Chapter 2 - Methodology and Applications of Heteronuclear and Multidimensional 13 C NMR to the Elucidation of Molecular Structure and Dynamics in the Liquid State

Abstract

This chapter deals with modern multidimensional NMR techniques involving 13C nuclei. Their significance for structure elucidation sensitivity and resolution are two main aspects, which are connected to direct or inverse detection. The type of detection used affects the requirements on the sample, i.e., whether a naturally abundant substrate can be used or if isotopic enrichment is necessary instead. Another important issue is the determination of homo- and heteronuclear coupling constants. The chapter discusses the basic heteronuclear coherence transfer steps: INEPT, DEPT, and heteronuclear Hartmann–Hahn. The important multidimensional NMR techniques involving 13C, either for unlabeled or 13C-enriched molecules, are heteronuclear single-quantum (HSQC) and multiple-quantum coherence (HMQC). The chapter describes the meaning of heteronuclear scalar couplings for structural studies and some NMR techniques for their experimental determination. The measurement of 13C relaxation times and their implications for the molecular structure are also explained. The techniques and the estimated values for typical sample concentrations and measuring times vary considerably from case to case, since they depend on a few sample-specific factors such as relaxation behavior, solubility, and spectral dispersion. However, this data is useful in estimating relative sensitivities of the different NMR techniques.