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NMR studies of hydrogen bonding interactions with secondary amide and urea groups
Author(s) -
Deetz Martin J.,
Fahey Julianne E.,
Smith Bradley D.
Publication year - 2001
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.391
Subject(s) - chemistry , hydrogen bond , amide , conformational isomerism , intermolecular force , chloroform , proton nmr , solvent , low barrier hydrogen bond , nuclear magnetic resonance spectroscopy , crystallography , stereochemistry , computational chemistry , molecule , organic chemistry
The cis/trans ratios for six model secondary amides were determined by 1 H NMR in a range of solvent systems. The trans to cis equilibrium in chloroform is only slightly affected by addition of the hydrogen bond donor, trifluorethanol, but the cis rotamer is stabilized by an average of 0.7 kcal mol −1 when acetic acid is used as an intermolecular donor–acceptor template. Conversely, amide interaction with anionic hydrogen bond acceptors decreases the percentage of cis rotamer. 15 N NMR spectroscopy was used to determine the effect of hydrogen bonding on the trans amide structure. The direction and the magnitude of 15 N complex‐induced‐shifts indicate that both hydrogen bond donors and acceptors raise the secondary amide rotational barrier by increasing the CN bond order. The relationship of these results to protein structure is discussed. Copyright © 2001 John Wiley & Sons, Ltd.