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NMR spin-spin couplings involving nuclei in the neighborhood of a carbonyl group. 3JCH couplings in α-substituted acetamides

✍ Scribed by Susimaire Pedersoli; Francisco P. dos Santos; Roberto Rittner; Rubén H. Contreras; Cláudio F. Tormena

Publisher: John Wiley and Sons
Year: 2008
Tongue: English
Weight: 105 KB
Volume: 46
Category: Article
ISSN: 0749-1581
DOI: 10.1002/mrc.2158

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✦ Synopsis

Abstract

In this work ^3^J~CH~ spin‐spin coupling constants (SSCCs) for the cis‐ and __trans‐__conformers for α‐X‐acetamides (X = F, Cl, Br and CN) (1–4) were studied in detail since they were found to be notably different for both conformers. These differences are rationalized as originating in the changes of the strong negative hyperconjugative interactions that take place within the carbonyl group. Such changes are found to depend not only on conformation, but also on solvent. For the cis‐conformers there is a close proximity between the X‐substituent and the in‐plane oxygen lone pair of pure p character, which affects notably their respective negative hyperconjugative interactions. Both the efficiency for transmitting the Fermi contact (FC) term through the coupling pathway of ^3^J~CH~ SSCCs and its potential as a probe to study the stereochemical properties of the XH~2~C group are discussed. Copyright © 2008 John Wiley & Sons, Ltd.

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