Ab initio study of the hydroxyl rotational potentials in ethanol, gauche-1-propanol and gauche,gauche-2-methyl-1-propanol

Abstract

The internal hydroxyl rotational potentials in ethanol, gauche-1-propanol and gauche,gauche-2-methyl-1-propanol have been studied with ab initio methods using 6-311G ∗∗, 6-31G ∗ and 6-31G ∗ basis sets, respectively. At the Hartree-Fock (HF) level a trans orientation of the OH group represents the global minimum for all three molecules, but when electron correlation is included in the calculations at the MP2 level, a gauche form is the most stable rotamer. The gauche minima in ethanol occur for C-C-O-H torsion angles ± 62.4°. These are shifted to ±73.4° in 2-methyl-1-propanol and to +65.3° and −72.9° in 1-propanol. The variation of bond lengths and bond angles throughout the rotations have been monitored.