Two-Dimensional (2D) NMR Methods

1 Basics of Two-dimensional NMR

Malcolm H. Levitt

Department of Chemistry, University of Southampton, SO17 1BJ, Southampton, UK

1.1 Introduction

1.1.1 Time-domain NMR

The introduction of pulse-Fourier transform (pulse-FT) NMR in 1966 by Ernst and Anderson [1] represented a paradigm shift, not only in nuclear magnetic resonance but also in many other forms of spectroscopy. Prior to this seminal experiment, there were two forms of NMR, which were generally viewed as being quite distinct and practiced mainly by chemists on the one hand, and physicists on the other.

Chemical applications of NMR spectroscopy used a “continuous-wave” (cw) method, in which chemical shifts and spin-spin couplings were probed, either by (i) varying the frequency of applied radiofrequency irradiation and detecting a change in the nuclear magnetic response when the applied frequency matches a nuclear energy level spacing, or (ii) by applying radiofrequency irradiation of fixed frequency and varying the applied magnetic field while monitoring the response. For technical reasons, the latter method (fixed frequency, variable field) was easier to perform and more common. A residue of this historical method still persists in the common nomenclature of modern NMR, where the terms “high field” and “low field” are still often used (despite a jarring logical inconsistency) to characterize nuclei in electron environments, which are relatively weakly shielded from the external magnetic field (low field!), and for ...