Chapter 13 - Elucidation of Molecular Structure and Macromolecular Conformation

Abstract

High-resolution nuclear magnetic resonance (NMR) is used mainly as a valuable tool in the elucidation of molecular structure, as a quantitative analytical technique, and as a means for understanding molecular reactions. This chapter provides an overview of the approach to structure elucidation problems and gives a few examples to indicate the scope of these important applications. In problems of structure elucidation, an NMR spectrum may provide useful, even vital data; knowledge of the source of the compound or its method of synthesis is frequently the single most important fact. Additionally, the interpretation of the NMR spectrum is carried out with concurrent knowledge of other physical properties, such as elemental analysis from combustion or mass spectral studies, the molecular weight, and the presence or absence of structural features, as indicated by infrared or ultraviolet spectra or by chemical tests. Two-dimensional NMR provides powerful techniques to aid interpretation, but the starting point is a simple, one-dimensional proton NMR spectrum, with careful integration to ascertain the relative numbers of protons in different lines or multiplets. In some instances, one or two good 1H NMR spectra may be sufficient to solve the problem with little expenditure of instrument time.