The gauche effect is governed by internal hydrogen bond in 2-amino-2-methyl-propanol

Abstract

The conformational isomerism of 2-amino-2-methyl-propanol (AMP) was theoretically studied using ab initio and DFT methods, both in the gas phase and implicit solvents. A gauche structure among 13 possible conformers was highly prevalent in the vacuum, nonpolar (cyclohexane) and polar (acetonitrile) solution. Natural bond orbital analysis and the quantum theory of atoms in molecules indicate the appearance of intramolecular hydrogen bond, especially the OH…N interaction, which was found to govern the conformational isomerism and, therefore, the gauche effect in AMP for both the isolated molecule and in solution. Such an interaction has a strong hyperconjugative contribution, as well as the antiperiplanar interactions usually invoked to explain the gauche effect, namely the σCH → σ*CN and σCC → σ*CO interactions, which are stronger than the corresponding σCO → σ*CN and σCN → σ*CO interactions in the anti conformers. Intermolecular hydrogen bond takes place according to an explicit solvent (water) model. For the neat liquid, the gauche conformation is also preferred, according to infrared analysis of the C–O stretching mode, but intermolecular interactions should also be present.