[Chemistry Class Notes] Nomenclature of Alkane, Alkene and Alkyne Pdf for Exam

The proliferation of organic chemistry gave rise to a number of organic compounds with broadly the same structural formula. To ensure that the nomenclature of such compounds was homogenized and was not at odds with one another, a set of rules were established by the International Union for Pure and Applied Chemistry. Thus, the nomenclature of alkanes, for instance, would differ based upon the IUPAC system. Let us look at the IUPAC names of alkane, alkene, and alkyne along with the rules for naming such compounds.

 

What is IUPAC Nomenclature?

A single chemical compound can have multiple acceptable systematic names and the systematic method that is employed for the naming of organic chemical compounds is called IUPAC Nomenclature but no two compounds can have the same name.

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

In chemistry there are several nomenclatures: apart from elements and compounds, reactions methods, pieces of apparatus, and theoretical concepts are also named leading to a very organized and systematic process.

This method of naming is known as the IUPAC nomenclature. IUPAC nomenclature of alkanes, alkynes, and alkenes are described below:

Alkanes are the simplest hydrocarbons that we know. The general formula for Alkanes is [CnH_{2n + 2}]. Alkanes only have sigma bond linkages between carbon and hydrogen. They form a series, known as the homologous series, which contain the same functional group and differ from one another by a ‘[CH_{2}]’ group.

Alkenes and alkynes are unsaturated hydrocarbons. Alkenes contain double bond linkages and in alkynes, triple bond linkages are present. 

 

Rules for the IUPAC Nomenclature of Alkanes, Alkenes, and Alkynes are Given  Below:

• Firstly the longest hydrocarbon chain is selected, which is known as the parent chain in alkanes. Therefore in the case of alkenes and alkynes, the hydrocarbon chain with the double and triple bond is chosen as the parent chain. While naming the parent chain  Greek alphabets such as hepta, octa, etc are used.

• For alkanes the suffix ‘-ane’ is used, for alkenes, the suffix ‘-ene’ is used. Similarly the suffix ‘yne’ is used for alkynes. For example, [C_{2}H_{6}] is called ethane, [C_{2}H_{4}] is called ethene and [C_{2}H_{2}] is called ethyne.

• The parent chain is numbered in such a manner that we reach the double-bonded or triple bonded carbon atom first. The position of the carbon atom having a double bond is mentioned in numerals. For example, [CH_{3}CH = CHCH_{2}CH_{3}] is named Pent-2-ene.

• If there are multiple double bonds in the carbon chain, prefixes such as di, tri are used to denote their number.