A comprehensive discussion of HMBC pulse sequences. 2. Some useful variants

Abstract

AbstractThe classical HMBC experiment, introduced in the first part, has revolutionized NMR spectroscopy for the structural studies of small to medium molecules, and impressive examples for structure elucidation of organic molecules, peptides, or natural products making use of the HMBC experiment have been published in the last 20 years. In the first article, we have explored the mechanisms of the two (2D)‐HMBC pulse sequence and have discussed how the pulse sequence elements cooperate to the observed cross‐peaks, wanted and unwanted. We have seen that further improvement of the 2D‐HMBC pulse sequence can be achieved by properly setting the acquisition and processing parameters. After a short introduction, this second article, with the aid of product operator formalism, will provide a comprehensive description of some useful HMBC pulse sequences. Building from basic principles, the constant‐time HMBC variant, the sensitivity‐enhanced HMBC, and some strategy for rejecting unwanted 1 JCH signals are explained in detail. © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part A 40A: 146–169, 2012.