Nomenclature of Thiols

Written by J.A Dobado | Last Updated on April 22, 2024

Thiols[1] 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.[1] 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The prefix thio– can also be used to indicate a compound in which an oxygen atom has been replaced by sulfur (recommendation C-511.2).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

[1] The alternative of naming thiols as the radical to which it is attached terminated in mercaptan is discouraged by IUPAC.

Return to the page naming mono-functional compounds.

Video about the Nomenclature of Thiols