Nomenclature of Thiols

Thiols[1] have the functional group consisting of a sulfur and a hydrogen SH bonded to a radical (recommendation C-511.1).

thiol mercaptan sulfhydryl

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.

nomenclatura tiol

The prefix thio– can also be used to indicate a compound in which an oxygen atom has been replaced by sulfur (recommendation C-511.2).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.
thiol nomenclature formulation mercaptan SH 2-chloro-5-nitro-penta-1,3-dithiol
  • 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.

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