Trigonal pyramidal carbon geometry as model for electrophilic addition–substitution and elimination reactions and its significance in enzymatic processes

Abstract

AbstractVarious examples are given in which compounds are characterized as products or intermediates in a (distorted) trigonal pyramidal (TP) geometry. These observations have taken place mainly in the field of carbocation chemistry. Special attention is given to carbenium ions formed by halogen addition to 1,1‐diarylsubstituted ethylenes focused on the electronic effects of the C‐halogen bond as axial bond in a TP geometry with regard to the π‐distribution in the rest of the molecular system. The experimental verification is accompanied by quantum chemical calculations. We also used the TP structure as a reactive model for specific enzymatic reactions. The relevance of this geometry is shown for the dehalogenation reaction of the nucleophilic displacement in dichloroethane catalyzed by haloalkane dehalogenase and for the decarboxylation of L‐ornithine with ornithine decarboxylase under loss of carbon dioxide. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007