A dipole moment study of the ortho-effects of methyl and trifluoromethyl groups

Abstract

Apparent dipole moments in benzene of the methyl esters of 2-methyl-, 2,6-dimethyl-, 2-trifluoromethyl-, and 2,6-bistrifluoromethyl-benzoic acid have been determined. The moments of the 2-substituted esters are explained by disturbance of the conjugation between the ester and phenyl groups (i) by the electronic effects of the ortho-groups and (ii) by a twisting of the ester group out of the plane of the benzene ring. The moments of the 2,6-disubstituted esters are independent of the angular displacement of the ester group and the important contribution of Ione-pair repulsions between the substituents in methyl 2,6-bistrifluoromethylbenzoate to the dipole moment is established.