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 provi des information on the molecular structure and order parameters. Analyses o f such spectra are generally carried out by numerical iterative calculation s. The iterative analysis requires an initial estimate of proton-proton dip olar couplings. In the present study it is shown, for an AA ' MM 'X spin sy stem, 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-dime nsional HSQC experiments has been demonstrated for the analyses of l,1-difl uoro-1,2-dibromoethane and p-dibromobenzene. (C) 2001 Elsevier Science B.V. All rights reserved.