Intramolecular OH···S hydroen bonds and molecular conformations in 2-methylmercaptoethanol

Abstract

The infrared absorption spectrum of monomeric 2-methylmercaptoethanol in dilute CC1₄, solution exhibits four overlapped bands in the fundamental OH stretching region. The individual band components were resolved using digital computing techniques [1], and the relative band intensities are temperature dependent. The "free" OH bands at 3634 and 3623 cm correspond to gauche and trans orientations about the C-O bond, respectively, by analogy with similar band components in the infrared spectrum of ethanol in dilute CC1₄, solution. The OH bands at 3539 and 3446 cm^-1 are assigned to gGt and gGg¹ conformers, respectively, each involving an intramolecular OH···S hydrogen bond (conformer notation refers to the orientation about the C-O, C-C and C-S(CH₃) bonds, respectively). A similar interpretation of the matrix isolated infrared spectra of ethylene glycol, involving two conformers with intramolecular OH···O hydrogen bonds and differing principally in the orientation of the proton-acceptor OH group, has been presented recently [2]. The microwave spectrum of 2-mercaptoethanol in the vapour phase arises from an all-gauche conformation with an intramolecular OH···S hydrogen bond [3].