CONFORMATIONAL STABILIZATION BY INTRAMOLECULAR OH-CENTER-DOT-CENTER-DOT-CENTER-DOT-S AND CH-CENTER-DOT-CENTER-DOT-CENTER-DOT-O INTERACTIONSIN 2-(METHYLTHIO)ETHANOL - MATRIX-ISOLATION INFRARED-SPECTROSCOPY ANDAB-INITIO MO CALCULATIONS

The conformational stability of 2-(methylthio)ethanol has been studied by matrix-isolation infrared spectroscopy and ab initio MO calculatio ns. In an argon matrix, the conformer with gauche-gauche-gauche' (GGg' ) around the CS-C-C-OH bonds is the most stable and the G'Gg' conforme r is the second most stable. These and the TGg' conformers are stabili zed by intramolecular hydrogen bonding between the hydroxyl hydrogen a tom and the sulfur atom. The relative strength of the hydrogen bonding in these conformers is in the order GGg' > TGg' > G'Gg', as estimated from the nonbonded OH ... S distance. In the G'Gg' conformer, an addi tional intramolecular interaction between the methyl hydrogen atom and the hydroxyl oxygen atom is involved. The relative strength of this 1 ,5-CH ... O interaction in the G'Gg' conformer is the least among the three relevant conformers with G'G around the CS-C-COH bonds. The calc ulated results indicate that the geometry of this conformational form is considerably distorted so that it is simultaneously accessible to b oth of the interactions. This geometry is, however, not best suited fo r the respective interactions to be the most effective. The results fo r 2-(methylthio)ethanol have been compared with those for 2-methoxyeth anol, in which the analogous intramolecular interactions are involved. The present study emphasizes the importance of the intramolecular int eractions in the conformational stabilization of 2-(methylthio)ethanol and other relevant compounds.