A comprehensive discussion of hmbc pulse sequences, part 1: The classical HMBC

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Abstract
Since its introduction in 1986, the heteronuclear multiple bond correlation (HMBC) experiment has modernized nuclear magnetic resonance spectroscopy for the structural studies of small to medium molecules. The experiment provides information about which protons are near through bonds (but not directly bonded to) different carbons or to another heteronucleus. This experiment (in conjunction with the heteronuclear single‐quantum coherence experiment) provides significant amount of information about molecular structure, as the long‐range proton–carbon or proton–nitrogen correlations can include quaternary carbons or nitrogens, in addition to protonated carbons or nitrogens. Impressive examples for structure elucidation of organic molecules, peptides, or natural products have been published in the last 20 years. After a short introduction into the basic theory, this article will provide a comprehensive and pedagogical description of the classical HMBC pulse sequences, with the aid of product operator formalism. Building from basic principles, low‐pass filtering for rejecting unwanted 1 JCH correlations, and the role of pulsed‐field gradients for coherence transfer pathway selection are explained in detail. This article is intended to be used as a basic coverage for students and researchers seeking a simple theoretical understanding of the fundamental tools of the HMBC experiment. © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part A 40A: 101–127, 2012.

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