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PPP‐VB Theory of π‐Electron Systems: Electron Delocalization, Molecular Symmetry, and Resonance
Author(s) -
Paldus Josef,
Li Xiangzhu
Publication year - 1991
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.199100040
Subject(s) - chemistry , delocalized electron , valence bond theory , antiaromaticity , electron , resonance (particle physics) , atomic orbital , covalent bond , molecular orbital theory , generalized valence bond , valence (chemistry) , molecular orbital , pentalene , molecular physics , wave function , modern valence bond theory , atomic physics , quantum mechanics , aromaticity , molecule , physics , organic chemistry
Relying on a semiempirical Pariser‐Parr‐Pople (PPP) model, it is shown that classical valence bond (VB) theory, using only a few covalent structures, can provide highly correlated energies and wave functions and thus a useful description of a molecular electronic structure, assuming that it is based on appropriate overlap‐enhanced atomic orbitals. Approximating the σ‐energy contribution by a quasi‐harmonic empirical potential, this model provides a faithful yet simple and transparent explanation of the interplay between electron derealization or resonance effects and the π‐electron localization tendency leading to bond length alternation in various π‐electron systems possessing aromatic, nonaromatic, or antiaromatic characters.