A Low-temperature Infrared Study of Self-association in Thiolic Acids

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Abstract
The i.r. spectra of thioloacetic and thiolobenzoic acids were measured in both the fundamental and first overtone regions of the S—H stretching vibration, in a mixture of CCl3F and C2F4Br2, at temperatures ranging from 20 to −190 °C. [Formula: see text] type bonds are formed at low temperatures or at high concentrations of solute. Two different species can be detected. The first is probably an open dimer and the second a cyclic dimer. The S—H anharmonicity constants are of the order of 50–60 cm−1, for both free and associated species, and have about the same value as in aliphatic or aromatic mercaptans. Carbonyl groups have lower anharmonicities. Their value is about 10 cm−1, for both free and associated species.

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