Structure and Nomenclature of Thiols and Sulfides

Thiols and sulfides are sulfur equivalents of alcohols and ethers, respectively, where the sulfur atom replaces the oxygen atom of alcohols and ethers.

Thus, thiols have the –SH functional group, also known as the sulfhydryl or the mercapto group, bonded to a hydrocarbon group.

Sulfides, or thioethers, have the central sulfur atom flanked by two hydrocarbon groups on either side.

Accordingly, sulfides can be symmetrical, with two identical groups on both sides, or asymmetrical, with two different groups.

 Like alcohols and ethers, thiols and sulfides also exhibit a bent geometry, with the C–S–H  and C–S–C bond angles smaller than the corresponding C–O–H and C–O–C bond angles of alcohols and ethers.

When comparing the bond lengths, the C–S bond of thiols and sulfides is longer than the C–O bond of corresponding alcohols and ethers. Similarly, the S–H bond of thiols is longer than the O–H bond of alcohols.

Common names of thiols are derived by adding the suffix "mercaptan" to the name of the alkyl group bonded to the –SH group.

The IUPAC names for thiols use the suffix "thiol" to follow the name of the parent hydrocarbon chain without dropping the letter "e" from the parent chain's name.

The parent chain is numbered from the end close to the –SH group, with the locants indicating the position of the sulfhydryl group and substituents as prefixes.

When present as a substituent, the sulfhydryl group is prefixed as "mercapto" before the parent chain's name.

Common names of sulfides are assigned by adding the suffix "sulfide" to follow the names of alkyl groups listed alphabetically.

When deriving the IUPAC names of sulfides, the longest carbon chain is considered as the parent alkane. The smaller alkyl group containing sulfur is named an alkylthio group and prefixed to the parent alkane's name.