MODERN NMR PULSE EXPERIMENTS - A GRAPHICAL DESCRIPTION OF THE EVOLUTION OF SPIN SYSTEMS

Many modern methods designed to enhance the power of NMR spectroscopy have been widely adopted by the scientific community. Some of the best known among these techniques are one‐dimensional methods for polarization enhancement and spectral editing (“INEPT” and “DEPT”) and various two‐dimensional experiments such as correlation spectroscopy (“COSY”) and nuclear Overhauser spectroscopy (“NOESY”). Most of these methods cannot be described in terms of classical magnetization vectors, and although they can be understood with the help of the density operator formalism, this approach remains difficult for many users, in part because of its cumbersome notation, which prevents one from recognizing the important features at a glance. In this paper, a set of graphical conventions is described which allows one to represent the effect of sequences of radio‐frequency pulses on spin systems in a variety of experiments. The graphs provide a concise description of the network of spins that are coupled through scalar and dipolar interactions, of the state of a spin system expressed in terms of products of operators, and, most importantly, of the transformations from one state to another due to the effect of radio‐frequency pulses, chemical shifts, and scalar couplings. The graphical approach also allows one to represent the effect of phase‐cycling and multiple‐quantum filtration, cross‐relaxation (Overhauser effects) and cross‐correlated relaxation. Copyright © 1990 by VCH Verlagsgesellschaft mbH, Germany