Intramolecular Hydrogen Bonding of ortho-Substituted Benzenethiols

From the infrared, NMR, and dipole moment measurements on several substituted benzenethiols, the intramolecular hydrogen bonding in o-halo, o-methoxy, o-nitro, and o-carbomethoxybenzenethiols is verified. Fivemembered S–H···X hydrogen bonds cause remarkable enhancements of their S–H stretching absorptions without considerable frequency shifts. The favorable s-cis conformations in these thiols are also proved by comparing their experimental dipole moments with theoretical values. By far stronger hydrogen bond is observed in o-carbomethoxybenzenethiols which can form six-membered chelate ring by the intramolecular hydrogen bonding.