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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2657-2671 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The multistate vibronic dynamics in the X˜ 2E1g-E˜ 2B2u electronic states of the benzene radical cation is investigated theoretically by an ab initio quantum-dynamical approach. The vibronic coupling scheme and the ab initio values of the system parameters are adopted from the previous Paper I. Vibronic line spectra are obtained with the Lanczos procedure. Extensive calculations on wave-packet propagation have been performed with the aid of the multiconfiguration time-dependent Hartree method. Up to five coupled electronic potential energy surfaces and 13 vibrational degrees of freedom have been included in these calculations. As a result, the impact of a third electronic state (X˜ or B˜) on a strongly coupled manifold (B˜-C˜ or D˜-E˜ states) is quantitatively assessed. It leads to a restructuring of the spectral envelope which is stronger for the B˜-D˜-E˜ than for the X˜-B˜-C˜ system. The internal conversion dynamics is characterized by a stepwise transfer of electronic population to the lowest electronic state on a time scale of ∼100 fs, if the system is prepared initially on the highest potential energy surface. Companion calculations have also been performed for the case when the system is prepared in the intermediate state at t=0; they show a branching of the electronic populations. These are all novel findings which are discussed in terms of a series of conical intersections between the various potential energy surfaces. The importance of such multistate vibronic interactions for the photophysics and photochemistry of medium-sized systems is pointed out. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 2377-2388 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple construction scheme for quasidiabatic electronic states implemented earlier for a Jahn–Teller situation [J. Chem. Phys. 110, 9371 (1999)] is extended to the case of a seam of symmetry-allowed conical intersections. It is based on the idea of removing only the singular part of the nonadiabatic coupling elements, leading to the notion of "regularized" diabatic states. Explicit working equations are given for the resulting potential energy matrix which require only information from the adiabatic potential energy surfaces alone. The approach is tested for the photodissociation of H2S and O3 and very good agreement with reference data from the literature is found. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 20 (2001), S. 289-299 
    ISSN: 1434-6036
    Keywords: PACS. 71.45.Lr Charge-density-wave systems – 75.30.Fv Spin-density waves – 72.15.Nj Collective modes (e.g., in one-dimensional conductors – 73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We present a new effect that is possible for strongly correlated electrons in commensurate mesoscopic rings: the collective tunneling of electrons between classically equivalent configurations, corresponding to ordered states possessing charge and spin density waves (CDW, SDW) and charge separation (CS). Within an extended Hubbard model at half filling studied by exact numerical diagonalization, we demonstrate that the ground state phase diagram comprises, besides conventional critical lines separating states characterized by different orderings (e.g. CDW, SDW, CS), critical lines separating phases with the same ordering (e.g. CDW-CDW) but with different symmetries. While the former also exist in infinite systems, the latter are specific for mesoscopic systems and directly related to a collective tunnel effect. We emphasize that, in order to construct correctly a phase diagram for mesoscopic rings, the examination of CDW, SDW and CS correlation functions alone is not sufficient, and one should also consider the symmetry of the wave function that cannot be broken. We present examples demonstrating that the jumps in relevant physical properties at the conventional and new critical lines are of comparable magnitude. These transitions could be studied experimentally e.g. by optical absorption in mesoscopic systems. Possible candidates are cyclic molecules and ring-like nanostructures of quantum dots.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 324 (1982), S. 664-666 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Applications of the Nuclear Overhauser Effect. I. Investigations of the Structure of Z/E Isomeric 2,3-Diarylazetidin-3-olesThe relative configurations of Z/E-isomeric 2,3-diaryl-azetidin-3-oles are determined by mass spectrometry and 1H-n.m.r.-NOE-measurements. The increase of the C(2)-H line intensity by saturation of the OH-signals demonstrates the Z-position of the 2,3-diaryl groups in the isomers 2a.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 325 (1983), S. 881-892 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N.M.R. Spectroscopical Investigations on the Conformational Behaviour of Some 2′ - and 3′-Halogen-substituted Pyrimidine NucleosidesA series of 2′- and 3′-halogenated pyrimidine nucleosides has been synthesized and investigated by 1H, 13C and 19F n.m.r. spectroscopy. The 1H and 13C chemical shifts for the positions 2′ and 3′ depend linearly but oppositely on the substituent electronegativities XR.The conformational equilibrium N ⇌ S of the nucleosides in solution is determined. An approximately linear correlation between the prefered gauche-gauche interaction of the exocyclic CH2OH groups and the ribose N conformation has been found.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 325 (1983), S. 995-1001 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: LIS and X-Ray Investigations of the Structure of 1,5-Diaza-Bicyclo-[3,1,0]-hexanones-(2) Obtained by Irradiation of Pyrazolidone-(3)-azomethineimines1,5-Diaza-bicyclo-[3,1,0]-hexanones-(2) 2 are the photoproducts of pyrazolidone-(3)-azomethineimines 1. Generally they can exist in the exo-form or in the endo-form. 1H-n.m.r.-measurements of 2a-d show that neither at normal temperature (298 K) nor at low temperatures (213 K) an exo/endo mixture is formed photochemically. Therefore the conclusion is drawn that the photoreaction is stereospecific. Chemical shift calculations of the methyleneprotons and the methyl-protons in 2c and 2d using the ring current model and lanthanoide induced shifts (LIS) on 2d with Eu(fod)3 show that in solution the photoproducts have the exo-form. These results are in agreement with results of a single-crystal X-ray structure analysis on 2a.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 323 (1981), S. 914-918 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N,N-Dialkylamides of 2-Hydroxy-2-phenyl-cyclopropan-1-carboxylic Acid - Photochemical Synthesis and Determination of the StructureIrradiation of N,N-dialkylamides of β-benzoylpropionic acid 2a, b in ether by n,π*-excitation leads to the corresponding amides of the hitherto unknown 2-hydroxy-2-phenyl-cyclo-propancarboxylic acid 3a, b, 4a, b. The photocyclization yields diastereomeric mixtures E:Z = 2.5-3:1. The determination of the relative configurations is based on the different tendency of dimerization of the E and Z diastereomers.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 322 (1980), S. 735-741 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 31P-NMR Investigation of N-Aryl-substituted Iminotriphenylphosphoranes: Hammett Relationship between 31P Chemical Shift and Substituent ConstantsThe 31P chemical shifts of p- and m-substituted N-arylimino-triphenylphosphoranes reflect the electronic influence of the substituents and can be correlated by a Hammett relationship. This new correlation was used for the estimation of σ- resp. σ-values for p-(CH3)2N-, p-C6H5CO- and p-C6H5—N = N-groups as well as for β-naphthyl- and pyridyl(4)-rings. The applicability of a similar Hammett equation for the o-substituted compounds is not possible.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 322 (1980), S. 237-246 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of trans-4-Diphenylphosphinyl StilbenesThe reaction of 4-tolyl-diphenylphosphine oxide with N-bromosuccinimide results in 4-diphenylphosphinyl benzylbromide 5 which can be easily converted to (4-diphenylphosphinyl)-benzyl triphenylphosphonium bromide 6 and (4-diphenylphosphinyl)-benzyl diphenylphosphine oxide 7, respectively. In the presence of strong bases 6 and 7 react with aromatic aldehydes 8 to the 4-diphenylphosphinyl substituted stilbenes 1. The yields depend on the nature of base and solvent. The trans configuration of 1 is determined by i.r. and 1H-n.m.r. measurements.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 323 (1981), S. 747-754 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Protected Aminooxazolines of Arabinose and RiboseThe reaction of D-arabinose or D-ribose with cyanamide afforded 2-amino-1,2-oxazolines 1 which were treated with dihydropyran or ethylvinylether. In the presence of PTS the 3′,5′-di-THP- or 3′,5′-di-O-ethoxyethyl-D-arabino-(ribo)-furo-[1′,2′:4,5]-2-oxazolines 2 and 3 could be isolated as useful intermediates for the preparation of nucleosides.When the 2-aminooxazolines are treated with benzyloxycarbonylchloride or its p-substituted derivatives the N-3 atom of the oxazoline ring is preferentially substituted. Under these conditions the exocyclic amino function is always replaced and 2-oxo-3-benzyloxycarbonylderivatives 4 are obtained; only traces of the corresponding 2-aminoderivatives 5 are formed. Treatment of 4 with acetic anhydride, benzoylchloride, and benzoylcyanide, respectively, results in the 3′-, 5′-di-O-acyl derivatives 6. Mild hydrolysis of the benzyloxycarbonyl group with trifluoroacetic acid yields the 3′,5′-di-O-acyl-D-arabino-(ribo)-furo-[1′,2′:4,5]-2-oxooxazolidines as further intermediates for the synthesis of nucleosides.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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