Carbon-13 nuclear magnetic resonance of unsymmetrically ortho-disubstituted benzenes. Spectral analysis of phthalic and maleic acid monoesters

Abstract

A simple and rapid technique for the analysis of certain ¹³C n.m.r. spectra has now been demonstrated to be applicable to the spectra of unsymmetrically ortho-disubstituted benzenes. The ¹H coupled spectra of these compounds reveal characteristic differences in the splitting patterns of the protonated ring carbons. This phenomenon has been used to assign the ¹³C n.m.r. signals of a series of phthalic acid monoesters. In addition the ¹³C n.m.r. spectra of the structurally and electronically related maleic acid monoesters are assigned. The effects of phthalate or maleate monoesterification on the ¹³C chemical shifts of a series of alcohols are recorded and compared to recent accounts concerning other esters. These data reveal that ¹³C chemical shifts induced by esterification of alcohols are relatively consistent, and predictable, regardless of the group attached to the carboxy-function.