1.3: Alkyl Substituents

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Page ID: 222784

Rebekah O'Donnell
Boston University via OpenStax CNX

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Learning Objective

How to name organic molecules with alkyl substituents

An alkane can be appended onto an existing chain to create a branched molecule. This branched piece of the molecule is called a substituent. A substituent made from an alkane is called an alkyl group. Alkyl groups are named similarly to unbranched alkane chains.

Alkane	Condensed Structure	Alkyl Group	Condensed Structure
Methane	CH₄	Methyl	CH₃-
Ethane	CH₃CH₃	Ethyl	CH₃CH₂-
Propane	CH₃CH₂CH₃	Propyl	CH₃CH₂CH₂-
Butane	CH₃CH₂CH₂CH₃	Butyl	CH₃CH₂CH₂CH₂-

Alkyl groups can also be branched. For example, there are three constitutional isomers of the butyl substituent. In these diagrams, the negative charge on the carbon indicates the site of the bond from the substituent to the rest of the molecule.