Chapter 1 - Introduction

Abstract

This chapter reviews the technique of nuclear magnetic resonance (NMR), which has become a powerful spectroscopic and imaging tool applied in different areas, from materials science to chemistry, molecular biology, and medicine. The first publications on 13C NMR spectroscopy were presented in 1957. Two major developments contributed significantly to the establishment of 13C NMR as a routine technique: the Fourier transform (FT) approach and broadband proton decoupling. By using proton-enhanced NMR, signals of dilute nuclei were enhanced by repeatedly transferring polarization from a more abundant species to which they were coupled. High resolution was attained through decoupling of the abundant spins, usually protons. Cross-polarization for enhancing the signals of low-sensitivity nuclei in solids was extended to measurements in the liquid state. Heteronuclear polarization transfer techniques have played a central role in 13C NMR. Three approaches are explored in the chapter: enhancement of the initial 13C polarization, indirect detection of the 13C resonances by looking at proton signals, and editing of spectra by selecting resonances belonging to specific subunits in a spin system, such as the CH, CH2, and CH3 groups.