In organic chemistry, a thiol (, ) 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). 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 ("thion") = "sulfur." The –SH functional group itself is referred to as either a thiol group or a sulfhydryl group.