Thiol In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group. Thiols are the sulfur analogue of alcohols, and the word is a portmanteau of thion + alcohol, with the first word deriving from Greek θεῖον = 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.