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7.2: Alkane Nomenclature

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  • Since alkanes are the most fundamental types of organic compounds, their structural features (a basic carbon chain, or skeleton) provide the basis for the nomenclature of all organic compounds. The earliest nomenclature systems followed almost no systematic rules. Substances were named based on their smell, or their natural source, etc. Many of those names are still in use today and are collectively known as common names. As organic chemistry developed and structures became more complex, a systematic method for naming organic compounds became necessary. The International Union of Pure and Applied Chemistry (IUPAC) is the organism that sets the rules for nomenclature of organic compounds today. Names that follow IUPAC rules are known as systematic names, or IUPAC names.

    According to IUPAC rules, the first four alkanes are called methane, ethane, propane, and butane. They contain one, two, three, and four carbon atoms respectively, in a linear arrangement. Beginning with the fifth member of the series, pentane, the number of carbons is indicated by a greek prefix (penta, hexa, hepta, etc.). Most organic chemistry textbooks contain tables of at least the first ten members of the series, along with their structures and physical properties. Thus, the first two and most elementary rules for naming alkanes are to identify the length of the carbon chain, start the name with the appropriate greek prefix, and end the name with the suffix -ane. All this is obvious from the examples just given. Other rules are discussed next.

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