Thiols have the functional group consisting of a sulfur and a hydrogen SH bonded to a radical (recommendation C-511.1).
Where R represents an alkyl group or other organic substituent.
Thiols have traditionally been called mercaptans. They are named analogously to the IUPAC form of alcohols (-OH), the -SH group is also called sulfhydryl. For example, the compound CH3SH would be methanethiol, and CH3CH2SH is called ethanethiol.
The prefix thio– can also be used to indicate a compound in which an oxygen atom has been replaced by sulfur (recommendation C-511.2).
Steps for name assignment
- The chain that is the longest and contains the -SH is chosen as the main chain.
- We number such a chain so that the carbon attached to -SH has the lowest possible numbers.
- The main chain is named by specifying the number of carbon atoms in that chain with a prefix (ethane– two carbons, propane– three carbons, butane– four carbons; ...etc).
- The -SH are identified with their respective numbers separated by commas.
- The termination is placed indicating the number of -SH (-thiol one SH; –dithiol two SH; –trithiol three SH; … etc.).
- The -SH group has priority over double bonds, nitro groups and halogens.
References and notes
 The alternative of naming thiols as the radical to which it is attached terminated in mercaptan is discouraged by IUPAC.