Mercaptans

In organic chemistry, a thiol is a organosulfur compound that contains a carbon-bonded sulfhydryl (-C-SH or R-SH) group (where R represents an alkane, alkene, or other carbon-containing moiety). Thiols are the sulfur analogue of alcohols, and the word is a portmanteau of “thio” + “alcohol,” with the first word deriving from Greek θειον (“thion”) = “sulfur”. The -SH functional group itself is referred to as either a thiol group or a sulfhydryl group. Many thiols have strong odours resembling that of garlic. They are used as odourants to assist in the detection of natural gas (which in pure form is odourless), and the “smell of natural gas” is in fact due to the smell of the thiol used as the odourant.