CHAPTER 14 - Modern Spectroscopic Approaches to Structure Elucidation

Abstract

This chapter discusses the modern spectroscopic approaches to structure elucidation. The establishment of the molecular formula is critical in the structure determination process of natural products. High-resolution electron-impact mass spectrometry has usually provided such unequivocal determinations. Soft ionization techniques such as high-resolution fast-atom bombardment mass spectrometry methods have considerably extended the applications of high-resolution mass spectrometry to higher molecular weight ranges, particularly of nonvolatile, polar compounds. Depending on the particular instrumentation available, the accuracy of these methods does not always define an empirical formula uniquely but provides a range of formulas especially in the molecular weight range above 500. It is in the realm of long-range 1 H– 13 C connectivities that the most dramatic achievements have been realized. The combination of restricted ambiguity and dramatic improvements in sensitivity has projected this methodology into the forefront of modern structural analysis.