Determination of long-range 13C-13C dipolar couplings using a 13C labeled liquid crystal

A liquid crystal labeled with a single C-13 nucleus, 4'-cyano-4-biphenyl hexanoate-1-C-13, has been synthesized for the purpose of measuring long-range C-13-C-13 dipolar coupling constants. The proton-decoupled C-13 spectrum of this compound gives eleven C-13-C-13 dipolar coupling constants for carbon nuclei ranging from one to seven bonds away from the labeled C-13 position. In addition, although H-1-C-13 dipolar coupling constants for carboxyl carbons have never been determined from the 2D technique of proton encoded local field spectroscopy using naturally abundant liquid crystals, three such coupling constants were obtained using the C-13-enriched compound 4'-cyano-4-biphenyl hexanoate-1-C-13.