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  • 1990-1994  (790)
  • 1890-1899
  • 1990  (790)
  • 1897
  • Engineering  (558)
  • Physical Chemistry  (232)
  • 1
    Electronic Resource
    Electronic Resource
    A computer program for waveguide analysis using high-order, vector, finite elements (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 33-38 
    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 computer program has been written for the analysis and design of arbitrarily shaped waveguides, containing dielectric and magnetic materials. The program calculates the propagating modes of the waveguide by the three-component vector finite element method. High accuracy is achieved by the use of high-order elements, and by the inclusion of singular trial functions near sharp metal edges. An efficient algorithm based on the conjugate gradient method is used to solve the algebraic eigenvalue problem. Results are given for rib waveguide and fin-line.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030105
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  • 2
    Electronic Resource
    Electronic Resource
    Modelling of the generation of Ga interstitials during the diffusion of Zn into GaAs (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 91-97 
    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 diffusion of Zn into a GaAs crystal is modelled using numerical techniques similar to those of Zahari and Tuck.1 This technique does not directly solve any differential equations, the physical processes are directly modelled. The diffusion of Zn is assumed to be by the kick-out mechanism. In this mechanism the Zn atoms diffuse into the crystal interstitially with a constant diffusion coefficient. The interstitial Zn atoms transfer to the substitutional lattice site by kicking out a Ga atom. The incorporation of the Zn atoms on to the lattice sites is assumed to take place at a rate much greater than the diffusion of the interstitial Zn. The diffusion of the generated Ga interstitial is also contained in the model. The effect on the Zn concentration profile and Ga interstitial concentration of varying both the Ga interstitial diffusivity and equilibrium concentration has been examined. Finally, the implications of these results on Zn induced disordering of GaAs/AlAs superlattices is discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030205
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  • 3
    Electronic Resource
    Electronic Resource
    The modelling of networks with frequently changing topology whilst maintaining a constant system matrix (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 11-21 
    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 describes a novel technique with which a system with changing topology can be modelled whilst maintaining a constant system matrix. This technique employs a new transmission-line switch model which has a constant characteristic impedance, irrespective of its state. The method is explained, compared with the switched-resistance method and demonstrated by two examples. It has been found that the proposed method offers substantial advantages in the formulation of the problems and in the efficiency of computation.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030103
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  • 4
    Electronic Resource
    Electronic Resource
    Functional relaxations and spectral techniques in Computer-Aided circuit analysis (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 183-193 
    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: Analysis of transients in integrated circuits is performed with the use of highly specialized computer programs. The transient responses are computed using time-marching integration methods and require a substantial amount of computer time. A new method based on spectral analysis and waveform relaxation is proposed. The method results in a substantial saving in computing time without compromising the accuracy. A basic algorithm utilizing the spectral technique in a relaxation framework is described. A prototype simulator based on the algorithm was developed and used to simulate certain types of CMOS circuits. The results showed a significant time savings in comparison with the widely used circuit simulator ‘SPICE’. Example circuits and relevant results are provided.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030303
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  • 5
    Electronic Resource
    Electronic Resource
    Substructuring of space and time in TLM diffusion applications (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 207-214 
    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 simple method is described for spatial substructuring of meshes used in TLM diffusion routines in such a way as to enable discontinuous mesh lines to be used. A method of operating TLM diffusion routines using different timesteps in different spatial regions is also described. For both aspects, results are compared with those derived using standard TLM techniques.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030305
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  • 6
    Electronic Resource
    Electronic Resource
    Modelling of electrically thick cylindrical antennas (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 195-206 
    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: Hallen's integral equation has been used as the basis for the formulation of cylindrical antenna theories for many years. Being a Fredholm integral equation of the first kind, its solution is mathematically an ill-posed problem. The stability of the numerical methods based on this integral equation is dependent on the singularity and the non-smoothness of the kernel function. For electrically thick cylindrical antennas, the dominance of the singular part of the kernel (logarithmic) is weakened and the kernel function becomes relatively smooth. This observation implies possible deteriorations of the stability of the numerical methods based on Hallen's integral equation. This paper describes the development of an alternative formulation for the electrically thick cylindrical antennas based on the singular integral equation of the first kind with a Cauchy-type kernel which eliminates the potential instability problem. A numerical method based on this formulation of the antenna problem has been implemented and case studies show that it is very stable and efficient for the numerical modelling of electrically thick cylindrical antennas.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030304
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  • 7
    Electronic Resource
    Electronic Resource
    Numerical solution of inhomogeneous and non-linear ordinary differential equations using the TLM multicompartment model (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 215-228 
    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 paper presents a simple algorithm for solving a system of inhomogeneous high order differential equations with variable coefficients. The method also provides a numerical solution to non-linear ordinary differential equations. The technique is based on reducing the high order equations into a system of first order rate equations. Through a simple translation process, the variables in the reduced set of equations are solved simultaneously by an iterative scheme using the TLM multicompartment model. The numerical technique is demonstrated by solving well-known second order differential equations. The numerical solutions are compared with the analytical solutions to the differential equations.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030306
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  • 8
    Electronic Resource
    Electronic Resource
    Call for Papers (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), 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.1660030307
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  • 9
    Electronic Resource
    Electronic Resource
    Masthead (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990) 
    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.1660030401
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  • 10
    Electronic Resource
    Electronic Resource
    Editorial (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), 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.1660030402
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  • 11
    Electronic Resource
    Electronic Resource
    Full-wave analysis of multiport microstrip discontinuities using a superposition principle and mode-matching technique (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 259-268 
    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: Accurate full-wave analysis of shielded microstrip discontinuities, based on a mode-matching technique and employing Kühn's method is presented. Finite thickness of the strip metallization is taken into account. Examples include bends, T-junctions, and crossings.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030406
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  • 12
    Electronic Resource
    Electronic Resource
    Characterization of microstrip antennas using the TLM simulation associated with a Prony-Pisarenko method (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 269-285 
    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 matrix (TLM) method enables simulation of interior electromagnetic field propagation problems. With the use of absorbent walls, we can simulate exterior problems such as the radiaition of a microstrip antenna. The input impedance is deduced from the standing wave observed in the feedline. The radiation pattern is determined from the field over a plane located in the immediate vicinity of the antenna, using the theory of radiating apertures. However, the CPU time and memory space involved are excessive. Since the radiating structure has several resonant frequencies, it is convenient to apply classical digital signal processing techniques such as finite impulse response filtering associated with a linear prediction method. The present paper focuses on a Prony-Pisarenko method to improve on the TLM method in terms of both computation time and precision of the frequency-domain analysis of the results. In this case, overall CPU time is reduced by a factor of 2 to 3. The paper discusses the results obtained for radiation patterns. This represents a new field of application for the TLM method whose drawbacks are reduced by using appropriate signal processing methods.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030407
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  • 13
    Electronic Resource
    Electronic Resource
    Call for Papers (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 75-75 
    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.1660030109
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  • 14
    Electronic Resource
    Electronic Resource
    Editorial (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 77-77 
    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.1660030202
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  • 15
    Electronic Resource
    Electronic Resource
    Call for Paper (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 78-78 
    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.1660030203
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  • 16
    Electronic Resource
    Electronic Resource
    Automatic timestepping in TLM routines for the modelling of thermal diffusion processes (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 127-136 
    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: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030208
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  • 17
    Electronic Resource
    Electronic Resource
    Multiple multipole (MMP) computations of guided waves and waveguide discontinuities (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 247-257 
    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 MMP (multiple multipole) code, that is based on the generalized multipole technique (GMT), offers several features to overcome problems occurring in computations of guided waves and waveguide discontinuities. The most important problems and the corresponding MMP solutions are outlined. The procedure is illustrated with different examples which demonstrate the wide range of applications of the code.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030405
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  • 18
    Electronic Resource
    Electronic Resource
    A new time-domain transverse resonance method in solving guided wave problems (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 229-234 
    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 time-domain approach based on the frequency-domain transverse resonance method is proposed to solve guided wave problems. This new method is capable of solving both the two-dimensional and the three-dimensional propagation problems. The structure under investigation is cut into individual substructures. Time-domain Green's functions of each substructure are computed via the analytical inverse Laplace transform of the frequency-domain Green's functions. The original problem is reconstructed by connecting the cut-out substructures together through the interface boundary conditions. In order to verify the present approach, the empty rectangular waveguide is used as a comparison. With accurately calculated time-domain Green's functions, the data obtained are in good agreement with the analytical results.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030403
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  • 19
    Electronic Resource
    Electronic Resource
    Analysis of passive microwave devices by using three-dimensional tangential vector finite elements (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 235-246 
    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: There are two major difficulties in applying the finite element method to the analysis of microwave devices in three dimensions. One is to obtain a stable vector finite element which does not generate spurious modes, or non-physical solutions, in the numerical analysis. The other is to model efficiently the coupling of port regions and the discontinuity region. In this paper, we describe the application of two new finite element techniques, the tangential vector finite element method and the transfinite element method, for modelling three-dimensional microwave devices. The tangential vector finite element method, unlike the conventional nodal finite element methods, imposes only the tangential continuity of the vector unknown across elements' boundaries. As a result, there would be no spurious modes, and reliable solutions are obtained. The transfinite element method, which combines the modal basis functions and the finite element basis functions through the variational technique, provides an efficient way to model the open boundary nature of the device. To validate the current analysis, a low VSWR waveguide connector and two microstrip low-pass filters are analysed. Numerical results agree very well with the measurements or those obtained by other methods.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030404
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  • 20
    Electronic Resource
    Electronic Resource
    A model for atomic mixing (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 157-169 
    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 is concerned with the theoretical determination of the amount of atomic mixing which accompanies the erosion of a solid surface exposed to an energetic ion beam. The work is relevant to sputter depth profiling where such mixing complicates the deduction of the initial depth distributions from the measured ion yields.A mathematical model, which considers the effects of incident ion accumulation, ballistic relocation and diffusion is described. The governing integro-differential equations are solved numerically.Results for a GaAs-AlGaAs multi-layer structure bombarded with O2+ ions are compared with results obtained experimentally.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030210
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  • 21
    Electronic Resource
    Electronic Resource
    A hybrid moment-ray-mode method for wave scattering from an aperture coupled system (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 171-182 
    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: Wave scattering from an aperture coupled system is studied using a new method which combines the hybrid ray-mode method and method of moments. The latter is used to formulate the coupling process and the former to provide the Green's function of a parallel plate waveguide. Following standard procedures of the method of moments, we first formulate a system equation for field distributions across the aperture. By expressing these unknown distributions in terms of appropriate basis functions and choosing appropriate weighting functions, the system equation is then reduced to a matrix equation which is solved numerically. In the system of equations, one needs to compute the Green's function of the waveguide for various arrangements of locations of source and receiver. The hybrid ray-mode formulation is best suited for this purpose because it combines rays and modes self-consistently to optimize the advantages of each. The efficiency of the ray-mode Green's function makes use of the moment method practical in waveguides, and the flexibility of the moment method permits application of the Green's function considered to arbitrarily shaped and placed apertures. Numerical implementation illustrates these aspects.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030302
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  • 22
    Electronic Resource
    Electronic Resource
    Combined fine-coarse mesh transmission-line modelling method for diffusion problems (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 111-126 
    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 paper presents a combined fine-coarse mesh TLM method. This technique reduces the memory storage and the computational time when modelling complex structures. In the combined fine-coarse mesh model, the region of interest is covered with a set of transmission-line fine meshes. The remaining part is covered with regular (or irregular) coarse meshes. The fine-mesh nodes are connected through busbars to the adjacent coarse-mesh nodes. The combined fine-coarse mesh TLM technique is applied to some diffusion problems. Significant savings in computational time and memory storage are obtained without loss of accuracy.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030207
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  • 23
    Electronic Resource
    Electronic Resource
    Masthead (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990) 
    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.1660030301
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  • 24
    Electronic Resource
    Electronic Resource
    The modelling of surface evolution during growth and erosionInvited Review. (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 137-155 
    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: When the erosion or growth of a surface that occurs in semiconductor device processing can be considered as everywhere continuous in space and time, the equations of motion of the surface may be specified and determined numerically using a kinetic model of surface evolution. In this review the fundamental concepts of the kinematic model of surface evolution are discussed. Detailed consideration of the theory of characteristics reveals its limitations which are overcome by recent theoretical development based on the Huygens principle of wavefront reconstruction. Correct interpretation of the nature of the basic wavelet, coupled with contemporary ideas of surface and edge propagation, form the essence of a new numerical algorithm. Numerical analysis and consequent numerical procedures derived from the generalized kinematic model are presented. Examples of surface evolution, with particular reference to ion beam induced erosion are given to show the advantages and potential of the method as opposed to existing models and theoretical prediction.When evolution processes are discontinuous and localized, other approaches, particularly those that use numerical modelling, are required. Such approaches are also reviewed here.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030209
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  • 25
    Electronic Resource
    Electronic Resource
    Noise analysis of linear microwave circuits (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 287-315 
    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 fundamentals of computer-aided noise analysis of linear noisy microwave circuits are presented. The method is based on the description of noisy networks by correlation matrices, and allows the noise analysis of linear circuits of general topology exhibiting arbitrary correlations between the noise sources. The description of linear noisy networks by correlation matrices in different representations, the interconnection of noisy networks and the nodal analysis of noisy networks are treated. The correlation matrices of circuits or subcircuits exhibiting thermal noise may be calculated directly from its admittance matrix. The application of the method for the noise analysis of linear microwave amplifiers is discussed.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030408
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  • 26
    Electronic Resource
    Electronic Resource
    Masthead (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990) 
    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.1660030101
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  • 27
    Electronic Resource
    Electronic Resource
    Concurrent processing: The key to rapid probabilistic potential methods (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 1-9 
    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 shows how probabilistic potential methods based on the Monte Carlo approach can be efficiently mapped onto an array of concurrent processors and how the resulting algorithm can provide rapid solutions of harmonic function problems. The method described here exploits the natural concurrency of the Monte Carlo approach. Computation is achieved by use of a low-cost array of transputers linked to a PC-AT. The resulting methodology is powerful and the ideas suggested should have application to many other modelling techniques used for field modelling.A microstrip geometry is used as the discussion vehicle throughout this paper. This geometry was selected since it exhibits a number of the important topological features required in a general problem, e.g. Dirichlet boundary conditions and mixed dielectric. The design of the parallel algorithm used is discussed in detail, and typical results are given.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/jnm.1660030102
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    Planar analysis of radial-line power dividers (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 23-31 
    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 resonant mode field expansion technique presented in previous papers to analyse one- or two-port microstrip structures of different geometrical shapes is now applied to multiport radial lines. In particular, a radial-line n-way power divider is considered. This device allows, under certain hypotheses, an equiphase and equiamplitude splitting of an input signal. The Z matrix formulation has been derived and utilized to obtain the scattering parameters for the circuit. The numerical results are in good agreement with both experimental and theoretical data presented in the literature. The low number of resonant modes required to obtain satisfactory numerical convergence allows a substantial reduction of the computing time with respect to other more complicated approaches.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030104
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    Numerical aspects of the boundary residual method (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 57-71 
    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 boundary residual method is a powerful technique for solving EM boundary-value problems. This technique produces matrices difficult to solve using many of the standard numerical techniques. This paper discusses lesser-known numerical aspects of this method, and it shows efficient and well-conditioned methods to solve both the homogeneous and non-homogeneous boundary residual problem.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030107
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    Analysis of acoustic radiation patterns of array transducers using the TLM method (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 39-56 
    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 paper describes the application of the TLM numerical method for the analysis of acoustic wave propagation. It presents a general scattering algorithm for modelling homogeneous and inhomogeneous mediums where both the density and compressibility of the propagation space are varied. The method is used to obtain the acoustic radiation patterns of discrete transducer arrays. The effect of the spacing and the number of transducer elements on the radiation pattern are demonstrated by numerical results obtained using a two-dimensional TLM mesh. The results also show the effect of array shading on the radiation pattern. Beam steering by delayed excitation of the transducer elements is also demonstrated here. In addition the paper presents two simple techniques for detecting the direction of wave propagation in the TLM mesh.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030106
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    Numerical techniques for microwave and millimeter-wave passive structures. Editor T. Itoh, John Wiley and Sons, 1989, 707 pages. Price £58.50. ISBN: 0-471-62563-9 (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 73-73 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030108
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  • 32
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    Masthead (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990) 
    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.1660030201
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  • 33
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    Non-linear diffusion in process modelling (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 79-90 
    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 non-linear diffusion mechanism arising in process modelling is analysed via a model problem. Using a scaling of the dopant concentration and an adaptive finite element method, high resolution is obtained in a particularly economical way.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030204
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  • 34
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    Estimation of parameters in numerical modelling of non-linear diffusion in semiconductors (1990)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 3 (1990), S. 99-110 
    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 procedure is described for estimating various parameters governing the diffusion of impurities in semiconductors; these parameters are required for a number of explicit numerical models of non-linear diffusion in III-V crystals. The method is based on an analytical solution of the continuum equivalent of a discrete numerical model due to Zahari and Tuck and provides a systematic procedure for analysing experimental data to yield predictions for the coefficient of diffusion of the impurity, the coefficient of self-diffusion of the host material, the bulk equilibrium vacancy concentration and, under conditions of “dissociation” pressure, the surface vacancy concentration. Application of the procedure to two sets of independent experimental data provided reasonably consistent values of the parameters.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660030206
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  • 35
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    Rate-equilibrium LFER characterization of transition states: The interpretation of α (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 1-8 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of substituents on the rate of a reaction and the effect of the same substituents on the equilibrium can often be related by a linear free energy relation (LFER): log k- = α log K= + constant, where k+ and K= are the rate constant and the equilibrium constant, respectively. This review, concentrating on group transfers, adds to many studies describing the use of α to describe the transition state. Although the use of α to describe transition states is general, group transfers constitute a simple class allowing a fairly complete description yet illustrating two often neglected contributions. Group transfers can be described by the Marcus equation relating rate to an average identity rate and the equilibrium constant; a major contributor to the slope, α, of the rate-equilibrium LFER is the variation of identity rates with substituent, rather than reflecting product-like character. Substituent effect LFERs are predominantly attributable to interaction of charges with the substituent. However, α is not an exact measure of the charge on the substituent-containing group, because in a transition state, but often not in a reaction product, there are more remote centers of charge which exert a smaller attenuated effect. A simple treatment of this attenuation for group transfers is proposed. The possibility of application of these ideas to proton transfer reactions and the interpretation of the Brønsted α (or β) is proposed.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030102
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    Maximally inhibited elimination of kinetics of (2-bromoethyl)benzene and 1-bromo-3-phenylpropane in the gas phase. Anchimeric assistance of the phenyl group (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 77-80 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The gas-phase elimination kinetics of (2-bromoethyl)benzene and 1-bromo-3-phenylpropane were studied in a static system and seasoned vessels over the temperature range 390-450 °C and the pressure range 32-104 Torr. The reactions, under maximum inhibition of 4-fold pressure of the free-radical suppressor cyclohexene and/or propene, are homogeneous, unimolecular and obey a first-order rate law. The rate coefficients are given by the following Arrhenius equations: for (2-bromoethyl)benzene, log k1 (s-1) = (13·04 ± 0·10) - (210·8 ± 1·3) kJ mol-1 (2·303RT)-1, and for 1-bromo-3-phenylpropane, log k1 (s-1) = (14·09 ± 0·27) - (227·7 ± 3·6) kJ mol-1 (2·303RT)-1. The phenyl group of (2-bromoethyl)benzene appears to provide anchimeric assistance in the HBr elimination of this compound. However, neighbouring C6H5 participation at the 3-position in 1-bromo-3-phenylpropane for a C-4 conformation is apparently absent. The mechanisms of these reactions are discussed.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030203
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    Hydration of 2,2-dichloro-1-arylethanones in water and tetrahydrofuran-water mixtures (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 89-94 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The hydration of 2,2-dichloro-1-arylethanones was studied in water and tetrahydrofuran (THF)-water mixtures and the equilibrium constants in water were estimated for four ethanones. The process is subject to specific acid and to general base catalysis. The proton inventory technique was applied to the study of the reaction in L2O and THF-L2O solutions (L = H or D). In pure water and water-rich mixtures, a very large number of protons participate in the open transition state, this number decreasing gradually with increasing water content in the mixture, until the minimum value of 2 is reached, corresponding to a cyclic, closed transition-state structure.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030205
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    Additivity of bond separation energies of hydrocarbons and their thermochemical data (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 126-134 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The additivity of experimental bond separation energies is demonstrated. This thermodynamic function can be reproduced by summation of group equivalents with a correction for the ‘stabilization’ energy. For this purpose, several group equivalents have been developed for alkanes and alkenes. The correlation between the computed and the experimental bond separation energies is good. These equivalents are then used in evaluating the stabilization (destabilization) energies for aromatic hydrocarbons and polyenes. The results obtained are in good agreement with values reported in the literature.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030209
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  • 39
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    Kinetic and spectroscopy of 2-naphthylphenylcarbene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 135-138 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2-Naphthylphenylcarbene (2-NPC) was studied by low-temperature EPR spectroscopy and by solution-phase laser flash photolysis. 2-NPC was found to have a triplet ground state with two distinct rotomeric forms. The triplet carbene was found to react with methanol, 1,1-diphenylethylene, styrene, carbon tetrachloride, isoprene, toluene and 2-methyltetrhydrofuran.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030210
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    Stereochemical studies. XXXIVPart XXXIII, I. G. Mursakulov, V. A. Svyatkin, V. V. Samoshin, N. S. Zefirov, Zh. Org. Khim. 22, 773-776 (1986).. Quantitative description of ring puckering via torsional angles. The case of six-membered rings (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 147-158 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The quantitative description of ring puckering suggested by the authors is compared with that of Cremer and Pople. The applicability of both methods is discussed for the case of six-membered rings with the use of model calculations simulating various ring distortions and with the analysis and comparison of puckering parameters computed on the basis of x-ray data for 40 six-membered rings in different cyclic structures. The 2N times reduction of the field of variation of puckering parameters for the N-membered ring is suggested and the algorithm for the renumbering of the ring atoms for this purpose is described for six-membered rings.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030304
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  • 41
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    Deuterium fractionation factors for carbon-hydrogen bonds: Calculations using scaled quantum-mechanical force constants (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 181-189 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The determination of uniform scaling factors for force constants calculated at the STO-3G and 4-31G levels of ab initio SCF MO theory is described; scaled 4-31G force constants provide reasonable estimates of reduced partition function ratios for deuteriated/protiated molecules. Gas-phase deuterium fractionation factors relative to methane calculated using scaled 4-31G force constants are, however, consistently too high, whereas those obtained by the MP2/6-31G* and scaled STO-3G methods are inconsistent. Scaled 4-31G deuterium fractionation factors relative to water for a range of structural moieties correlate linearly with experimental aqueous-phase values, but are also consistently overestimated. Substitution at a hydrogen-bearing carbon atom affects the deuterium fractionation factor through the combined effect of changes in reduced mass and changes in force constants other than for CH stretching.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030307
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    The decay of 2-phenyl-1,3-dioxolane-2-ylium salts in solution (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 195-199 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The decay of 2-phenyl-1,3-dioxolane-2-ylium salts in 1,2-dichloroethane solution has been studied by means of 1H NMR and UV spectroscopy and conductimetry. The influence of the nature of the anion (SbCl6-, SbCl5Br-, AsF6-) and of the methyl substituents on the rate constants of decay is discussed.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030309
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030401
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    Photochemical electrocyclization of the allyl radical into the cyclopropyl radical (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 219-229 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Following the observation that allyl radicals trapped in an argon matrix can be photolytically converted into cyclopropyl radicals (λ = 410 nm, 18 K), the IR spectrum of the cyclopropyl radical was recorded for the first time and interpreted. Bicyclopropane and cyclopropane are formed when the photolysed argon matrix is warmed from 18 to 35 K. The identification of these new species unequivocally proves the presence of cyclopropyl radicals in the photolysed matrix. This radical is shown to be a σ-type (Cs symmetry) and not a π-type (C2v symmetry) radical; of the 18 normal frequencies of the Cs cyclopropyl radical, all active in the IR, 16 were observed and were assigned to their corresponding normal modes. For this assignment advantage was taken of ab initio frequency computations reported in the literature and performed by the authors.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030403
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  • 45
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    Organophosphorus herbicides and plant growth regulators part 1. Synthesis and protonation behaviour of glyphosate and related compounds (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 248-254 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ionization constants of N-phosphonomethylglycine (glyphosate) and three structurally related plant-growth regulators were determined by potentiometric titration. The effect of pD on the chemical shifts of the 1H and 13C nuclei of the methylene groups and of the 31P nucleus in these substrates was measured by NMR spectroscopy. The results allowed an assignment to be made of a specific site (carboxylic, phosphonic, ammonium) in the molecule to each of the determined pKa values.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030407
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  • 46
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    Concentration-dependent deuterium isotope effects on the quantum yield of arene-alkene meta photocycloaddition: The role of excimers (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 273-278 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A deuterium isotope effect on the arene-alkene meta photocycloaddition, reported earlier for toluene/toluene-d8 photoaddition to cyclopentene, was found to depend on the concentration of both arene and alkene. This phenomenon is explained in terms of an unbalanced dissociation of ‘mixed’ excimers, which play a role in the intermolecular competition experiments.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030411
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    Mechanism of α-substitution reactions of acrylic derivatives (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 285-288 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reactions between acrylic esters, nitriles and similar compounds on the one hand and aldehydes and ketones on the other, catalysed by tertiary amines, lead to α-(hydroxyalkyl)acrylic compounds. Evidence on the basis of kinetics, volumes of activation and of reaction, and kinetic isotope effects is presented to deduce a mechanism in which amine first undergoes Michael addition, the resulting enolate ion adds to the carbonyl compound in a rate-determining step and finally base is eliminated. An analysis of the solvent effect on rates is also presented.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030503
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    [4]Paracyclophane: MNDO and STO-3G molecular structure and strain energyTaken in part from Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 295-300 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The molecular structure of [4]paracyclophane was optimized at the semiempirical MNDO and the ab initio STO-3G level. A comparison of the results showed that the benzene ring is much less bent at the STO-3G level. Although some bond alternation is predicted at both levels of theory, the aromatic carbon-carbon bond lengths are still in the range typical of highly delocalized compounds. The calculated strain energy [SE(tot.)] of [4]paracyclophane is larger for the STO-3G structure. Nevertheless, the distributions of SE(tot.) over the bent benzene ring [SE(bb.)] and the oligomethylene bridge [SE(br.)] are the same for the MNDO and STO-3G structures.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030505
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    Configurations and dipole moments of O-substituted hydroximoyl cyanides. Stereoelectronic effects in the ground state of oximino compounds (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 316-324 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dipole moments of the Z and E isomers of O-methylbenzohydroximoyl cyanides [ArC(CN)=NOCH3, Ar = C6H5 and 4-NO2C6H4], the Z isomers of benzohydroximoyl cyanides [ArC(CN)=NOH, AR = C6H5 and 4-NO2C6H4] and the Z isomers of O-benzoylbenzohydroximoyl cyanides [ArC(CN) = NOCOC6H5, Ar = C6H5 and 4-NO2C6H4] were measured. An analysis of these dipole moments indicates that anti delocalization from the OCH3 (OH) group has a small but significant effect on the overall direction and magnitude of the dipole moment. Semi-empirical molecular orbital calculations at the MNDO level support this proposal. The x-ray crystal structure of (Z)-O-methyl-p-nitrobenzohydroximoyl cyanide was carried out to confirm the configuration of the compound.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030508
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030601
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    Stereochemistry and kinetics of thiophenoxide ion addition to methyl para-substituted phenylpropiolate derivatives in methanol. I (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 375-378 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of a series of methyl para-substituted phenylpropiolates with thiophenoxide ion in methanol were studied and their rates measured. Methyl β-thiophenyl esters were obtained as mixtures of Z and E isomers and their configurations were established by 1H NMR spectroscopy. Good Hammett correlations with ρ values of 1·57-1·97 were obtained, which suggest a carbanionic character of the transition state. A stepwise mechanism proceeding via an intermediate carbanion is postulated for this non-sterospecific addition reaction.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030605
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    Structural studies of halogen adducts of diorganyl chalcogenides in solutions by 1H, 13C, 77Se and 125Te NMRFor a preliminary contribution, see Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 358-368 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1H, 13C, 77Se and 125Te NMR spectra were measured for several sulphides, selenides, tellurides and their halogen adducts to establish the criteria for distinguishing trigonal bipyramidal (TB) adducts from molecular complexes (MCs). TB formation caused large downfield shifts for methyl protons and methyl, ipso and para carbons of methyl and phenyl selenides and tellurides. Large downfield shifts (〉 100 ppm) were also observed for selenium and tellurium by the formation of TB from the parent selenides or tellurides. The plots of the 125Te vs 77Se chemical shifts for a set of corresponding compounds gave a straight line with a slope of 1·74, showing that the linear relationship holds well for tellurides and selenides and their TB adducts examined in this work. Upfield shifts of the ipso carbons were characteristic of MC formation. The para carbon signals of MC appeared downfield relative to those of the parent selenides, although the shift values were not so large. The 77Se signals for MC shifted slightly downfield (≤ 10 ppm). The dissociation constants for iodine adducts of dimethyl selenide and selenoanisole were determined. The MC structure of bromine adducts of sulphides is well demonstrated on the basis of the criteria set out. 1H and 13C NMR spectra of ethylbenzene and ethers were also recorded in the presence of iodine or bromine. However, their chemical shifts were the same as those in the absence of iodine or bromine, within experimental errors.
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    Reaction of aryliminodimagnesium with diphenyl diketones: Heat evolution accompanying single electron transfer and chelate formation, and product distributionAryliminodimagnesium Reagents Part XVII. For Part XVI, see Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 379-389 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reaction of diphenyl diketones (benzils) with aryliminodimagnesium [ArN(MgBr)2, IDMg], a magnesium reagent having condensation ability, was investigated. By comparison of the relative amounts of heat evolved in the reactions of IDMg (mildly electron donating) and ArMgBr (strongly electron donating) with some carbonyl and nitro compounds, results were obtained supporting the reported correlation of the relative yields of normal and abnormal (radical) products with single electron transfer (SET) efficiency estimated by the oxidation and reduction potentials of reactants. A sole exceptional result, i.e. the great heat evolution caused by the combination of benzil and IDMg, was attributed to the generation of tightly chelated radicals via SET. The involvement of stepwise SET was confirmed by ESR. On the basis of these results, substituent effects of benzil and mono-condensation products on their reduction potentials and on the relative yields of normal (mono- and di-condensation) and abnormal (dimerization) products were examined. All the results were consistently explained in terms of the relative efficiency of chelation (or σ-complexation) and SET in two main processes. The role of the initial stages involved in the processes governing the final product distribution is discussed.
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    Correlations of rate and selectivity of a Diels-Alder reaction with Sp parameters (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 414-418 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rate and endo/exo selectivity of the Diels-Alder reaction between cyclopentadiene and methyl (E)-α-cyanocinnamate at 25°C, in several acetone-water and 1,4-dioxane-water mixtures, were measured. The linear correlations of log k and log(endo/exo) vs solvophobicity are reported. Correlations for selectivity are considerably improved when the results obtained in acetone-water and 1,4-dioxane-water are taken as separate series.
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    Substituent effects in the solvolysis of benzyl tosylates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 449-455 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The substituent effect on the rates of solvolysis of substituted benzyl tosylates in acetic acid was analysed based on the Yukawa-Tsuno LArSR equation. Neither the LArSR nor simple σ+ treatment was capable of providing any linear correlation plot for the full range of substituents. The σ+ plot was not simply bilinear but widely scattered, giving a split pattern of parallel curves with significant gaps. Since any mechanistic transition with substituents should bring about a single continuous curve when plotted against an appropriate substituent constant scale, the split σ+ plot is not in line with an interpretation in terms of a mechanistic transition. On the other hand, the LArSR plots with r = 1·3 coalesced into a single smooth curye including the meta correlation curve. A different resonance demand as high as r = 1·3 is required in order to give a smooth single-curve correlation for the entire substituent range without splitting. For the reactive substituents down to p-halogens, a sufficiently linear plot can be obtained against a set of substituent constants with r = 1·3 which can be referred to the substituent effect correlation for the kc mechanism of this system. An identical r value was likewise assigned for the kc mechanism of the hydrolysis for a more severely restricted range of activating substituents down to the 4-MeS-3-CN group.
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    N-Carbeniopyridinium salts: Charge-transfer complexes with the C5 (COOMe)5 anion; C—C bond formation with the TCNQ radical anion (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 459-469 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: N-[2,3-Bis(dimethylamino)cyclopropenylio]- and N-(tetramethylamidinio)pyridinium salts (trifluoromethanesulphonates and tetrafluoroborates) form 1:1 and 1:2 charge-transfer complexes with the pentakis(methoxycarbonyl)cyclopentadienide anion. The x-ray crystal structures of 1-[2,3-bis(dimethylamino)cyclopropenylio] pyridinium pentakis(methoxycarbonyl)cyclopentadienide tetrafluoroborate hydrate and of 1-[2,3-bis(dimethylamino)cyclopropenylio] pyridinium bis[pentakis(methoxycarbonyl)cyclopentadienide] were determined. In constrast, the tetra-cyano-p-quinodimethane (TCNQ) radical anion reacts with the first-mentioned salts by C—C bond formation to give novel dicationic salts. Thereby, the radical anion attacks the pyridinium γ-position of the N-(tetramethylamidinio)-pyridinium dication, but the three-membered ring of the N-[2,3-bis(dimethylamino)cyclopropenylio] pyridinium system.
    Additional Material: 6 Ill.
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    Evidence for formation of 2-nitrobenzoylperoxy radical generated from 2-nitrobenzoyl chloride and superoxide: Spin trapping of the peroxyradical intermediate and its oxidizing abilities (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 482-484 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2-Nitrobenzoyl chlorde was reacted with superoxide in acetonitrile to form 1 2-nitrobenzoylperoxy radical intermediate which showed a stronger oxidizing ability than that from superoxide, as confirmed by ESR spin trapping studies.
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    Kinetics and mechanism of acid hydrolysis of 2-carboethoxypyridine N-oxides (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 489-492 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rate constants and activation parameters have been measured for the acid hydrolysis of six 2-carboethoxypyridine N-oxides. The correlations of log kobs. vs Hammett's constants and chemical shifts of intramolecular hydrogen-bonded protons in parent acids are analysed. Evidence was found for the participation of intramolecular hydrogen bonding in the hydrolysis of the esters.
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    URL: http://dx.doi.org/10.1002/poc.610030802
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    Origin of exo selectivity in norbornene. An ab initio MO study (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 519-533 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The geometries of the reactants, the reactant π-complex, the transition state and the product for exo and endo addition of BH3 to norbornene were optimized at the HF/3-21G level, and their energies were calculated at the MP2/6-31G level. The analysis of activation energy and model calculations singled out the endo deformability, a major portion of the norbornene deformation energy, as the origin of exo selectivity; norbornene, with the olefinic hydrogens already bent toward endo in the equilibrium geometry, requires less deformation to reach the exo than the endo transition state. The reason why olefinic hydrogens are bent in norbornene has been elucidated. An analysis indicates that the difference between norbornene exo side and bicyclo [2.2.1] hex-2-ene is also dictated by the endo deformability.
    Additional Material: 10 Ill.
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030901
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    Interpretation of 1H NMR spectra of 2-benzopyrylium salts with the use of the CNDO/2 method (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 575-580 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 1H NMR spectra of eleven substituted 2-benzopyrylium salts are interpreted with the aid of the CNDO/2 method for standard geometry. Some effects of the substituents are considered for the charge distribution in the 2-benzopyrylium cation.
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    Frequency-dependent branching ratio in the infrared multiphoton photochemistry of diethyl carbonates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 567-574 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Unimolecular decomposition of 0·1 Torr of diethyl carbonate, diethyl-d5 carbonate and diethyl-d10 carbonate induced by irradiation with a CO2 TEA laser was investigated. In all cases only ethylene, ethanol and CO2 were obtained. In the case of diethyl-d5 carbonate, both ethylene-d4 and ethylene-d0 were observed together with the corresponding isotopic variants of ethanol. The chemical branching ratio was determined as a function of irradiation frequency and laser fluence by analysis of the ethylene-d0/ethylene-d4 ratio. RRKM theory applied to the branching ratio data requires very different average energies for two sets of fluence and frequency conditions that give identical total yields.
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    URL: http://dx.doi.org/10.1002/poc.610030903
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    NMR spectroscopic study of configurations and conformations of 5-pyridylmethylenehydantoins (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 559-566 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nine 5-pyridylmethylenehydantoins were prepared. Each of the 1-methyl-substitute compounds was obtained in two stereoisomeric forms. Only one form of each of the 3-methyl-substituted and N-unsubstituted compounds was obtained directly from synthesis but could be partially converted into the other stereoisomer photochemically. The Z/E configurations and the conformational relationship between the pyridine and hydantoin rings were studied by 1H and 13C NMR spectroscopy, including variable-temperature 1H NMR. The existence of N—H…N or C—H…N interactions and the possibility of tautomerism are suggested for some of the compounds. The Z-isomers of compounds with 2- or 3-pyridyl rings prefer an s-cis conformation whereas the E-isomers prefer an s-trans conformation.
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    Borohydride reduction of alkyl phenyl ketones within a reversed-phase liquid chomatographic column (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 594-598 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reductions of propiophenone and octanophenone to 1-phenylpropan-1-ol and 1-phenyloctan-1-ol, respectively, with sodium borohydride and tetrabutylammonium borohydride were performed on a reverse-phase highperformance liquid chromatographic (HPLC) column of macroporous 10-μm poly(styrene-divinylbenzene) undr HLPC conditions. In these reactions a lower concentration of tetrabutylammonium borohydride than of sodium borohydride was needed to effect the same extent of reduction, and modest substrate selectivity was obtained.
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    URL: http://dx.doi.org/10.1002/poc.610030907
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    Electronic absorption spectra of aliphatic diamine radical cations. Conformation-dependent charge delocalization (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 606-610 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Electronic absorption spectra of radical cations generated by steady-state and pulse radiolysis from a series of α,ω-diaminoalkanes (R2N(CH2)nNR2; n = 1-6, R = CH3 or C2H5), 1,4-dimethylpiperazine and 1,4-diazabicyclo [2.2.2] octane (DABCO) were measured. In some cases spectral evidence was obtained for an interaction between the nitrogen atoms leading to charge delocalization in the radical cation. A delayed formation of radical cations was associated with a conformational change necessary for achieving the most stable structure having a favourable conformation for charge delocalization.
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    General-acid, specific-base and intramolecular catalysis of the dehydration step in nitrone formation from furfurals and phenylhydroxylamine (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 620-626 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nitrone formation from furfural and 5-nitrofurfural with phenylhydroxylamine was studied in water at 25°C and ionic strength 1·0 (KCl). The reaction exhibits general acid catalysis (α = 0·52), specific base catalysis and a pH-independent process. The results are consistent with a mechanism where dehydration of an N,N′-dihydroxy addition intermediate, formed by a rapid pre-equilibrium, is the only rate-determining step over the pH range studied (1-11). In contrast, nitrone formation from p-chlorobenzaldehyde and N-methylhydroxylamine exhibits a clear change of rate-determining step, from dehydration of the addition intermediate to attack of the nucleophile on the aldehyde, with increase in pH. The profile of log k2 (k2 = second-order rate constant) vs pH indicates, by comparison with the corresponding profile for similar reaction, that phenylhydroxylamine exhibits unexpected nucleophilic behaviour in this reaction. The pH-indpendent dehydration process, which has a higher rate constant than that predicted from the Brønsted line for the water catalysis, appears to involve intramolecular catalysis rather than bifunctional catalysis by water.
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    Rearrangement and cyclization in the ionization of the 4-chloro-3-methylbutanoyl cation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 639-642 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The second ionization of the 4-chloro-3-methylbutanoyl ion forms a primary alkyl acyl dication, as a tight ion pair. Methyl and hydrogen shifts occur to comparable extents indicating that the relative stability of the product (sec- or tert-carbocation) does not influence the energy barrier for the shift. The product of methyl shift (1,3-sec-alkyl acyl dication) loses the proton closest to the counterion in the tight ion pair and forms the pent-3-enoyl cation. Protonation-deprotonation of the latter, followed by internal acylation, gives the protonated cyclopent-2-enone. The dication resulting from hydrogen shift loses a proton from C-2 and gives the 3-methylbut-2-enoyl cation.
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    Electrochemical and photoelectronic spectral study of compounds with high ionization potentials: Anodic oxidation of vinyl triflates in aprotic solvents (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 670-676 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Microelectrodes can be used to measure redox half-wave potentials in aprotic solvents containing no purposely added supporting electrolyte. By employing an electrode of sufficiently small size, the accessible potential range in solution is considerably extended. The electrochemical oxidation of vinyl (enol) triflates, which are oxidized at high electrode potentials, can therefore be studied using an ultramicroelectrode. Oxidation and ionization potentials, determined by ultramicroelectrode voltammetry and He I photoelectron spectroscopy, respectively, of 2-methylprop-1-enyl, cyclohexenyl, cyclopentenyl, 1,1-diphenylethenyl and prop-2-enyl triflate are reported. The results from electrochemical measurements and photoelectron spectra were compared.
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    Micellar catalysis of organic reactions. 28For Part 27, see T. J. Broxton and R. P.-T. Chung, J. Org. Chem. 55, 3886 (1990).. A comparison of the catalytic effects of micelles containing bromide and fluoride counterions on some SNAr AND BAc2 reactions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 677-683 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The catalytic effects of micelles of cetyltrimethylammonium bromide (CTAB) and fluoride (CTAF) on several SNAr and BAC2 reactions were studied. Rate versus detergent concentration curves predicted by the pseudophase models PPIE (ion exchange) for CTAB studies and PPMA (mass action) for the CTAF studies were fitted to the experimental results to determine the best values of the substrate binding constant (Ks), the second-order rate constant for reaction in the micelles (K2M) and the exchange constant KOH/X (PPIE) or binding constant (PPMA) for the counterions. Better catalysis by micelles of CTAF is shown to be due to the combined effects of a more favourable exchange constant in CTAF than in CTAB, slightly different rates of reaction within the two micelles and different values of β, the fraction of micellar head groups neutralized in CTAF and in CTAB.In both micelles the magnitude of catalysis depends on the charge produced in the intermediate complex and the presence of electron-withdrawing groups to stabilize that charge. Strongest catalysis was found for a reaction leading to a monoanionic intermediate complex in which the charge was stabilized by two nitro groups, and the weakest catalysis was found for a reaction leading to a dianionic intermediate in which no electron-withdrawing groups were present.
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
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    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.610031101
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    Comparison between some semi-empirical and ab initio Hartree-Fock models for the description of amides (formamide revisited) (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 711-722 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A comparative study on the use of the MINDO/3, MNDO and AM1 semi-empirical methods for the description of formamide and aliphatic amide systems is reported. For formamide, ab initio Hartree-Fock calculations are also reported using both the STO-3G and 3-21G basis sets, as well as a basis set obtained by a minimal relaxation of the STO-3G contraction scheme. It is shown that both the MNDO and the STO-3G methods cannot properly reproduce the experimental results. In both cases this appears to be due to inadequacies of the basis sets used. Again in both cases only small improvements in the basis set necessary to allow for the diffuse character of the pπ orbitals lead to dramatic improvements in the calculated results. In the case of the STO-3G basis set this is demonstrated by the fact that a small relaxation in the contraction leads to results even superior to those with the 3-21G set. The conclusions reached for amide systems can be extended to other systems where planarity around or inversion with respect to nitrogen is an issue. This is demonstrated for ammonia.
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    Absolute rate constants for the reactions of phenylhalocarbenes with alkynes (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 760-763 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Additions of phenylchlorocarbene and phenylfluorocarbene to representative alkynes are rapid (106-107 l mol-1 s-1). The variation of the rate constants with alkyne structure parallels that observed with analogous alkene substrates. The addition of phenylchlorocarbene to 3-hexyne is characterized by a very low activation energy (∼ 2 kcal mol-1) and a large, negative entropy of activation (∼ -20 e.u.).
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
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    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.610031201
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    Kinetics of oxidation of amino acids by alkaline hexacyanoferrate(III) (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 799-802 
    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 oxidation of α-amino acids (glutamic acid and aspartic acid) by alkaline hexacyanoferrate(III) were studied at constant ionic strength and over the temperature range 323-348 K. The rate was dependent on the first power of the concentrations of substrate and oxidant, but was independent of the concentration of alkali in the range studied. The value of kH/kD was in the range 8·1-8·3 for the slow step, indicating the loss of a hydrogen atom from the C—H bond, giving a radical species which was characterized by ESR spectroscopy. The reaction proceeds by way of the α-imino acid, formed in a fast step, which undergoes hydrolysis to give the corresponding α-keto acid.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031205
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    Solvation of indenyllithium and indenylpotassium studied by 13C NMR spectroscopy (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 9-12 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polarization of the π-electron systems of indenyllithium (In -Li+) and indenylpotassium (In -K+), which is generally indicative of the degree and tightness of contact ion pairing, was investigated by 13C NMR spectroscopy. The effect of changing solvent is about two thirds as great for In -K+ as for In -Li+. The indenyl anion is more strongly polarized with Li+/dimethyl sulfoxide than with Li+/ammonia, whereas the reverse is observed for In -K+. Complexation of In -K+ in tetrahydrofuran (THF) by cryptand(2,2,2) results in a π-electron distribution identical with that of In -Li+ in hexamethylphosphoramide, indicative of solvent- or agent-separated ion pairs or free ions. Small but significant cation-anion interactions are observed for In -K+ in hexamethylphosphoramide and for In -N+Me4 in THF.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030103
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    Structure and stability of 2σ/1σ* three-electron-bonded radical cations from 1,n-bis(alkylthio)alkanes in aqueous solutions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 17-22 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A large number of 1,n-bis(alkylthio)alkanes, R′S(CH2)nSR″, was investigated by pulse radiolysis in aqueous solutions. The sulphur-centred radical cations, which were obtained on oxidation of the dithia compounds by ·OH radicals, are stabilized via 2σ/1σ* three-electron interaction between two sulphur atoms. Intramolecular stabilization is the only process observed for n = 2-4, whereas for longer chain compounds with n 〉 4 some intermolecular sulphur-sulphur interaction is also indicated. The stability and yields of the three-electron-bonded species also depend on the nature of the substituents R′ and R″, and for the intermolecular systems are a function of solute concentration. The results corroborate earlier investigations and demonstrate, in particular, that the optical parameters are a very sensitive measure of changes in electron density and structure of the three-electron-bonded systems.
    Additional Material: 2 Ill.
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    Solvolysis of highly reactive phosphorus-sulphonic anhydrides. Stereochemical and chemical arguments for phosphathiacylium cation formation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 23-34 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The stereochemistry and mechanism of solvolysis of optically active tert-butylphenylphosphinothioic-O-trifluoromethanesulphonate (1) in solvents of different ionizing power were studied. It was found that in solvents of high ionizing power and low nucleophilicity 1 ionizes with the formation of a phosphathiacylium cation (2) as the reaction intermediate. Product resulting from the reaction of 2 with anisole was isolated and characterized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030106
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    Stereochemistry of silver-ion-assisted solvolysis of tert-butylphenylphosphinothioic iodidate. Phosphathiacylium cation formation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 35-37 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies on the stereochemistry of silver-ion-assisted solvolysis of a new optically active tert-butylphenylphosphinothioic iodidate demonstrated that the reaction proceeds with inversion of configuration at the phosphorus atom. Evidence for phosphathiacylium cation formation as a reactive intermediate is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030107
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    Probing of transient photoenol formation from ortho-methyl-substituted phenyl ketones by hydrogen-tritium exchange (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 38-40 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies on the photochemically induced hydrogen-tritium exchange in o-methyl-substituted phenyl ketones are reported. It is shown that the tritium exchange can be beneficial for probing transient photoenol formation, particularly when photochemical side-reactions are occurring.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030108
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    Studies on organophosphorus compounds. XXXVI.For Part XXXV, see S. S. Li, Z. Y. Chen and C. Y. Yuan Scientia Sinica (Series B) 136, (1989).. Substituent effects of alkylphosphonates and -phosphinates in alkaline hydrolysis (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 48-54 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Alkaline hydrolysis of diethyl alkylphosphonates and alkyl diethylphosphinates was studied in aqueous dimethyl sulphoxide. The behaviour of these acyclic phosphorus esters is very similar to that of some cyclic phosphorus esters. Rate constants were measured at three temperatures over a 30°C range, and the activation functions of the reaction were estimated. The basic hydrolytic process was proved to be a bimolecular AE reaction. Multiple regression analyses involving rate constants and substituent parameters gave, as a rule, poor results using steric constants derived from carbon compounds. However, the substituent steric effect on the rate of hydrolysis of phosphonates and phosphinates studied correlated very well with ΔΔE, representing the difference in steric energy calculated by molecular mechanics. It is attributed to the various degrees of susceptibility of carbon and phosphorus atoms to the steric hindrance of the substituents. Moreover, Newman's rule of six for the hydrolytic reaction of carboxylates was completely eliminated in phosphorus ester hydrolysis.
    Additional Material: 2 Ill.
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    The kinetic deuterium isotope effect of proton-transfer reactions in solution. Comparison of the marcus and the quantum-statistical mechanical models (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 62-68 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The free energy dependence of the kinetic deuterium isotope effect of proton-transfer reactions in solution is usually analysed in terms of the Marcus model. By means of modern computer techniques, the more general quantumstatistical mechanical model is also amenable to routine application. The differnces in the basic assumptions of the two approaches concerning the kinetic isotope effect are discussed. Reaction series for which both the Brønsted relation and the free-energy dependence of the kinetic isotope effect are available are analysed by means of the two models using one set of parameters for both free-energy relations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030112
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    Porphyrin-tyrosine interactions: Photo-CIDNP and NMR studies (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 69-76 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Strong 1H and 13C nuclear polarizations are observed when aqueous solutions of synthetic water-soluble porphyrins are irradiated in the presence of tyrosine and some of its derivatives. These polarizations are strongly pH dependent. Evidence is also shown for the formation, in the dark, of a complex between the reactants. The association constants are evaluated from the NMR chemical shifts on the aromatic tyrosine protons induced by the presence of the porphyrins. The nature of the intermediate radical pair generating the CIDNP effects is discussed. An electron-transfer reaction from tyrosine to the excited triplet state of the porphyrin, or within the porphyrin-tyrosine excited complex, is expected to be the primary step in the reaction. It is followed by subsequent proton transfer within the initial ion radical pair. The spin polarizations arise principally from the back-transfer step, as the reactants are the only products which are polarized.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030202
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    Brønsted coefficients and the theory of acid-base catalysis of proton transfers from carbon acids (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 95-109 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intersecting-state model previously used to interpret proton transfers in ground and excited states and enzyme catalysis was applied to the general acid-base catalysis of carbon acids. The results are consistent with the predictions published for these systems and provide a new physical meaning for the Brønsted coefficients. It is shown that in addition to the linear free energy effect, the Brønsted coefficients are also influenced by the tightness of the transition states and by electronic effects. The model suggests that the increased reactivity of carbon acids towards proton transfer in non-hydrogen-bonding solvents is caused by an added electronic effect on the thermodynamics of the reactions. The curvatures of the Brønsted plots are interpreted in terms of an entropic contribution to the position of the transition state.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030206
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    Gas-phase nitration of thiophene and N-methylpyrrole by protonated alkyl nitrates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 110-118 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase nitration of thiophene (1) and N-Methylpyrrole (2) was studied by radiolytic tecniques, supported by chemical ionization mass spectrometry. The substrate and positional selectvities of protonated alkyl nitrtes (CH3NO3H+, CF3CH2NO3H+) were deduced from competitive reactions with bezene performed under different conditions. The apparent kS/kB ratios, which are independent of the pressure and unaffected by the presence of a strong base (NEt3), depend on the nature of the electrophile, passing for 1 and 2 from 7·2 and 6·4, respectively, with CH3NO3H+ to 1·1 and 1·0, respectively, with the more reactive fluorinated caution. Predominant (88%) α-substitution takes place in 1, whereas no appreciable positional discrimination is displaced by 2. The results suggest that the electrophilic attack can also occur a the heteroatom, and point to the same mechanism postulated for gasphase nitration of aromatic substrates, the reactivity being essentially governed by electrostatic interactions within the ‘encounter pair’.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030207
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    15N NMR of nitranions: Opposite shift effects of σ and π charge (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 139-142 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nitranions of pyrrole, aromatic and heteroaromatic amines, carboxamides and pyridyl carbanions are generated by deprotonation either of NH or CH acids. The positive or negative displacements undergone by the 15N nucleus relative to the neutral precursor depend on whether a σ or π charge is increased. They are associated with the symmetry of the nitrogen orbital in which the electron pair is either generated or that to which it is delocalized.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030302
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  • 86
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    syn-anti Isomerism in the 1,3-dipolar cycloaddition to cis-3,4-disubstituted cyclobutenes. 4. Intramolecular interactions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 159-173 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio (4-31G) molecular geometry optimizations on cis-3,4-disubstituted cyclobutenes show that the extent and direction of their ground-state pyramidalization depend on the type of substituents and on whether these substituents are part of a ring condensed on to the cyclobutene moiety. Thus, electron-withdrawing substituents such as Cl and OMe bring about an out-of-plane anti bending of the olefinic hydrogens, whereas cyclobutenes condensed on to small carbocyclic rings exhib high syn bending. Intramolecular interactions are analysed in the frame of a new model where the interactions arise from the energy matrix elements between the hybrid atomic orbitals involved in the different bonds. The analysis is carried out by C-INDO calculations on deformed molecules (with the olefinic hydrogens forced out-of-plane by ± 20°). These latter calculations reveal that non-planarity of the double bond occurs in the direction of increasing interactions between the hybrid atomic orbitals involved in the σ-allylic bonds and in the π-bond. The increase in this kind of interaction can also explain non-planarity in norbornene, 7-oxanorbornene, 5,6-dioxanorbornene and 5,6-dioxabicyclo [2.2.2] oct-2-ene. The results strongly suggest that pyramidalization and the related energy asymmetry of out-of-plane bending of olefinic hydrogens are important factors in governing facial selectivity of 1,3-dipolar cycloadditions to cis-3,4-disubstituted cyclobutenes.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030305
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    Photochemistry of pyridinium salts 1. Intramolecular charge transfer in N-amino-substituted pyridinium cations (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 200-204 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photophysics and photochemistry of N-amino-substituted pyridinium salts were investigated. Electron transfer from the amino group to the pyridinium ring takes place in the singlet excited state. The fluorescence quenching and photoreactivity of these compounds is conditioned by this process. Irradiation of N-aminopyridinium salts in solution leads to novel fused heterocycles or to triphenylpyridine, depending on the concentration of the initial compound. Free radical intermediates are involved in the photoreaction.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030310
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    Relationship between substituent electronegativity and field parameter in the aliphatic series. Introduction of charge separation parameter (λ) (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 209-218 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The problem of non-proportionality between the substituent field parameter (σF) and substituent electronegativity (Δι or σχ) was clarified by the introduction of the ‘charge-separation parameter’ (λ), which is the component for the direction of the H—X axis of the distance between positive and negative poles of the dipole in the H—X molecule. Thus σF was correlated with Δι or σχ by the equation σF = aΔιλ (or σF = a′σχλ). The above proposal was further supported by performing an energy decomposition analysis for the isodesmic reaction in the isolated molecule system (\documentclass{article}\pagestyle{empty}\begin{document}${\rm X}\raise1pt\hbox{---} {\rm H} \cdots {\rm H}\mathop {\rm N}\limits^ + {\rm H}_3 $\end{document} or X—H…HCO2-) at shorter distances (2·0-4·5 Å). It was further shown that field parameters such as σi, F and σF(theor), and the pKa values in the series of aliphatic acids, and spectral data (UPS and 13C-SCS) were also well correlated with Διλ or σχλ. It is concluded that λ and Δι or σχ are essential parameters for interpreting the electrostatic field effect in aliphatic substituent effects, and that the transmission due to the σ-inductive effect is considered to be not as significant as the field effect after a few bonds away from the substituent.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030402
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    Contrasting kinetic behaviour of allyl and crotyl alcohols towards N-bromosuccinimide in aqueous methanol (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 235-238 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of N-bromosuccinimide (NBS) with allyl and crotyl alcohols in aqueous methanol are first order in NBS. Allyl alcohol displays a zero-order dependence whereas crotyl alcohol exhibits a Michaelis-Menten-type dependence on substrate concentration. The NBS-allyl alcohol reaction is inhibited by H+ whereas the NBS-crotyl alcohol reaction is independent of [H+]. However, both are fast in the absence of acid. The rates are unaffected by the addition of neutral salt and succinimide. The reaction of NBS with crotyl alcohol exhibits a positive dielectric effect whereas allyl alcohol displays no such effect. Inhibition by HgII is observed in the crotyl alcohol reaction but not with allyl alcohol. 3-Bromo-2-methoxypropan-1-ol is the product of the allyl alcohol reaction but a mixture of 2-bromo-3-methoxybutan-1-ol and 2-bromobutane-1,3-diol in the crotyl alcohol reaction. In the allyl alcohol reaction the formation of solvated bromonium ion and of HOBr is suggested as rate-limiting steps. In the crotyl alcohol reaction, rate determining breakdown of an NBS-crotyl alcohol complex, formed in a fast pre-equilibrium, is proposed.
    Additional Material: 5 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030405
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    Anomalous salt effects on a micellar-mediated reaction of bromide ion (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 239-247 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reaction of bromide ion with α-picryl-p-bromoacetophenone (1) is speeded by aqueous cationic micelles of cetyltrimethylammonium bromide (CTABr; C16H33NMe3Br) and dodecyltrimethylammonium bromide (DoTABr; C12H25NMe3Br) and rate constants reach limiting values when 1 is fully bound to micelles of CTABr. Limiting values are not reached in DoTABr, but the data can be fitted to a simple model for the distribution of reactants between water and micelles. Estimated second-order rate constants at the micellar surface are similar to values in water, but this model cannot explain the observed rate enhancements on addition of NaBr to CTABr. Inert anions such as nitrate, mesylate, n-butanesulfonate, phenylmethanesulfonate and camphor-10-sulfonate inhibit reaction in CTABr by competing with Br- at the micellar surface. Other n-alkanesulfonate ions (RSO3-, R = n-C5H11, n-C6H13, n-C7H15, n-C8H17) and arenesulfonate ions (benzene-, toluene-, naphthalene-1- and naphthalene-2-sulfonate) behave anomalously. These ions expel Br- from the micelle, as shown electrochemically, but there are maxima in plots of rate constant against mole fraction of Br-. These rate extrema are apparently due to perturbation of the micellar surface structure that overcomes the inhibition due to competition with Br-. These results show that the simple pseudo-phase, ion-exchange model can be applied only in dilute electrolyte and in the absence of hydrophobic anions.
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    URL: http://dx.doi.org/10.1002/poc.610030406
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    Photostimulated reactions of haloarenes with benzeneselenate ions by the SRN1 mechanism. Competition between electron transfer and fragmentation of radical anion intermediates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 266-272 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photostimulated reaction of p-iodoanisole (p-IAn) and 2-bromopyridine with PhSe- ions in liquid ammonia gave Ph2Se, ArSePh and Ar2Se (Ar = p-anisyl, 2-pyridyl) by the SRN1 mechanism. These products are formed due to the competition between two steps of the proposed mechanism, the fragmentation of the radical anion intermediate formed in the coupling of aryl radicals with the PhSe- ion, and the electron transfer from the radical anion to an electron acceptor. These photostimulated reactions were carried out in different solvents in order to study their influence on the rates of the two competing reactions. They were also studied at high concentrations of p-haloanisoles in acetonitrile (ACN), and it was found that the straightforward substitution product AnSePh was formed only at a 2.5 M concentration of p-IAn, 7·8 M p-BrAn and 15·6 M p-ClAn. The last compound did not react with the PhSe- ion at concentrations as high as 15·6 M, but the substitution reaction took place in the presence of 0·025 M p-IAn (entrainment reaction). The relative reactivity of PhSe- vs PhS- toward 2-quinolyl radicals was studied and it was found that PhSe- reacts 2·7 times faster than PhS- in ACN.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030410
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    Influence of structure on the isomerization of dialkylaminoalkylbenzotriazoles (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 289-294 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The N-1 to N-2 substituent isomerization in a series of 4-methyl and 4,7-dimethyl-N-(α-morpholinoalkyl)benzotriazoles and in 1,5-bis(morpholinomethyl)benzo [1,2-d:4,5-d′] bistriazole was studied and the influence of the structure on this process was evaluated.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030504
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    Destabilized carbenium ions: α-Carbamoyl-α,α-dimethylmethyl cations (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 301-308 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The formation and unimolecular reactions of the especially electron-deficient α-carbamoyl carbenium ions [(CH3)2CCONH2]+ (a1) and [(CH3)2CCON(CH3)2]+ (a2) have been studied by mass spectrometric techniques. The ions a are formed by electron impact-induced dissociation from the relevant isobutyric amides α-substituted by I, Br and Cl, respectively, but the carbonyl protonated methacrylamides b1 and b2 are cogenerated. A similar mixture of ions a and b is obtained by CI(CH4) of the corresponding methacyrlamides. The metastable ions decompose by the loss of CO exhibiting in particular a large kinetic energy release (KER) and by the elimination of NH3 and HN(CH3)2, respectively. It is shown that isomeric ions of structures a and b interconvert prior to decomposition and that the energy barrier separating the isomeric ions is small. Hence the kinetic stability of the tertiary α-carbamoyl-α,α-dimethylmethylcations is reduced compared with other types of α-acyl carbenium ions. This effect can be attributed to the increased proton affinity of the amide group.
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    URL: http://dx.doi.org/10.1002/poc.610030506
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    Electronic Resource
    Theoretical studies of hydride transfer reactions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 325-331 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intersecting-state model (ISM) has been applied to the study of hydride transfer reactions between variously substituted and elaborated pyridinium ions in solution. Chemical bond order is conserved along the reaction coordinate, with a transition state bond order of n≠ = 0·5. This supports the view that these reactions have essentially a synchronous nature and occur by thermal activation over an energy barrier. Tunnelling of H- is negligible because the effective mass for the solvated species is high. Reaction energy and kinetic isotope effects are well accounted for by the model. For reactions in the vapour phase, ISM and the tunnel effect theory show that tunnelling becomes the dominant mechanism. The same is also valid for proton transfers in the vapour phase.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030509
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    AM1 calculations on the tautomerism of free and hydrated hydroxypyridines: Barriers to proton transfer in 2-hydroxypyridine-pyrid-2(1H)-one and effect of solvation and self-association (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 332-338 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: AM1 calculations for the tautomerism of the three isomeric hydroxypyridines are reported and compared with recent ab initio results. Intrinsic stabilities of the various tautomers are predicted by AM1 with an accuracy comparable to or even better than the best available ab initio calculations. Solvation is accounted for by the supermolecule approach and also a continuum model for solvent effects. Except for 3-hydroxypyridine, AM1 correctly accounts for the observed shift of the tautomeric equilibria due to hydration. Energetics of hydrogen bonding are reasonably described by this semiempirical method. With respect to structures, bifurcated hydrogen bonds are preferred by AM1. In addition, for 2-hydroxypyridine and its lactam tautomer self-association in addition to barriers to proton transfer are considered. With respect to tautomerization transition states, AM1 shows serious shortcomings. Compared with both experimental and ab initio results, barriers to proton transfer are considerably overestimated by AM1, especially in the hydrated and associated species. For the dimers AM1 predicts an unsymmetrical transition state which, however, is only slightly lower in energy than the symmetrical structure with two negative eigenvalues of the force constant matrix. Despite several attempts, the transition state for proton transfer in the doubly hydrated species could not be located.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030510
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    Electronic Resource
    Structural studies of halogen adducts of some cyclic selenides and tellurides by 1H, 13C, 77Se and 125Te NMR. Evidence for the formation of molecular complexes of selenoxanthone and selenanthrene with bromineFor a preliminary contribution, see Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 369-374 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1H, 13C, 77Se and 125Te NMR spectra were recorded for selenoxanthone (1a), telluroxanthone (2a), selenanthrene (3a), related compounds and their halogen adducts to elucidate the structure of the adducts in solutions. Although selenides react with bromine to give trigonal bipyramidal (TB) hypervalent complexes in general, 1a reacted with bromine to yield a molecular complex (MC). Its chlorine adduct was found to be a TB. The effective electronegativity of selenium in 1a may be modulated by conjugation with the strongly electron-withdrawing carbonyl group. In the case of 2a, its halogen adducts were TBs. The structure of the bromine adduct of 3a was also demonstrated to be an MC from NMR data.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030604
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  • 97
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    Electronic Resource
    AM1 studies on the acid hydrolysis of acetamide (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 397-403 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The A2 hydrolysis of acetamide was investigated using the AM1 method and the results were compared with those of MNDO. The two methods agree in the general mechanism but differ in detail; MNDO assigns an unduly high energy for a complex with long bonds in contrast to AM1 and ab initio (at the 3-21G and 6-31G levels) methods, which predict a stable structure for such a complex. Inclusion of solvate water molecules has the effect of lowering activation barriers in general. An increase in the number of solving molecules up to four results in narrowing of the activation energy gap between the two rate determining steps of the A2 hydrolysis of the N- and O-protonated acetamide, but no reversal of the relative order of the barrier occurs; the A2 hydrolysis proceeding through the less stable N-protonated tautometer is therefore likely to remain as a major reaction path in solution-phase reactions, in agreement with experimental results.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030608
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    Electronic Resource
    Electronic Resource
    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030701
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  • 99
    Electronic Resource
    Electronic Resource
    Thermochemical data of carbonyl compounds via their bond separation energies (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 443-448 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two types of equivalents for the aldo and the keto groups have been developed, the Schleyer and the bond separation energy (BSE) equivalents. The equivalents were used to give the heats of formation and the BSE of unstrained models. These equivalents were then used in the calculations of the strain energies for aldehydes and ketones. The results obtained were compared with MM2 values. The equivalents were also used in calculations of the stabilization (destabilization) energies for conjugated carbonyl compounds. The results obtained correlate well with the available experimental data.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030705
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  • 100
    Electronic Resource
    Electronic Resource
    Ion association and reactivity of the alkali metal salts of alkanoic acids in dipolar aprotic solvents (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 428-434 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of added alkali metal perchlorates on the rate of lactonization of ω-bromoalkanoate ions was investigated in 99% dimethyl sulphoxide (four-membered ring formation) and in dimethylformamide (DMF) (four- and sixteen-membered ring formation). In all cases the effect of the added metal salts is rate depressing, as a result of the lower reactivity of metal ion-associated species relative to the free ions. Ion-pairing association constants were determined, but the reactivity of ion pairs were so low as to elude direct measurement in most cases. Evidence was also obtained for the formation of ion triplets with Li+ in DMF. The relevance of the present results in connection with the ‘caesium effect’ is briefly discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030703
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