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3.3: Nomenclature of Alkanes

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Organic Chemistry

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Nomenclature of Alkanes

3.3: Nomenclature of Alkanes

In the late 19th-century, the number of new chemical compounds discovered increased tremendously. Hence, the necessity arose to develop a naming system for the systematic nomenclature of these newly discovered compounds. IUPAC (International Union for Pure and Applied Chemistry), established in 1919, sets rules for the nomenclature.

The alkane nomenclature considers the length of the carbon chain, the number, and the location of the substituent to arrive at its systematic name. The IUPAC nomenclature is done stepwise, and it is universally acceptable. The first step is to determine and name the longest carbon chain, also known as the parent chain. For example, an alkane having the longest carbon chain of five carbon atoms gets the parent name pentane.

The second step is to identify and name the substituents. The name of the substituent, known as a prefix, is positioned before the parent name. For example, a pentane chain having a methyl substituent gets the name methylpentane. The third step is to determine the location of the substituent by numbering the longest carbon chain. The numbering is done in such a way that the carbon on which the substituent is situated gets the lowest number. Thus, the methyl group positioned on the second carbon will obtain the name 2-methyl pentane and not 4-methyl pentane. If more than one identical or non-identical substituents are present, additional IUPAC rules apply.

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