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.