were performed using the BEBOVIB IV program. Transition-state models ranging from reactant- to product-like were employed in the calculations, and three different reaction coordinate models with more or less pronounced Walden inversion of the methyl hydrogens were investigated.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040203
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 40
    Electronic Resource
    Electronic Resource
    Cross-interaction constants as a measure of the transition state structure. Part 15. Kinetic isotope effects in the SN2 reactions of 2-phenylethyl derivatives with deuterated aniline nucleophiles (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 101-106 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic isotope effects (KIE) were determined for the reactions of 2-phenylethyl and 1-methyl-2-phenylethyl benzenesulphonates with deuterated aniline nucleophiles in acetonitrile at 65.0 °C. The results are in good agreement with the transition state (TS) structures proposed based on the sign and magnitude of the cross-interaction constants, pxz, between the substituents in the nucleophile (X) and the leaving group (Z). In the reactions of 2-phenylethyl derivatives, all three reaction pathways, kr, kt and kΔ, were found to be contributing competitively; the inverse secondary KIE observed with a stronger nucleophile changed into the primary KIE with a weaker nucleophile owing to the predominant contribution of the four-centre TS in the kf path. For the reactions of the 1-methyl-2-phenylethyl series, the kr path played a major role, the contribution from the front-side nucleophilic attack, kf, being negligible. In both reaction series, the aryl participation was important for the p-CH3O-substituted substrate.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040206
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 41
    Electronic Resource
    Electronic Resource
    Addition of hydroxylamine to cyclohexanone and bicyclic ketones. Steric, electronic and hydrogen bonding effects on the general mechanism of addition of amines to carbonyl compounds (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 107-112 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Three different types of pH-rate profiles were observed for the addition of amines to carbonyl compounds, depending on the relative predominance, at weakly acidic pH, of either a concerted or a stepwise mechanism. The predominant mechanism depends on the basicity of the amine and the mutual equilibrium affinity for adduct formation between the carbonyl compound and the amine. The reaction of hydroxylamine with cyclohexanone and bicyclic ketones was studied in order to examine the roles of steric and electronic effects in this mechanism. Cyclohexanone and 3-chlorobicyclo [2.2.1] heptan-2-one exhibit the profile expected for a single change in the rate-determining step with increasing pH from uncatalysed attack of the amine on the carbonyl group to hydronium ion-catalysed dehydration of the carbinolamine. In contrast, both bicyclo [2.2.1] heptan-2-one and bicyclo [2.2.2] octan-2-one show an unexpected profile with two negative breaks and five kinetically significant regions. This profile is explained by stabilization of the zwitterionic intermediate T± by intramolecular hydrogen bonding, leading to the formation of the carbinolamine by a stepwise mechanism at weakly acidic pH.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040207
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 42
    Electronic Resource
    Electronic Resource
    Crystal and molecular structure of pyrylium salts. IV. Crystal and molecular structure of 2,6-diphenyl-4-(4-carboxyphenyl)pyrylium perchlorate. Interrelations between structural parameters due to substituent effects (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 121-124 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal and molecular structure of 2,6-diphenyl-4-(4-carboxyphenyl)pyrylium perchlorate was solved by x-ray diffraction, yielding structural parameters of high precision (estimated standard deviations for bond length ≤ 0.5 pm, for bond angles ≤ 0.2°). Comparison with other 4-substituted derivatives of 2,6-diphenyl-4(4-carboxytphenylpyrylium) perchlorate shows regularities in the variations of structural parameters following classical views of substituent effects.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040209
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 43
    Electronic Resource
    Electronic Resource
    Structure and dynamics of dicyandiamide: A theoretical study (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 125-134 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio MO methods have been used to study the structures and energetics of dicyandiamide, [(NH2)2C=N—C≡N], its isomers, protonated species, radical anions, transition structures for internal conformational change and transition structures for isomerization. Structures were optimized at the HF/STO-3G, HF/3-21G and HF/6-31G* levels; selected barrier heights for smaller analogues were also computed at the MP4SDTQ/6-31G* level. The most stable isomer of dicyandiamide has the cyano group on the imine nitrogen [1, (NH2)2C=NC≡N]; the other isomer [2, HN=C(NH2)NH—C≡N] lies 12.8 kcal mol-1 higher. Inversion at the imino nitrogen proceeds by a linear, in plane process with a barrier of 32.5 kcal mol-1. The amino rotation barriers are 19 kcal mol-1 (single NH2) and 40 kcal mol-1 (both NH2 in a conrotaory or a disrotatory fashion; if the NH2 groups are allowed to pyramidalize the disrotatory barrier drops to 20 kcal mol)-1. Protonation occurs preferentially on the imine nitrogen (PA = 219.7 kcal mol-1 for 1); the proton affinities PA of the amino nitrogens are 25-30 kcal mol-1 lower. Isomerization between 2 and 1 would go via a 1,3-sigmatropic hydrogen shift, but the barrier is high (48.3 kcal mol-1); protonation reduces the hydrogen shift barrier by ca 15 kcal mol-1. However, the most likely mechanism for isomerization involves protonation of the imine nitrogen in 2 followed by deprotonation of the cyano-substituted nitrogen to form 1, circumventing the energetically costly 1,3-sigmatropic hydrogen shift. When an electron is transferred to dicyandiamide, a sizeable fraction of the resonance stabilization of the guanidine moiety is lost.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040302
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 44
    Electronic Resource
    Electronic Resource
    The grignard reaction of α-diketones. Radical intermediates as the determinant of carbon- and oxygen-attacked products (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 158-162 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Although carbon (normal)- and oxygen (abnormal)-attacked products are usually afforded in the Grignard reaction of α-diketones, the relative ratio of the two are strongly dependent on the structure of the Grignard reagents. The product-determining factors are discussed on the basis of the intermediate radicals formed from α-diketones and Grignard reagents.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040306
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 45
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040401
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 46
    Electronic Resource
    Electronic Resource
    Kinetics of oxidation of hydrocarbons by quinolinium dichromate (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 217-224 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Quinolinium dichromate (QDC) oxidizes hydrocarbons (toluenes and phenanthrenes) smoothly in dimethylformamide in the presence of acid. The rate of the reaction was first order in each substrate, oxidant and acid. The effects of variations in solvent composition and temperature were studied. The rate data obeyed Hammett's relationship and the values of ρ were -0.20 for toluenes and -1.79 for phenanthrenes. Induced polymerization of acrylonitrile and the reduction of mercury(II) chloride were not observed. For the oxidation of toluenes, a kinetic isotope effect, kH/kD = 5.13, was observed. The initial reaction for the oxidation of toluenes involved hydrogen abstraction, forming an intermediate which was rapidly converted to the product, the corresponding aldehyde. For the oxidation of phenanthrene, the experimental data have been rationalized in terms of a hydride ion transfer in the ratedetermining step.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040404
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 47
    Electronic Resource
    Electronic Resource
    Isotope effects in acid-catalyzed aromatic hydrogen exchangePresented in part at the 68th CIC Chemical Conference, Kingston, Canada, June 1985, paper no. OR-C3-4. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 233-241 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Deuterium- or tritium-substituted aromatics undergo isotope exchange in fairly concentrated aqueous sulfuric acid media. The rate constant for this process is complex, being composed of that for the slow electrophilic attack, and the isotope effect on the breakup of the Wheland intermediate. Using experimental rate constant data for both deuterium and tritium exchange on the same substrate, the excess acidity method and the Swain-Schaad relationship, true protonation rate constants and isotope effects have been separated out for several positions in several simple aromatic substrates. Most of the electrophilic attack rate constants are described by a Hammett-type linear free energy relationship with a ρ+ of - 6.5. The average observed deuterium isotope effect on Wheland intermediate breakup was 5.3. Using rate constants obtained at different temperatures, enthalpies and entropies of activation were also obtained for benzene, naphthalene and thiophene; the activation entropy averaged - 8 cal mol-1 K-1. Some evidence was found for general acid catalysis at the higher acidities.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040406
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 48
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040501
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 49
    Electronic Resource
    Electronic Resource
    Conversion of flavanones into chalcones in alkaline medium. Kinetic and spectroscopic studies (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 263-270 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The conversion of flavanone and 7-hydroxyflavanone in alkaline water and heavy water and of the same compounds and of 4′ -nitroflavanone in alkali-methanolic media into the corresponding substituted chalcones was studied kinetically and spectroscopically. Treatment of kinetic data in this work and data for the reverse reaction determined previously allowed the estimation of the partial rate coefficients for each step and of the free-energy changes for the three systems studied. To disentangle isotope effects, the conversion of [3-D2]-flavanone was also studied. The present results confirm a previously suggested mechanism for the spontaneous reaction and afford essential information that may contribute to a more detailed understanding of the mechanism of the enzyme-catalysed reaction.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040502
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 50
    Electronic Resource
    Electronic Resource
    Kinetic modelling of the low-temperature photo-oxidation of hexafluoropropene (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 293-300 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: By kinetic simulation, the significant features of the mechanism of the low-temperature photo-oxidation of hexafluoropropene were elucidated and the rate constants for the major elementary reactions of the intermediate fluorinated peroxy and alkoxy radicals were determined through a best-fit procedure. Comparison with analogue reactions in non-fluorinated systems showed a significant increase in reactivity for the self-reaction and double bond addition by peroxy radicals and β-scission by alkoxy radicals, which are discussed in terms of fluorine substituent effects.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040506
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 51
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040601
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 52
    Electronic Resource
    Electronic Resource
    New ideas on phase transfer catalysts: SN2 reaction with a solid ionophoric salt (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 336-340 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new mechanism of substitution between n-hexyl bromide (RBr) and solid potassium chloride in toluene under phasetransfer catalysis conditions is suggested, involving the formation of intermediates, adsorbed on the solid phase, viz., two binary (KCl·QX and KX·QBr) and two ternary (QX·KCl·RBr and QBr·KX·RCl) complexes. According to this mechanism, the catalytic activity of onium salts (QX) in the substitution changes in the order QI 〉 QBr 〉 QCl. The nature of the catalyst cation has little or no effect on the reaction rate. A general rule is proposed according to which in this reaction the substrate is attacked by a stronger nucleophile whereas a weaker nucleophile accepts the leaving group of the substrate. These and earlier data are interpreted in term of the SN2 process occurring on the solid-phase surface. The structure of the ternary complexes and the role of the phase-transfer catalyst are discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040603
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 53
    Electronic Resource
    Electronic Resource
    Origin of apparent swain-schaad deviations in criteria for tunneling (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 361-366 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vibrational analysis calculations have been conducted in an effort to understand the origins of apparently anomalous relationships reported between kH/kT and kD/kT kinetic isotope effects. The actual isotopic substitutions used in previous work are more complex than a simple comparison between H/T and D/T isotope effects. The relationships between the actual isotope effects determined in these studies amount to tests of two standards of conventional isotope effect theory, the rule of the geometric mean (or the lack of isotope effects on isotope effects) and the Swain - Schaad rule. Model calculations illustrate the importance of violations of the rule of the geometric mean (over Swain - Schaad deviations) arising in models that incorporate both explicit reaction-coordinate coupling of two isotopic sites and reaction-coordinate tunneling. Implications for experimental studies of turneling using apparent Swain - Schaad exponents are discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040607
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 54
    Electronic Resource
    Electronic Resource
    The schiff base between pyridoxal-5′-phosphate (PLP) and hexylamine. Formation of the unprotonated form of the imine by reaction of the unprotonated PLP and free amine (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 372-380 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Electrochemical and spectrophotometric studies of the pyridoxal-5′ -phosphate hexylamine Schiff base (PHSB) in strongly basic media were carried out. The equilibrium constant and rate constants of the formation and hydrolysis of the unprotonated imine from the unprotonated pyridoxal-5′ -phosphate and free amine were determined by linearscan cyclic voltammetry. The acid-base dissociation constant of the imine group was obtained by spectrophotometric measurements. Absorption bands for the free imine and the conjugate acid are characterized by a log-normal distribution. These studies are for general application to the quantitative characterization of non-enzymatic model compounds.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040609
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 55
    Electronic Resource
    Electronic Resource
    Factors affecting the reversibility of the electrophilic step in olefin bromination. The case of 5H-dibenzo [a, d] cycloheptene (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 387-398 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The tendency of ion-pair intermediates generated by treatment of trans-10-bromo-10, 11-dihydro-11-hydroxy-5H-dibenzo [a, d] cycloheptene (5) with HBr to release Br2 giving 5H-dibenzo [a, d,] cycloheptene (1) has been evaluated. The observed 9:1 ratio between ion-pair collapse to the trans-dibromide (7) and Br2 release to olefin 1, as compared with the 3:7 ratio found with the 5H-dibenz [b, f] azepine-5-carbonyl chloride system, has been interpreted as indicating a much lower propensity for reversibility of ion-pair formation in the bromination of 1. The structural parameters obtained by x-ray diffraction of the dibromide 7 show for this compound an angle strain at C-10 and C-11 analogous to that found in trans-10, 11-dibromo-10, 11-dihydro-5H-dibenz [b, f,] azepine-5-carbonyl chloride. Olefin 1 adds Br2 in 1,2-dichloroethane at 25°C according to a third-order rate law, with k3 = 30(3) M-2 s-1. About 10% of 5-bromo-5H,-dibenzo [a, d] cycloheptene, arising from collapse of a dibenzo [a, d] tropylium ion intermediate (9), is formed in this reaction besides the expected trans-dibromide 7. Spectral evidence for the formation of 9, arising by rearrangement of a first formed weakly bridged ionic intermediate in the reaction of 1 with Br2, is presented. the results obtained with the 5H-dibenzo [a, d,] cycloheptene system have been rationalized on the basis of the formation of very weakly bridged intermediates having a much lower tendency to revert back to olefin and Br2 with respect to the corresponding symmetrically bridged bromonium ions.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040611
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 56
    Electronic Resource
    Electronic Resource
    SRN1 Reactions of nucleophiles with radical clocks: Rate constants for some radical-nucleophile reactions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 404-412 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Treatment of o-3-(but-3-enyloxy)benzene (1) with anions -SPh, -PPh2 and -PO(OEt)2 in ammonia, acetonitrile or dimethyl sulphoxide gives both direct substitution and cyclized products. The formation of the latter confirms the intermediacy of the o-3-(but-3-enyloxy)phenyl radical (2) and confirms that the reactions follow the SRN1 pathway. The kinetics of the coupling of the aryl radical 2 were determined by comparison with the known rate of cyclization of 2. Similar experiments with the neopentyl bromide, 6-bromo-5,5-dimethylhex-1-ene, and its 3-oxa derivative also gave cyclized and uncyclized products, thus confirming that the SRN1 mechanism applies to the reactions. Approximate rate constants for the coupling of a neopentyl radical with the nucleophiles -SPh and -PPh2 have thus been determined.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040703
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 57
    Electronic Resource
    Electronic Resource
    Short Communications. Biphenyl-3,4′-Dinitrene (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 459-462 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photolysis of biphenyl-3,4′ -diazide in a rigid glassy matrix at 77 K yields quintet state biphenyl-3,4′ -dinitrene with zero-field splitting parameters of |D/hc- = 0.153 cm-1 and |E/hc| = 0.019 cm-1 determined by electron spin resonance spectroscopic studies. Curie plot studies are consistent with assigning the quintet to be the ground state in this species. This finding confirms qualitative connectivity-based predictions for this general connectivity type of openshell system, and is in qualitative agreement with spectral INDO-CI computational predictions for both planar and twisted geometries of the dinitrene.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040708
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 58
    Electronic Resource
    Electronic Resource
    The α-bromocyclohexanone ring: The relationship between its conformation and the ultraviolet and infrared absorption of the keto group (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 420-438 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of diterpenoids whose C-ring was an α-bromocyclohexanone showed a discontinuity in the relationship between the Br—C—C=O torsion angle and the Br…O contact distance at about 50°, below which the Br…O distance remained effectively constant at about 3.0 Å. This effect is caused by the non-compressibility of the van der Waals radii of the Br and O atoms. Analysis of the parameters for all compounds in the Cambridge Data File containing an α-bromocyclohexanone ring confirmed this phenomenon. Once the Br…O distance approaches 3.0 Å, the Br—C—C and C—C=O angles are forced open to accommodate the Br…O compression strain as the torsion angle is further reduced. An approximate value of the Br…O distance, d in Å, can be estimated for any torsion angle, ø, by the empirical equation d2 = R - S cos φ + T cos2 φ where R = 11.73, S = 3.62 and T = 0.75. There is a linear relationship between the Br…O separation and both the infrared vibration frequency v and the ultraviolet absorption wavelength δmax of the C=O group: the greater the distance, the lower is the frequency v and longer the wavelength δmax. Thus measurement of the ultraviolet and infrared spectra of a compound containing an α-bromocyclohexanone system can yield information about the Br…O distance and hence the conformation of the six-membered ring. There are also systematic trends in the effect on the spectroscopic properties of the keto group that accompany changing the halogen from fluorine through to iodine. When the halogen is axial, its electronegativity has a maximum influence on the C=O vibration frequency by a ‘through-bond’ inductive process. When the halogen is equatorial, it exerts a steric compression on the non-bonded electrons in the 2p orbital of the oxygen atom. This enhances hybridization to the sp2 state and this simultaneously strengthens the C=O bond and enlarges the n → π* energy gap. This ‘through-space’ influence is simply a process of steric compression, dependent on the size of the halogen atom. It accounts well for all of the systematic trends in both infrared and ultraviolet frequencies of the C=O group when the halogen is equatorial and eclipses the C=O bond.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040705
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 59
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040801
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 60
    Electronic Resource
    Electronic Resource
    Treatment of electrostatic effects within the molecular mechanics method. 3. Double bonds and conjugated systems (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 467-478 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The previously developed general method (IDME), which includes calculation of electrostatic and solvation effects on conformational equilibria, has been extended to molecules containing double bonds and conjugated systems. It was applied in connection with MM2 studies to the calculation of the charge distributions and dipole moments, and to the conformational energies of some β-substituted cyclohexenes, exo-methylenecyclohexanes and benzocycloheptenes. Conformational equilibria and dipole moments were well calculated. It was concluded that electrostatic interactions do not play a major role in determining conformational preferences in these compounds. On the other hand, the energies of the preferred conformations of the ten-membered ring in (E)-3β-acetoxy-5,10-seco-1(10)-cholesten-5-one are poorly calculated without the IDME procedure, and fairly well with it.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040802
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 61
    Electronic Resource
    Electronic Resource
    Theoretical models for the reduction of arylmethyl halides by triorganotin hydridesPreliminary presentation of results at combined 45th Northwest-10th Rocky Mountain Regional Meeting of the American Chemical Society, Salt Lake City, UT, 13 June 1990. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 485-491 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two mechanistic pathways have been proposed for halogen atom transfer from the benzylic positions of halomethylarenes to triorganotin radicals. These are direct atom abstraction, which might involve an extremely polar transition state, and single electron transfer followed by bond cleavage. AM1 semi-empirical calculations have been utilized to model the rate-determining step of these processes. A wide range of related families of compounds have been studied, including substituted halomethylbenzes, selected halomethyl-substituted polycyclic aromatic hydrocarbons and oxygen- and nitrogen-containing chloromethyl-substituted heteroaromatic systems. Although these calculations are relatively simple, the present results corroborate the view that chlorine and bromine atom transfer from the benzylic position to triorganotin radicals involves a direct atom abstraction in the rate-determining step whereas reduction of the corresponding iodides proceeds via an electron-transfer mechanism.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040804
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 62
    Electronic Resource
    Electronic Resource
    Ambident electrophilicity of alkyl aryl phosphates (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 516-522 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hydrolysis of dimethyl aryl phosphates, (MeO)2P(O)OAr where the ArO group is derived from N-methyl-8-hydroxyquinolinium or 4-hydroxy-(N,N,N-trimethylanilinium) ion, proceeds with the cleavage of the P—OAr and Me—O bonds. The effect of external factors on the relative contributions of those two reaction pathways was studied. The increase in temperature favours, owing to the difference in activation entropies, the reaction at carbon. The addition acetone to the aqueous reaction medium slows down the reaction at carbon more rapidly than the reaction at phosphorus, indicating higher hydration requirements of the dealkylation transition state. In water-triffuoracetic acid mixtures only the P—OAr bond cleavage is acid catalysed; the catalytic effect is superimposed on the general, decelerating medium effect. Specific nucleophilic catalysis was demonstrated for the Me—O bond fission by thiosulphate ion (ca 60-fold acceleration), and for the reaction at phosphorus by fluoride ion (ca 500-fold acceleration).
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040807
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 63
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040901
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 64
    Electronic Resource
    Electronic Resource
    Short communication. Structural studies of bromine adducts of 1,2- and 1,4-bis(phenylseleno)benzenes. Evidence for the (TB, MC) structure of 1,2-(PhSeBr2)2C6H4 (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 523-525 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1,2-Bis(phenylseleno)benzene reacted with equimolar amount of bromine to yield a trigonal bipyramidal (TB) adduct, in contrast to the molecular complex (MC) structure of selenanthrene with bromine. Whereas the structure of 1,4-(PhSeBr2)2C6H4 was (TB, TB) at the two selenium atoms, that of the 1,2-derivative was demonstrated to be (TB, MC), the first example of an MC structure of PhSeC6H4Y with Br2 [Y = 2-PhBr2Se(TB)]. Both electronic and steric effects of the group must play an important role in MC formation. Rapid structural exchange in this tetrabromide, (TB, MC) ⇄ (MC, TB), was also observed.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040808
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 65
    Electronic Resource
    Electronic Resource
    Conformations of pentan-1-OL, hexan-1-OL and their thio analogues (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 536-540 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Empirical linear relationships between standard Gibbs free energy, ΔG298°, and parachor and between standard entropy, S298°, and parachor are presented for the aliphatic series H(CH2)nX with X = CH3, CH=CH2, C≡CH, Cl, OH, SH, SCH3 and SC2H5. In the series with X = OH and SH significant deviations of points for n = 4 and 5 are observed. INDO quantum-chemical analysis points to the formation of cyclic conformers of butan-1-ol, pentan-1-ol and their corresponding thio analogues. The formation energy of the cyclic conformers (higher for thiols than for alcohols) is proportional to the sum of deviations from the linearity of the points under discussion.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040903
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 66
    Electronic Resource
    Electronic Resource
    Review commentary. Solvation, the electrophilic driving force of ionic bromination of ethylenic compounds. The addition-solvolysis analogy (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 527-535 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvation is the main driving force of electrophilic bromination since it is impossible to obtain a bromonium ion from bromine and alkene in the gas phase, whereas it is a very fast reaction in solution. The role of a protic solvent in this addition was investigated experimentally by extended Winstein-Grunwald relationships, kinetic solvent isotope effects and R, the rate ratios in two solvents of similar ionizing powers but different nucleophilicities. It is shown that electrostatic medium effects and electrophilic assistance to bromide ion departure are the main rate-determining factors of the reaction. These two contributions are roughly independent of the double bond substituents. Nucleophilic solvent assistance to positive charge development is also found; however, it provides only a small acceleration, the magnitude of which depends on alkene structure. This nucleophilic solvent involvement is annulled when crowded substituents inhibit approach of the solvent to the cationic part of the transition state or when positive charge is delocalized by conjugated electron-donating groups. These several solvent roles are identical in nature and in magnitude with those observed in heterolytic solvolysis. In halogenated solvents, the driving force of bromination arises from catalysis by a second bromine molecule which assists heterolysis of the bromine-bromine bond, leading to the bromonium-tribromide ion pair. Similar halogen catalysis occurs also in some solvolyses. Finally, return is also found in both reactions; reversible formation of bromonium ions is observed when their nucleophilic attack, the productforming last step, is made energetically difficult either by steric inhibition or by poor nucleophilicity of the trapping nucleophiles. Similarities and differences between electrophilic bromine addition and limiting solvolysis are discussed in terms of respective intermediate stabilities and heats of formation.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040902
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 67
    Electronic Resource
    Electronic Resource
    Photochemical transformations. 49.For Part 48, see Ref. 1. Solvent effects on singlet ionic and triplet photoreactions of some bridged polycyclic chlorides: Comparison with ground-state reactionsDedicated to Professor Kurt Schaffner on his 60th birthday. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 541-546 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Direct irradiations of 2-chloro-6,7 : 8,9-dibenzotricyclo [3.2.2.02,4] nona-6,8-diene (5-Cl) were conducted in cyclohexane, acetic acid and wet acetonitrile. The products are 1-methylfluoranthene (8) in all three solvents, the allylic chlorides 8-chloro-7-methylene-2,3 : 5,6-dibenzobicyclo [2.2.2] octa-2,5-diene (3-Cl) and 7-chloromethyl-2,3 : 5,6-dibenzobicyclo [2.2.2] octa-2,5,7-triene (2-Cl) in acetic acid and acetonitrile and solvolysis product amides in wet acetonitrile. Compound 5-Cl had previously been shown to be the product of triplet sensitization of 2-Cl and 3-Cl, so that the singlet reaction reverses that of the triplet. The formation of 8 from 5-Cl was quenched with piperylene, whereas that of the allylic chlorides was not. Quantum yields of products and singlet lifetimes in the three solvents were measured. The solvent effects are discussed. Deuterium-labeling results on the formation of 5-Cl from 2-Cl and of 8 from 5-Cl are reported.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040904
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 68
    Electronic Resource
    Electronic Resource
    Methyl substituent effects on the dissociation energies of Si—X bonds (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 562-565 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Empirical expressions are obtained for bond dissociation energies (BDEs) of alkylsilanes and their derivatives. It is pointed out that the sensitivity of the BDEs of Si—X bonds to methyl substitution depends on the electronegativity of the substituent X. When X is an atom or group with low or moderate electronegativity, the Si—X BDE is insensitive to methyl substitution, but when X is a halogen atom or OH, the Si—X BDEs increase with increasing methyl substitution.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040906
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 69
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of the cleavage of phthalimide in buffers of tertiary and secondary amines. Evidence of intramolecular general acid-base catalysis in the reactions of phthalimide with secondary amines (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 547-561 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction rates of the cleavage of phthalimide (PTH) were studied at 30°C in buffer solutions of trimethylamine, triethylamine, triethanolamine, carbonate, piperidine, dimethylamine, morpholine, piperazine and N-methylpiperazine at different pH values. The reactivity of carbonate, triethylamine and triethanolamine toward PTH could not be detected under the experimental conditions applied. However, triethylamine revealed nucleophilic reactivity toward non-ionized PTH (SH). The steric requirements of triethylamine and triethanolamine are ascribed to the absence of nucleophilic reactivities of these amines toward SH. Secondary amines show nucleophilic reactivity toward both SH and ionized PTH (S-). The absence of nucleophilic reactivity of trimethylamine and the presence of nucleophilic reactivity of secondary amines toward S- are attributed to the occurrence of intramolecular general acid-base catalysis due to the presence of a mobile proton at the nucleophilic site of the nucleophile. Intermolecular general base catalysis was observed in the reactions of SH with all secondary amines except piperidine and such catalysis could be detected in the reactions of S- with morpholine, piperazine and N-methylpiperazine. Nucleophilic second-order rate constants for the reactions of secondary amines with SH (k1) and S- (k2) reveal the Brønsted plots of slopes of ca 0.8 and 0.3, respectively. Similarly, the general base-catalysed third-order rate constants (k4) for the reactions of secondary amines with SH yield a Brønsted plot of slope 1.2. These observations suggest the occurrence of diffusion-controlled trapping stepwise and pre-association stepwise mechanisms in the aminolysis of non-ionized and ionized phthalimide, respectively.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040905
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 70
    Electronic Resource
    Electronic Resource
    Multiplicities of π-ylide ground states: Computational evidence for a breakdown of aromaticity arguments (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 566-572 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: AM1 and 3-21G computations, on the lowest singlet state of selected π-ylides, support the earlier conclusion that π-ylides are highly polar with highly reactive side-chains. The computations also indicate that the corresponding triplet states are lower in energy and have substantially reduced polarity. Contrary to the expectations derived from Hückel calculations, AM1 and 3-21G calculations suggest that the best π-ylide structures have non-aromatic rings. The heats of isomerization contradict earlier conclusions reached using topological resonance energies. π-Ylides are expected to afford different product structures depending on the electronic state of the π-ylide involved in a given cycloaddition reaction.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040907
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 71
    Electronic Resource
    Electronic Resource
    Protein immobilization by aminolysis of cellulose xanthate esters (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 573-578 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: P-Nitrobenzyl cellulose xanthate (CelXNB) was obtained with a degree of substitution (DS) in the range 0.5-3. The first order rate constant for hydrolysis of CelXNB at 25°C, extrapolated to zero buffer concentration, is hydroxide ion catalysed, whereas the water-catalyed path is about 2000 times faster than that observed for p-nitrobenzyl ethylxanthate (EXNB), probably owing to the highly ordered cybotactic region of cellulose. Aminolysis of CelXNB produces the corresponding thioncarbamate ester; for simple alkylamines, the second-order rate constants are similar to those obtained for EXNB. The secod-order rate constants are similar to those obtained for EXNB. The second-order rate constants at pH 11 for immobilization of bacterial α-amylase and bovine serum albumin were 13.4 and 112 1 mol-1 s-1, respectively, unexpectedly high values when compared with simple alkylamines, even considering the concentration of external reactive groups of the proteins. CelXNB with low DS should release 1 mol of p-nitro-α-toluenethiol for every mole of protein that becomes immobilized. The net weight increase of the cellulose matrix allows the calculation of the absolute molecular weight of the protein. Preliminary results support this assumption.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040908
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 72
    Electronic Resource
    Electronic Resource
    Gas-phase thermolysis of aryl tert-butyl disulphides (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 579-585 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The pyrolysis kinetics of RC6H4SS—t—C4H9 (R=H, p-NO2, p-Cl, p-F) were determined at 390-450°C and 7-15 Torr in a stirred-flow reactor using toluene as carrier gas. The reaction products were 95% isobutene, 5% isobutane and the corresponding RC6H4SSH disulphanes. The first-order rate constants, k (s-1), based on isobutene production, followed the Arrhenius equations: phenyl tert-butyl disulphide, k = 1013.49±0.31 exp (- 182 ± 4 kJ mol-1)(RT)-1; pnitrophenyl tert-butyl disulphide, k = 1013.46 ± 0.32 [exp(- 185 ± 5 kJ mol-1)(RT)-1]; p-chlorophenyl tert-butyl disulphide, k = 1014.44 ± 0.66 [exp(- 196 ± 9 kJ mol-1)(RT)-1; p-fluorophenyl tert-butyl disulphide, k = 1010.80 ± 0.16 exp(- 144.5 ± 2 kJ mol -1)(RT)-1]; The observed reactivities, within the above temperature range, follow the order p—F 〉 H 〉 p—Cl 〉 p—NO2. A four-centre, cuadrupolar cyclic transition state mechanism is proposed for the formation of the isobutene and aryldisulphane products. The optimized ground-state molecular geometries of the reactants were calculated by using the MINDO/3 procedure.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040909
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 73
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041001
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 74
    Electronic Resource
    Electronic Resource
    Vinyl ether hydrolysis. 25. Effect of α- and β-trimethylsilyl substitution (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 587-591 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rates of hydrolysis catalyzed by dilute perchloric acid were measured for the vinyl ethers MeOC(SiMe3)=CH2, EtOC(SiMe3)=CH2, cis-EtOCH=CHSiMe3, MeOC(t-Bu)=CH2 and EtOC(t-Bu)=CH2 in wholly aqueous solution and for MeOCH=CH2, MeOC(SiMe3)=CH2 and MeOC(t-Bu)=CH2 in ethanol - water (4:1), in order to assess the effects of silyl substitution on the stability of the carbocations formed in the rate-determining step of these reactions. The results for α-substitution give the reactivity order H 〈 SiMe3 〈 t-Bu, with a greater spread (103) in wholly aqueous solution than in the mixed solvent (102). The β-trimethylsilyl substituent shows a modest 100-fold acceleration over hydrogen; the diminished magnitude of this effect relative to the 1012-fold acceleration found recently in a cyclohexyl solvolysis reaction is attributed to the imposition of a conformation in the transition state of vinyl ether hydrolysis that is far from optimum for hyperconjugative electron donation.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041002
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 75
    Electronic Resource
    Electronic Resource
    An ene reaction with a polar transition state as ascertained from solvent effects (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 605-610 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A kinetic study is reported for the ene reaction between methyl acrylate as the enophile and β-pinene, with aluminium chloride as catalyst, in a series of solvents varying in polarity. These experiments point to a transition state having pronounced zwitterionic character, in line with earlier suggestions in the literature. An unexpected and significant change of the rate constant with the initial concentrations is also found.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041004
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 76
    Electronic Resource
    Electronic Resource
    Solvatochromism of dyes. Part I. Solvatochromism of merocyanines. Derivatives of the 7H-indolo [1,2-a] quinolinium system. A new model of solvatochromism (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 592-604 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new approximate model of the solvatochromism of merocyanines is presented. In solution merocyanines exist in the electronic ground state as a mixture of three different structures. Since only one longest wavelength band is observed in the UV - visible absorption spectra of such merocyanines, their lowest excited states are roughly assumed to be represented by a single structure. The molar fraction of each of the three structures of merocyanines in the ground state is a function of the solvent polarity. This (VBHB) model has been verified using merocyanines prepared from 5-(hydroxyaryl)-7,7-dimethyl-7H-indolo [1,2-a] quinolinium perchlorates. The analysis of the experimental data suggests that the three ground-state structures of merocyanines are the vinylogous amide (V) and the betaine as the free (B) or hydrogen-bonded (HB) form.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041003
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 77
    Electronic Resource
    Electronic Resource
    Steric effects of alkyl groups: A ‘cone angle’ approach (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 611-617 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A ‘cone angle’, θR, is defined for an alkyl group (R), which is proposed as a measure of the steric effect exerted by the group. The θR values for some 57 groups have been calculated mathematically by constructing the corresponding Corey - Pauling - Koltun molecular models. The variation in θR with the bulk of a group is satisfactory. However not all types of alkyl groups can be accommodated in this cone angle approach. In the case of the groups for which the cone angle can be measured, correspondences between θR and the two existing steric parameters (Taft's Es scale and Dubois' E′s scale) have been established. For some 23 alkyl groups θR has been used to explain the variation in the rate constant of the base-catalysed hydrolysis of RCOOEt with the nature of R. Our studies independently substantiate the basic assumptions of the Taft - Ingold hypothesis that, while the base-catalysed ester hydrolysis is mostly controlled by the steric and electronic effects of the R group, the acid-catalysed one is controlled almost solely be the steric effect.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041005
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 78
    Electronic Resource
    Electronic Resource
    Gas-phase acidity of some α-keto aldoximes: Experiment and theory (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 285-292 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Experimental gas-phase acidities of 2-oxopropanaloximes, XCH2COCH=NOH (X = H, CH3S, CH3SO, CH3SO2; compounds 1-4), were determined by Fourier transform ion cyclotron resonance (FT-ICR) spectrometry. The values are δ Gacid° = 1401, 1381, 1360 and 1351 kJ mol-1 for 1, 2, 3, and 4, respectively. Molecular orbital calculations using the semi-empirical AM1 method provided information on the geometry and relative energy of neutrals species 1-4 and their conjugate bases, together with charge distributions and entropies of deprotonation. It is demonstrated that the proton abstraction occurs preferentially at the oxime function; the formation of an enolate as a conjugate base is unfavourable by 70-140 kJ mol-1. The large variation of the gas-phase acidities for 1-4 is explained in terms of the field/inductive empirical substituent constant σF. The variation of solution acidities appears to be comparatively strongly attenuated. This attenuation is attributed mainly to charge delocalization in the anion, which was confirmed by charge density calculations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040505
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 79
    Electronic Resource
    Electronic Resource
    Depurination of (dien)Pt(II) complexes of purine deoxyribonucleosides. Comparison with the effects of (dien)Pd(II) ion complexing (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 301-309 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: First-order rate constants for the hydrolytic depurination of 2′-deoxyinosine and its various (dien)Pt(II) ion complexes were measured over the acidic pH range. The rate profiles obtained indicate that the uncomplexed nucleoside and its N1-(dien)Pt(II) complex are depurinated via mono- and di-protonated species, whereas the N7-(dien)Pt(II) and N1, N7-di(dien)Pt(II) complexes exhibit significant spontaneous hydrolysis, which competes with a markedly retarded acid-catalysed reaction. Rate constants for the various partial reactions were calculated and the results were employed to explain the effects that (dien)Pd(II) ion exerted on depurination rates of the same compounds. Similar measurements were carried out with the N1, N7-di(dien)Pt(II) complex of 2′-deoxyadenosine in order to further the understanding of the previously reported rate-enhancing effect of (dien)Pd(II) ion on the depurination of 2′-deoxyadenosine.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040507
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 80
    Electronic Resource
    Electronic Resource
    Crystallographic studies of intra- and inter- molecular interactions. Part VI. Crystal and molecular structure of N,N′-dimethyl-N′-phenylsulphonylformamidine. Equalization of CN bond lengths in the amidine fragment as a result of substituent effects due to push-pull (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 331-335 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal and molecular structure of N,N-dimethyl-N′-phenylsulphonylformamidine is solved by direct methods and refined to R = 0.041 for 935 reflections, Equalization of CN bond lengths in the amidine fragment is discussed in terms of a push - pull effect operating between the N,N-dimethyl and SO2Ph groups. A significant role of the substituent at the functional carbon on the degree of π-electron delocalization on the NCN fragment is interpreted by use of the HOSE model.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040602
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 81
    Electronic Resource
    Electronic Resource
    Reactivity and reaction patterns of alkyl alkoxybenzene radical cations. Mechanistic pathways of the reactions between 2,5-DI-tert-Butyl-1, 4-Dimethoxybenzene and perfluorodiacyl peroxides (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 1-6 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In the reactions of 2,5-di-tert-butyl-1,4-dimethoxybezene (1) with different oxidants, the radical cation 1+. is always detectable by EPR. However, the observed reactivity of 1+. depends greatly on the oxidation systems employed. In S2O82-—Cu2+—HOAc and Ce4+—HOAc systems (HOAc = acetic acid), 1+. appears to have long lifetimes and does not undergo fragmentation spontaneously. In contrast, in (RFCO2)2—CF2CICFCI2 (F113) systems, the readily formed 1+. is short-lived, and large amounts of de-tert-butylation products have been isolated. Experimental results imply that the C—C bond cleavage involved in de-tert-butylation could be a consequence of an attack by perfluoroacyloxy radical on 1+. in their original solvent cage. The fact that addition of methanol to the reaction mixture leads to the formation of a large amount of tBuOCH3 (46%) and other evidence suggest that the tert-butyl group leaves as a carbocation. On the basis of these results, we conclude that the reactions of 1 with (RFCO2)2 are initiated by electron transfer and followed by a fast coupling of various radical species, namely, 1+. with RFCO2 or with RF in the solvent cage, to form σ-complexes which collapse or react with nucleophiles to yield the final products.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040102
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 82
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040701
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 83
    Electronic Resource
    Electronic Resource
    Applicability of excess acidity functions in low-acidity media (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 413-419 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It is demonstrated that excess acidity functions do not correspond well to the pH scale in dilute solutions. Acidity constants, pKBH+, of seven moderately weak bases were determined; they were calculated by means of excess acidity functions, since the corresponding ionizations occur at acidity levels where the pH scale is partly used. The excess acidity method permitted extrapolation of measurements made in concentrated acids down to dilute solutions only up to about 5% (w/w) perchloric acid.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040704
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 84
    Electronic Resource
    Electronic Resource
    Correlation of alkyl and polar substituents in the elimination kinetics of 2-substituted ethyl methanesulphonates in the gas phase (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 399-403 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the elimination of several polar 2-substituted ethyl methanesulphonates in the gas phase were determined in a static system, seasoned with allylbromide, and in the presence of at least equal amount of the freeradical suppressor propene and/toluene. The working temperature and pressure ranges were 290-360°C and 31°199 Torr (1 Torr = 133.3 Pa), respectively. The reactions are homogeneous, unimolecular, show a first-order rate law and take place according to the following equations: for 3-chloropropyl methanesulphonate, log k1 (s-1) = (12.01 ± 0.18) - (171.7 ± 2.1) kJ mol-1 (2.303RT)-1; for 4-chlorobutyl methanesulphonate, log k1 (S-1) = (11.78 ± 0.31) - (166.1 ± 3.5) kJ mol-1 (2.303RT)-1; for 3-methoxypropyl methanesulphonate, log k1 (s-1) = (11.50 ± 0.36) - (163.3 ± 4.0) kJ Mol-1 (2.303RT)-1; and for 2-ethoxyethyl methanesulphonate, log k1 (s-1) = (11.52 ± 0.37) - (167.3 ± 4.1) kJ mol-1 (2.303RT)-1. The present data together with those reported in the literature show that alkyl 2-substituted ethyl methanesulphonates give an approximate straight line when log k/ko vs σ* values (ρ* = -0.82 ± 0.088, intercept = 0.0084 ± 0.0209 and correlation coefficient r = 0.967 at 320°C) are plotted. However, polar substituents at the 2-position of ethyl methanesulphonates give rise to an inflection point at σ*(CH3) = 0.00 into another very good straight line (σ* = -0.29 ± 0.013, intercept = -0.0065 ± 0.0213 and r = 0.994 at 320°C). The mechanism of these reactions is considered to be heterolytic in nature, proceeding in terms of an intimate ion-pair intermediate.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040702
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 85
    Electronic Resource
    Electronic Resource
    Correlations between empirical lewis acid-base solvent parameters and the thermodynamic parameters of ion solvation. Part II. Acidity parameters of cations and basicity parameters of anions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 439-448 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The parameters α, β and γ of the equation WΔsGf(MX) = αBKT + βET + γ were calculated and analysed for different salts (MX) in pure solvents and in non-aqueous solvent-water mixtures (S). Among 109 different equations, only 64 were taken for the final analysis since in the case of 38 equations the parameters BKT and ET were highly correlated. After a statistical analysis and normalization, on the basis of the coefficients α and β obtained, it was found that the ions analysed may be divided into three classes characterized by the different dependences of α on β: class I, H+, Li+, Na+, Rb +, Cs+, Me4N+, Cl-, Br- and I-, where αN = 1.074βN + 1.639; class II, Ag+, Cl-, Br-, I-, OAc-, SCN- and N3- where αN = 2.057βN + 2.147; and class III, Ph4As+, BPh4-, Ph4C and Ph4Ge, where αN is variable and βN is almost constant. Two main conclusions can be drawn out from the results obtained: the behaviour of ions considered as Lewis acids and bases reflects different hard-soft properties of the ions, and the behaviour of the Ph4As+ ion is different from that of BPh4-.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040706
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 86
    Electronic Resource
    Electronic Resource
    AM1 studies on the intramolecular cyclization of ω-haloenolate anionsDetermination of reactivity by MO Theory, Part 72. For Part 71, see Ref. 1. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 449-458 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intramolecular cyclizations of ω-haloenolate anions, -CαH2—C(=O)—(CH2)n-3—CωH2—X with X = F, Cl and Br and n = 3-7, were investigated by the AM1 method. In most cases, cycloketone formation proceeds more favourably than cycloether formation, as predicted by the HSAB principle. The reactivity increases in the order X = F 〈 Br 〈 Cl for both processes, and for cycloether formation it is in the order n = 3 〈 4 〈 7 〈 6 〈 5 for all X but the relative order for n = 5 and 6 reverses in favour of n = 6 for cycloketone formation with X = Cl and Br. The softness of the acid centre, Cω, decreases for a harder X( = F) whereas it increases for a softer X( = Br). Thus the reactivity order with respect to X suggests that the softness of the base centres O and Cα belongs to the borderline class. The transition state (TS) structures indicate that the BEP principle is obeyed in all cases, and a less reactive process has a more product-like TS.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 87
    Electronic Resource
    Electronic Resource
    Short communication. Solvolysis of some benzylic and non-benzylic tertiary p-nitrobenzoates. A new YBnOPNB scale (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 463-466 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new Y scale for the correlation of solvolytic reactivities for benzylic ρ-nitrobenzoates was established based on rate data for 2-phenyl-2-adamantyl ρ-nitrobenzoate, and from which the solvent assistance in the solvolysis of tert-cumyl ρ-nitrobenzoate is suggested.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040709
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 88
    Electronic Resource
    Electronic Resource
    Experimental and theoretical studies of the effects of hydration on proton exchange equilibria (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 479-484 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Theoretical calculations with the ab initio molecular orbital STO-3G basis set on the effect of trihydration on the relative acidities of 3- and 4-substituted phenols, 4-substituted quinuclidinium ions and 4-substituted bicyclo [2.2.2]octylammonium ions are reported. These results are contrasted with calculations on non-hydrated species and compared with results in aqueous solution and in the gas phase. Unlike results for smaller molecules such as substituted acetic acids and methylammonium ions, the solvation effects of three molecules of water are far short of that observed in going from the gas phase to aqueous solution. Reasons for this are discussed in the context of solvent attenuation factors for various molecules.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040803
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 89
    Electronic Resource
    Electronic Resource
    Preparation, characterization and rearrangement pathways of 10-alkyl-9-decalyl carbocations (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 492-500 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The preparation and characterization of 10-methyl- and 10-ethyl-9-decalyl cations is described. Both cations undergo a rapid, degenerate 10, 9-alkyl shift, but the ethyl group migration is about 700 times slower at -120°C than that of the methyl group. This preference is opposite to that usually found for alkyl migration rates and, on the basis of MO calculations, it is suggested that a conformational interchange may be the rate-determining step. Both cations irreversibly rearrange at about -100°C, giving in the methyl case the rearrangement cascade 10-methyl-9-decalyl → cis-1-methyldecalyl → trans-1-methyldecalyl → trans-2-methyldecalyl. Each of these rearrangement ions was independently prepared and characterized by NMR spectroscopy. One can rationalize the initial formation of the less stable cis ring junction on the basis of suprafacial hydride and methyl shifts. Attempts to add molecular hydrogen to the 10-methyl-9-decalyl cation were unsuccessful.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040805
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 90
    Electronic Resource
    Electronic Resource
    Product-determining factors in the grignard reactions of benzophenones. The role of the structure of alkyl groups in grignard reagents (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 501-515 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The mechanism of the Grignard reactions of substituted benzophenones with two kinds of alkyl Grignard reagent, n-C3H7MgBr, and i-C3H7MgBr, was investigated. In these reactions, both addition and reduction products were also generated. Based on the results of product analysis and stopped-flow, ESR and association measurements, it was confirmed that the product distribution was governed by several factors: the oxidizing ability of benzophenones, the association ability of Grignard reagents and the structure of alkyl groups of Grignard reagents. In particular, the strength of C—Mg and β-C—H bonds of Grignard reagents could strongly affect the product distribution.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040806
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 91
    Electronic Resource
    Electronic Resource
    The effect of pressure on swern-moffatt oxidations (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 639-642 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rates of oxidation of cyclohexanol by dimethyl sulphoxide in conjunction both with acetic anhydride and with dicyclohexylcarbodiimide have been measured with variation of both temperature and pressure. Activation volumes were found to be -25 and -34 cm3 mol-1, respectively, and the absence of an α—d PKIE was noted. The reaction mechanism is discussed in the context of these values.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041009
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 92
    Electronic Resource
    Electronic Resource
    Estimation of thermodynamic stability and charge distribution for unknown molecules: Nitro derivatives of cubane (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 714-720 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Three useful procedures for estimating the thermodynamic stability and charge distribution of moderately complex unknown species are illustrated by the successive nitration of cubane. (1) Five different, but interrelated, energy criteria are employed, which leads to mutually supportive conclusions that overcome deficiencies in any one of the single measures. (2) Mulliken charge and overlap populations can lead to correct bond strength trends if appropriate averaging over bond types is carried out. (3) Lewis - Langmuir atomic charges, an interpolation between the formal charges of Lewis dot structures and oxidation numbers which does not require use of computers, provides atomic charges similar to those from ab initio, wavefunctions. The simplicity of this scheme aids in identifying the chemical and topological origin of molecular charge distributions. Ab initio, calculations for the strain energies and heats of reaction for four different reaction sequences are reported, together with Mulliken atomic charges and overlap populations for the nitrocubanes. Trends in these measures suggest that hexa- and octa-nitrocubane are thermodynamically stable species.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041203
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 93
    Electronic Resource
    Electronic Resource
    Effect of hexadecyltrimethylammonium bromide micelles on the hydrolysis of substituted benzoate esters (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 13-18 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The alkaline hydrolysis of nine para-substituted phenyl esters of para-substituted benzoates was studied in the presence and absence of hexadecyltrimethylammonium bromide (CTAB) micelles. The second-order rate constant for alkaline hydrolysis in CTAB micelles (K2m) was calculated using a pseudo-phase ion-exchange model. the substituent effect on the second-order rate constant in the aqueous phase (k2w) and on k2m was analysed using Hammett's σ ρ plots. The calculated ρ values in micelles were 0.8 unit. larger than those in water. The effective low dielectric constant in the micellar surface may be responsible for the general effect of increasing the sensitivity of reactions to the electronic effect of substituents in micelles.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040104
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 94
    Electronic Resource
    Electronic Resource
    1,5-Sigmatropic shifts of bromine over a cyclopentadiene ring (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 31-47 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intrinsic mechanism of circumambulatory rearrangements of 5-bromo-5-methyl-1,2,3,4-tetramethoxycarbonylcyclopentadiene, 5-bromo-1,2,3,4 5-pentamethoxycarbonylcyclopentadien and 5-bromo- 1,2,3,4,5-pentaphenylcyclopentadiene due to sigmatropic shifts of bromine over the cyclopentadiene ring was proved, using the dynamic 13C and 1H NMR technique, to be governed by successive intramolecular 1,5-sigmatropic shifts. Semi-empirical AM1 and MINDO/3 calculations of reactions paths performed for fluoro-, chloro- and bromocyclopentadienes are in accord with the conclusion of a preference for a 1,5- over a 1,3-shift reaction path of halogen migration over a cyclopentadiene system. Intramolecular 1,5-sigmatropic shifts of chlorine in 5-chloro-5-methyl-1,2,3,4-tetramethoxycarbonylcyclopentadiene with the free energy barrier of ΔG298+ = 26.1 kcal mol-1 were studied using 1H NMR spectroscopy.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040107
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 95
    Electronic Resource
    Electronic Resource
    Taft's substituent constants, σ* and σI, and Huheey's group electronegativity (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 96-100 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: For 34 groups, Taft's substituent constants σ* and σI are found to correlate well (r = 0.962 and 0.948) with Huheey's group electronegativity (χH) when Taft's steric parameter Es for a group is mixed with σ* and σI: From these equations, it follows that for a particular chemical group G, σ*(G) ≍ 8σI(G). Since the σ* scale is essentially based on the σI scale, the small inherent steric component in σI is amplified in the case of the σ* by a factor of ca 8. An analysis shows that χH represents the electronegativity of a group when the group is considered to be a mere collection of non-bonded, charged and suitably hybridized atoms. Thus σ* and σI are found to represent the electronegativity of a group in the spirit of the χH. It is concluded that a chemical group can be viewed as a collection of non-interacting atoms. Although there is evidence that a molecule can sometimes be treated similarly, for a group such a situation is novel.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040205
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 96
    Electronic Resource
    Electronic Resource
    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040301
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 97
    Electronic Resource
    Electronic Resource
    Theoretical study of simple push-pull ethylenes in solution (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 141-148 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The influence of solvation on the Z - E isomerization process of three representative molecules of simple push-pull ethylenes [H2N(H)C1=C2(H)R = NO2, COH and CN] derived from aminoethylene was investigated by means of RHF-SCF ab initio calculations at the 3-21 + G level. Solute-solvent interactions were modelled by a cavity model. The shape of the cavity is based on electronic isodensity surfaces. By using an ellipsoidal cavity very close to the isodensity surface, the perturbation due to the solvent takes an analytical form which is incorporated into the Hartree-Fock equations and leads to efficient quantum chemical computations. The polarization of the solutes under the influence of the solvent is noticeable and was analysed in detail. Similarly, the barriers to internal rotations are substantially modified by the solvent: the barrier around the C=C double bond is appreciably decreased in the thermal mechanism whereas its lowering is less important in the anionic mechanism; in contrast, the barrier around the C-1—N bond is slightly increased. The variation of the barriers with the nature of the acceptor group is fairly well reproduced by the computations. The electronic structure of the push-pull ethylene molecules and the modifications of this structure under the influence of the solvent are analysed in detail.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040304
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 98
    Electronic Resource
    Electronic Resource
    Aromaticity as a multi-dimensional phenomenon (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 163-169 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The classification of aromaticity criteria is studied. New aromaticity criteria are developed and discussed. A statistical analysis of such criteria is presented and compared with a similar analysis of the recent literature. It is shown that aromaticity is at least a two-dimensional phenomenon. The classification of the compounds depends on the type of criteria included in the analysis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040307
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 99
    Electronic Resource
    Electronic Resource
    AB initio MO study of the halogen cation basicities of some organic bases (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 177-191 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hartree - Fock calculations were performed to investigate the structure and relative stabilities of complexes between halogen cations and first- and second-row bases. It is shown by means of both a qualitative perturbation molecular orbital treatment and a topological analysis of the electronic charge density that second-row bases present enhanced halogen cation basicities compared with first-row bases. In this respect the results predict that although the fluorine cation basicity of water is smaller than its proton affinity, the fluorine cation basicities of SH2, thioether, phosphine and trimethylphosphine are considerably higher than their proton basicities. Similarly, phosphine and trimethylphosphine should have chlorine cation basicities greater than their proton affinities, in contrast with ammonia and trimethylamine. The results also show that fluorine and chlorine cation basicities are more sensitive to methyl substitution than proton affinities.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040309
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 100
    Electronic Resource
    Electronic Resource
    Micellar effects on the alkaline hydrolysis of N-alkyl-4-cyanopyridinium ions. An example of micelle-induced regiochemical selectivity (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 207-216 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rates of the reaction of N-alkyl-4-cyanopyridinium (RCP) ions [alkyl = CH3 (MCP), n-C4H9 (BCP), n-C8H17 (OCP), n-C12H25 (DCP)] with OH- ion in water are independent of chain length and RCP concentration up to 0.001 M. The ratios of the concentrations of the reaction products, N-alkyl-4-pyridone (P) and N-alkyl-4-carboxamidopyridinium (A), P/A, are similar for all substrates. In water the P/A ratios increase with pH, reaching a plateau value of ca 2 at pH ≥ 13. Added salts slightly decrease the reaction rate and do not affect the P/A ratios. In aqueous solutions, addition of dioxane increases both rates and P/A ratios. Micelles of hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide; CTAB) and 3-(N,N-dimethyl dodecyl ammonium)propane-1-sulphonate (SDP) catalyse the alkaline hydrolysis of OCP and DCP and increase the yield of pyridone with BCP, OCP and DCP. In micellar CTAB and SDP the attack of OH- on RCP occurs almost exclusively at the 4-position of the pyridinium ring. Sodium dodecyl sulphate micelles inhibit the reaction and produce small changes in the P/A ratio. The regiochemical selectivity produced by micelles, leading to a preference for the attack of OH- at the pyridinium ring, was rationalized in terms of the low effective dielectric constant at the micelle-water interface.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040403
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...