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A theoretical and experimental 1 H NMR spectroscopy study of the stereoelectronic interactions that rule the conformational energies of alanine and valine methyl ester
Author(s) -
Cormanich Rodrigo A.,
Ducati Lucas C.,
Tormena Cláudio F.,
Rittner Roberto
Publication year - 2013
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.3180
Subject(s) - chemistry , steric effects , hyperconjugation , intramolecular force , alanine , nuclear magnetic resonance spectroscopy , hydrogen bond , computational chemistry , stereochemistry , valine , amino acid , molecule , organic chemistry , biochemistry
Amino acids exhibit a bipolar zwitterionic structure ( + H 3 N‐CHR‐COO − ) in solution; hence, conformational studies of these compounds have been limited to the gas phase. The conformational preferences of amino acids have been widely attributed to intramolecular hydrogen bonding, despite steric and hyperconjugative effects. In this work, we propose the conformational study of alanine and valine methyl esters, which do not show zwitterionic structures in solution, by 1 H NMR and theoretical calculations. The 3 J HH spin–spin coupling constants and theoretical calculations were found to be in agreement, showing that the interplay between steric hindrance and hyperconjugation is the forces that are responsible for determining the conformational preferences of alanine and valine methyl esters. Copyright © 2013 John Wiley & Sons, Ltd.