Novel method of estimating proton–proton dipolar couplings to aid the analyses of NMR spectra of oriented molecules using two-dimensional inverse experiment

NMR spectroscopy of molecules oriented in liquid crystalline matrices provides information on the molecular structure and order parameters. Analyses of such spectra are generally carried out by numerical iterative calculations. The iterative analysis requires an initial estimate of proton–proton dipolar couplings. In the present study it is shown, for an AA′MM′X spin system, the two-dimensional HMQC experiment provides the magnitude of proton–proton dipolar couplings. In the case of an AA′A″A‴X spin system the experiment provides the initial starting dipolar couplings values for the iterative analysis. The use of this experiment in combination with two-dimensional HSQC experiments has been demonstrated for the analyses of 1,1-difluoro-1,2-dibromoethane and p-dibromobenzene.