Nuclear Magnetic Resonance Spectroscopy: Strategies for Structural Determination
A glance at any recent chemistry journal immediately illustrates the reliance that modern chemistry places on nuclear magnetic resonance (NMR) spectroscopy as a quick and reliable method for the elucidation of molecular structures. NMR spectroscopy has been the single most important physical method for the determination of molecular structures for more than 40 years. The power of the technique lies not only in defining the numbers and types of nuclei present in an organic molecule, but also in describing their individual chemical environments and, more importantly, the way they are interconnected. Driven by its potential to determine the structures of organic compounds, NMR spectroscopy has seen substantial development in the six decades since the first experiments. In particular, the implementation of the pulsed Fourier transform (FT) method1 and, subsequently, the concept of multidimensional experiments2 provided the seeds for vibrant growth. There are currently hundreds of multipulse experiments available to the NMR spectroscopist. However, only a small proportion of these procedures are regularly employed for the solution of molecular structures. The most useful experiments have been the subject of numerous reviews.3-15
This chapter aims at introducing NMR spectroscopy to the reader who is unfamiliar with the technique. Within the context of the multidisciplinary nature of bioactive natural product research, the chapter will briefly review the most utilized NMR experiments with the aim of highlighting the types of information that each can provide. Theoretical and experimental details of each procedure will be kept to a minimum with references to the literature for readers who require further information. Section 3.2, introduces the essential concepts. Subsequently, the most useful NMR techniques will be discussed approximately in the order that they would be applied to solve the structure of an unknown compound. Sample spectra have been chosen with the aim of clearly demonstrating each technique without the need for detailed argument.