Orbitals Distortion of Carbonyl and Olefin Groups. Unsymmetrization of π Lobes Arising from π-π Orbital Interactions

Abstract

We have detected the unsymmetrical π faces of the carbonyl groups of spiro [cyclopentane] fluorenes and 2-substituted and 3-substituted dibenzobicyclo [2.2.2] octadienones (2-substituted and 3-substituted 9, 10- dihydro-9, 10- (11-ketoethano) anthracenes) and of the olefin groups in spiro [cyclopentene]fluorenes and 2-substituted dibenzobicyclo [2.2.2] octatrienes (2-substituted-9, 10-dihydro-9, 10-ethenoanthracenes), wherein σ-type overlaps of the π orbitals are involved, in a similar manner to spiro and longicyclic conjugations, respectively. An intrinsically nonequivalent substituent at distal positions modulates the epoxidation and dihydroxylation of the olefin group and the reduction of the carbonyl group. Herein we interpret these biases or non-biases in terms of unsymmetrization of π lobes of the olefin and carbonyl π orbitals, arising from nonequivalent π-π interactions rather than from electron-donating or -withdrawing effect.