Dipole moments of some substituted acetophenones: influence of ortho substitutents on the position of the acetyl group

Abstract

The electric dipole moments of a number of substituted acetophenones, with at least one substituent (methyl, halo, nitro or amino) in the ortho position, have been measured in benzene solution and compared with the values calculated for free rotation as well as for s-trans and s-cis orientations of the acetyl group. 2-Methylacetophenones have a greater proportion of the s-cis isomer while 2-haloacetophenones have a greater proportion of the s-trans isomer. With increase in temperature there is an increase in the proportion of the less stable isomer. The observed dipole moment of O-aminoacetophenone indicates that the molecule exists predominantly in the s-cis configuration stabilized by intramolecular hydrogen bonding.