Carbon-13 NMR in liquid crystals with the removal of proton-proton dipolar couplings

Abstract

The carbon-13 spectra of liquid crystals can be simplified by applying a suitable pulse sequence to remove proton-proton dipolar couplings. The spectrum of benzene in a liquid-crystal solution becomes essentially first order. CH splittings up to four bonds can be clearly identified and dipolar coupling constants can be readily obtained without computer analysis. The one-bond coupling constant is accurate to 0.2% and the two-bond coupling constant is accurate to 2%. The three-bond and four-bond coupling constants have larger errors because of smaller splittings and overlapping of peaks.