Molecular Conformations of γ-Aminobutyric Acid and γ-Amino-β-hydroxybutyric Acid in Aqueous Solution

Proton magnetic resonance and Raman spectra indicate that the backbone of γ-aminobutyric acid is fairly flexible and rotational isomers are almost equally populated in aqueous solution. The population is not much affected by change of pH. On the other hand, in γ-amino-β-Hydroxybutyric acid the trans-trans and gauche-trans conformations of the backbone are equally populated in neutral solution, trans-trans conformation being predominant in non-zwitterionic forms. The conformation in solution is discussed in relation to the structure of these molecules in crystal.