On the nature of molecular conformations inferred from high-resolution NMR.

The basic, usually unstated, premises underlying the derivation of "average" conformations of flexible molecules from high-resolution NMR parameters (shifts, coupling constants and relaxation times) are critically examined. It is shown that in cases where the individual conformers contributing to the average are not known the "average" derived from spectroscopic data represents a virtual structure devoid of physical meaning.