IUPAC Nomenclature of Alkanes, Alkenes and Alkynes

Earlier, most of the compounds with the same structural formula were known by different names depending on the regions where they were synthesized. This naming system was very trivial since it raised a lot of confusion. Finally, a common naming system enlisting the standard rules was set up by IUPAC (International Union for Pure and Applied Chemistry) for the naming of compounds. This method of naming is known as IUPAC naming or IUPAC nomenclature. IUPAC nomenclature of alkanes, alkynes, and alkenes are explained below:

Alkanes are the simplest hydrocarbons known to us. They have a general formula of CnH2n+2. Alkanes belong to the family of saturated hydrocarbons that is; they contain only sigma bond linkages between carbon and hydrogen. The organic compounds form a series, known as homologues series in which the successive compounds contain the same functional group and differ from one another by a ‘–CH2’ group. Alkenes and alkynes, on the other hand, are unsaturated hydrocarbons. In case of alkenes double bond linkages are seen and in alkynes, triple bond linkages are present. Rules underlying IUPAC nomenclature of alkanes, alkenes, and alkynes are discussed below:

  1. Longest hydrocarbon chain is selected and is termed as parent chain in case of alkanes. In case of alkenes and alkynes, hydrocarbon chain with double and triple bond is chosen as parent chain. Parent chain is named with the help of Greek alphabets such as hepta, octa etc.

  2. For alkanes suffix ‘-ane’ is used, for alkenes, suffix ‘-ene’ is used and suffix ‘yne’ is used for alkynes. For example, C2H6 is known as ethane, C2H4 is known as ethene and C2H2 is known as ethyne.

  3. Parent chain is numbered such that we reach to the double bonded or triple bonded carbon atom earliest. The position of the carbon atom with the double bond is mentioned in numerals. For example, CH3CH=CHCH2CH3 is named as Pent-2-ene.

  4. In case of multiple double bonds in the carbon chain, Greek numerical prefixes such as di, tri are used to denote their number.