Multiple quantum NMR study of correlation of two methyl groups

Molecules which have rotating groups may show coupled motions. As an example, two adjacent methyl groups may exhibit some degree of correlated motion as two wheels in gear. 1 The spectra obtained by traditional single quantum NMR in oriented molecules may sometimes be complicated and difficult to analyze. However, the techniques of multiple quantum (MQ) NMR spectroscopy can yield analyzable spectra26 and have been used to study conformation 1 and correlated relaxation. 8-11 In this Communication, we would like to report the first preliminary and illustrative results on the study of correlation of two methyl groups by multiple quantum (MQ) NMR. We show that the high n-quantum spectra distinguish simp ly between the cases of uncorrelated motion (independent rotation) and correlated motion (geared rotation). As an example we present results on the system to partially oriented 2, 3-dimethylmaleic anhydride oriented in a liquid crystal solvent.