Intramolecular Hydrogen Bonds. XVII. Intramolecular Hydrogen Bonding Involving the Mercapto Group as a Hydrogen Donor

The SH stretching absorption spectra of some mercapto compounds in dilute carbon tetrachloride solutions and also in acetonitrile solutions have been measured at 20°C. Alkyl mercaptans show absorption bands which are suggestive of the rotational isomerism around the C–S bond. The spectral data indicate that benzyl mercaptan, ω-ethoxyalkyl mercaptans, and ethyl α- and β-mercaptoalkanoates form practically no intramolecular hydrogen bond between the SH group and the hydrogen-acceptor group. In thiosalicylic acid and its ethyl ester, the hydrogen-bonding to the carbonyl group is partially possible even in acetonitrile. On the other hand, the corresponding free carboxylic acids are not hydrogen-bonded between the S atom and the carboxyl group.