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NMR spin‐spin couplings involving nuclei in the neighborhood of a carbonyl group. 3 J CH couplings in α‐substituted acetamides
Author(s) -
Pedersoli Susimaire,
dos Santos Francisco P.,
Rittner Roberto,
Contreras Rubén H.,
Tormena Cláudio F.
Publication year - 2008
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2158
Subject(s) - chemistry , conformational isomerism , substituent , lone pair , spin (aerodynamics) , coupling constant , group (periodic table) , crystallography , stereochemistry , computational chemistry , molecule , organic chemistry , physics , engineering , particle physics , aerospace engineering
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.