Conformational Analysis of 1,4-Dithiane Derivatives

Abstract

α-Mercapto ketones either exist as such (I-a; II-a; III-a) or dimerise to 2,5-dihydroxy-1,4-dithiane derivatives (I-b; II-b; III-b). The wide range of melting-points reported for these specific compounds provides a confusing dimension to the question of their structure. Infrared spectroscopy has given a qualitative evidence that these compounds exist in solution as a mixture of both forms. Cryoscopic molecular-weight measurements have also given values varying between those for one or two units. In addition to these, ¹H-nmr spectra have given good evidences that α-mercapto ketones are formed as a mixture of monomer and a dimer. No evidences are found to support the previously claimed isolation of two dimeric species. Generally, the dimer dissociates to the monomer on standing as a solution in chloroform, while the monomer is dimerised by the grinding effect.