Dipole moments and conformation of peroxy esters

Abstract

Dipole moments of sixteen substituted peroxybenzoic esters III, IV were measured in benzene solution and interpreted in terms of the conformation around the O-O bond. The dipole moment of the CO3R group is different for R = methyl and R = tert-butyl, viz. 9.0 and 10.4 . 10-30 C m, respectively. Its solution into components was carried out making reference to the dipole moments of substituted benzoic esters as model compounds. As a result the dihedral angle τ = C-O-O-C was estimated to 160-180° in the case of tert-butyl peroxy esters IV and to 110-150° in the case of methyl peroxy esters III. The mesomeric dipole moment expressing the conjugation within the ester group was estimated to 0.8 or 1.5 . 10-30 C m for methyl or tert-butyl esters, respectively.