Sulfhydryl group

In organic chemistry, a thiol (/ˈθaɪɔːl/, /ˈθaɪɒl/) is an organosulfur compound that contains a carbon-bonded sulfhydryl or sulphydryl (–C–SH or R–SH) group (where R represents an alkyl or other organic substituent). Thiols are the sulfur analogue of alcohols (that is, sulfur takes the place of oxygen in the hydroxyl group of an alcohol), and the word is a portmanteau of "thion" + "alcohol," with the first word deriving from Greek θεῖον (theion) = "sulfur". The –SH functional group itself is referred to as either a thiol group or a sulfhydryl group.

Many thiols have strong odors resembling that of garlic or rotten eggs. Thiols are used as odorants to assist in the detection of natural gas (which in pure form is odorless), and the "smell of natural gas" is due to the smell of the thiol used as the odorant. Thiols are sometimes referred to as mercaptans. The term mercaptan /mərˈkæptæn/ was introduced in 1832 by William Christopher Zeise and is derived from the Latin mercurium captāns (capturing mercury) because the thiolate group bonds very strongly with mercury compounds.

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