Hydrogen bonding, tautomerism and normal vibrations of thiol acids

Hydrogen bonding in thiolformic, thiolacetic and dithioformic acids has been investigated by CNDO/2 and extended Hückel methods. In thiol acids, hydrogen bonds formed by both the hydroxy and the thiol forms are examined. Cyclic dimers of the hydroxy form are more stable, as in carboxylic acids, while the open dimers are more stable in the case of the thiol form. Dithioformic acid forms very weak hydrogen bonds compared to thiol acids. Vibrational assignments have been made for the hydroxy and thiol forms of thiolformic acid as well as for the thioformate ion based on normal vibration analysis.