Current aspects of practical two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy: applications to structure elucidation.

The intense effort in developing new 2D NMR methodology over the past decade has been driven by the desire to study molecules of progressively greater complexity. The need for refined structural detail has produced new types of experiments that require more involvement on the part of the practicing spectroscopist in understanding the theoretical bases leading to their experimental realization. In this Review we discuss several concepts that are important in the successful application of current versions of the most useful 2D NMR experiments, such as coherence transfer, phase cycling, apodization functions, and obtaining pure-phase 2D NMR spectra. The intimate interconnections among these concepts are emphasized. The principles underlying the 2D NMR experiments are described and then the experiments are illustrated in assigning the 1H and 13C NMR spectra of the triterpene, ursolic acid.