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Effect of halogen substitution on p‐ phenylenebiscarbene
Author(s) -
Nicolaides Athanassios
Publication year - 2005
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/qua.20619
Subject(s) - diradical , halogen , chemistry , singlet state , wave function , degenerate energy levels , valence (chemistry) , triplet state , computational chemistry , valence bond theory , ground state , fluorine , perturbation theory (quantum mechanics) , atomic physics , molecule , quantum mechanics , physics , excited state , molecular orbital , organic chemistry , alkyl
Abstract The effect of halogen (F, Cl, and Br) perturbation on the geometries and relative energies of five electronic states (one quintet, two triplets, and two singlets) of p ‐phenylenebiscarbene (1‐H) was examined computationally using MCSCF/6‐31G(d) wavefunctions. In all four cases (1‐X, X=H, F, Cl, Br) the ground state is a singlet diradical of A′ symmetry. Halogen substitution is found to have a minimal effect on the geometries and on the relative energies of electronic states of the same symmetry. However, it has a pronounced stabilizing effect on the energies of the A″ states relative to the A′ ones. Among the halogens the stabilization is strongest for the fluorine derivative resulting in a small T(A″)‐S(A′) splitting of 8 kcal/mol. The hydroxy analog (1‐OH) has almost degenerate singlet A′ and triplet A″ states, whereas the amino‐substituted one (1‐NH 2 ) is computed to be a ground‐state (A″) triplet. Several of the findings can be accommodated by a qualitative valence‐bond model, which also relates the T(A″)‐S(A′) splittings in 1‐X and the corresponding phenylcarbene (PhCX). © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005