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Bond length alternation in cyclic polyenes. VII. Valence bond theory approach
Author(s) -
Li Xiangzhu,
Paldus Josef
Publication year - 1996
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1996)60:1<513::aid-qua50>3.0.co;2-8
Subject(s) - valence bond theory , modern valence bond theory , chemistry , bond order , bond length , alternation (linguistics) , hamiltonian (control theory) , conjugated system , single bond , generalized valence bond , valence (chemistry) , atomic orbital , computational chemistry , molecular orbital , molecular physics , crystallography , electron , molecule , physics , quantum mechanics , crystal structure , mathematics , polymer , organic chemistry , group (periodic table) , linguistics , philosophy , mathematical optimization
The problem of bond length alternation in linear extended ϕ‐electron systems with conjugated double bonds is examined using the valence bond theory applied to a simple model of cyclic polyenes C N H N with N = 4 v and N = 4 v + 2 sites as described by the Pariser‐Parr‐Pople Hamiltonian. Overlap enhanced atomic orbitals are employed in order to achieve the optimal treatment with only two Kekulé structures. The predicted bond length alternation and its magnitude are in good agreement with earlier molecular orbital based calculations and with experiment. Special attention is given to the discussion of the origin of bond length alternation in long polyenic chains and to the role of the resonance energy leading to stabilization of undistorted, symmetric structures for small aromatic ( N = 4 v + 2) cycles. © 1996 John Wiley & Sons, Inc.