Angular-group-induced bond alternation. I. Origin of the effect from Ab Initio calculations

Abstract

It is shown that an angular group -XY attached to the benzene ring causes bond length alternation within the ring. This angular-group-induced bond alternation (AGIBA) effect is studied in several mono-substituted benzene derivatives by means of the ab initio calculations. Different alternation patterns are found for angular groups of the -X-Y and -X=Y types. The origin of the AGIBA effect is traced to a competing influence of through-space-π-electron interactions and a rehybridization effect at the substituted carbon atom. The AGIBA effect is shown to be strongly conformation dependent.