Conformational analysis of alkoxyalcohols A combined IR and molecular mechanics study

Abstract

The conformational behaviour of one branched and three linear alkoxyalcohols has been investigated by IR spectroscopy and molecular mechanics (MM). The OH-stretching region (3750–3150 cm^-1) has been studied in dilute apolar solution. In the MM calculations, for each compound all unique staggered conformations have been analysed, both with and without contributions to the steric energy from rotational and vibrational energy and entropy. The corrections enhance the amount of non-bonded conformers and significantly improve the agreement between theoretical and experimental populations. Calculated H-bond geometries are seen to be related with observed OH-stretching vibrations. The agreement between theoretical and experimental frequency shifts (Δ_OH, i.e. the difference between free and bonded) is poor, especially for short H-bond contacts, thus making calculated OH-stretching frequencies unsuitable for assignment purposes.