Review lecture: Nuclear magnetic resonance spectroscopy in two frequency dimensions

Abstract

Abstract A spectrum is normally thought of in terms of a graph of absorption intensity as a function of frequency, and in this form it has served us well for many years. A recent development extends this idea into a second frequency dimension, the spectrum now being represented by a surface in three-dimensional space. The examples are in the field of high resolution nuclear magnetic resonance (n.m.r.) spectroscopy, although the principle is rather more general, being based on the two-dimensional Fourier transformation of a transient response that is a function of two independent time variables t1 and t2. By arranging for different experimental conditions to prevail during t1 and t2, it is possible to separate different n.m.r. parameters, for example chemical shifts and spin coupling constants, into the two frequency dimensions. There is also an important element of correlation involved, since during t2 the nuclei ‘remember’ their past history during t1,and this has been used to correlate proton and carbon-13 chemical shifts.