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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio MO study of benzylic cations - 2. Steric effects on the resonance interaction and on the resonance demand in the Yukawa-Tsuno equation (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 573-582 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Geometries of secondary and tertiary benzylic cations, which have bulky substituents at α positions, were optimized by ab initio MO calculations at the RHF/6-31G* and, in part, MP2/6-31G* levels. Calculated øcalc, which is the dihedral angle of the α-C (SINGLE BOND) C bond with respect to the aromatic plane, is compared with the relative resonance demand r/rmax obtained from solvolysis reactivity and also cation stability; r and rmax are the resonance demand in the Yukawa(SINGLE BOND)Tsuno equation for any given system examined and the corresponding ideal full-resonance stabilized demand, respectively. The results suggest that there is a close relationship between the experimental and calculated relative resonance demands expressed by r/rmax = cos2 øcalc, which is suggested by HMO theory for the resonance interaction in the benzyl cation. Thus the r value is a good parameter indicating the degree of resonance interaction between benzylic 2p π-orbital and the benzene π-system.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio MO study of benzylic cations. Part 3. Protonated benzoyl derivatives (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 857-870 
    Details
    ISSN: 0894-3230
    Keywords: Yukawa-Tsuno equation ; substituent effect ; α-hydroxybenzylic cation ; benzoyl compound ; ab initio calculation ; basicity ; proton affinity ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Structures of α-hydroxybenzylic cations and their conjugate bases, which cover a wide variation of stability, were optimized by means of ab initio molecular orbital method at the RHF/6-31G* level. Total energies were calculated at the MP2/6-31G*//RHF/6-31G* + ZPE (scaled 0.9) level. Calculated relative proton affinities of the respective neutral molecules (benzoyl compounds; conjugate bases of α-hydroxybenzylic cations) agreed well with the corresponding basicities in the gas phase. The geometries of α-amino-α-hydroxybenzyl and α-hydroxy-α-dimethylaminobenzyl cations were also optimized at the fixed dihedral angles between the cationic 2pπ orbital and the benzene π orbital (φ), and between the cationic 2pπ orbital and lone pair electron orbital of the α-substituent (θ). The changes in Wiberg bond orders and the rotational potentials about φ and θ showed that the degree of resonance interaction between the cationic center and phenyl ring is balanced by the electronic effects of α-substituents in benzylic cations. The obtained theoretical indices of all parent cations such as Mulliken population, Wiberg bond order and bond lengths were correlated linearly with the resonance demand parameter (r value) which were given by the Yukawa-Tsuno substituent effect analysis in the gas phase and in aqueous solution. These relationships are consistent with those for other benzylic cations such as destabilized carbocations and sterically hindered cations studied previously. This confirms that the empirical r value has a definitive physical meaning, i.e. a measure of the resonance interaction between the cationic center and the aryl moiety. Copyright © 1998 John Wiley & Sons, Ltd.
    Additional Material: 12 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio MO study of benzylic cations - 1. Some theoretical parameters related to the resonance demand in the Yukawa-Tsuno equation (1996)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 9 (1996), S. 561-572 
    Details
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Structures of 14 kinds of benzylic cations into which are introduced various substituents at benzylic position were optimized by means of the ab initio molecular orbital method at the RHF/6-31G* level. The theoretical indices obtained associated with the resonance interaction, such as population, bond order and bond length, were compared with the resonance demand parameter (r value) of corresponding solvolysis systems that were given by the Yukawa-Tsuno substituent effect analysis. The r value was linearly correlated with the theoretical resonance indices.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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