Chain isomerism

Chain isomers have the same molecular formula, but the way their carbon atoms are joined together differs from isomer to isomer. Alkane molecules with four or more carbon atoms have chain isomers. In these isomers, the carbon atoms are bonded together in different ways to produce branches.

What is here?

You can see models of the three chain isomers of pentane, C₅H₁₂. You can also see the structural and displayed formulae for these alkanes.

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2-methylbutane

2,2-dimethylpropane

pentane

Branches

Pentane is the unbranched “straight chain” isomer of C₅H₁₂. The other two isomers are branched:

2-methylbutane has one branch
2,2-dimethylpropane has two branches.

Each of these branches contains one carbon atom and is a methyl group, —CH₃.

Structural and displayed formulae

A structural formula shows the number of atoms of each element in a molecule, and their positions in the molecule.

A displayed formula shows the same information as a structural formula, but in addition it shows the bonds between the atoms.

Name of alkane	Structural formula	Displayed formula
2-methylbutane	(CH₃)₂CHCH₂CH₃
2,2-dimethylpropane	C(CH₃)₄
pentane	CH₃(CH₂)₃CH₃