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Chain isomerism

What is it?

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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chemdoodle.png atom labels
ball and stick model
space-filling model
perspective view





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.

In each case, the branch contains one carbon atom and is a methyl group, —CH3.

Structural and displayed formulae

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