Thiol with a blue-highlighted sulfhydryl group. In organic chemistry, a thiol (/ˈθaɪˌɔːl/ , /ˈθaɪˌɒl/) is an organosulfur compound that contains a carbon-bonded sulfhydryl (–C–SH or R–SH) group (where R represents an alkane, alkene, or other carbon-containing group of atoms).