A theoretical and experimental 1H NMR spectroscopy study of the stereoelectronic interactions that rule the conformational energies of alanine and valine methyl ester

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Amino acids exhibit a bipolar zwitterionic structure (+H3N-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, by1H NMR and theoretical calculations. The 3JHH 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 (c) 2013 John Wiley & Sons, Ltd.2610849857Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq