Positional isomerism, an example of structural isomerism, occurs when functional groups are in different positions on the same carbon chain. In GCSE Chemistry, you usually meet positional isomers of alcohols and alkenes. At A Level, you find out about positional isomers involving other functional groups in aliphatic (straight- or open-chain) compounds, and in aromatic compounds.I have put models of the positional isomers of butanol, butene and methylphenol here. The first two are typical of the sort of molecules you meet in GCSE and at AS Level; you will meet aromatic compounds like methylphenol at A2 level. You should be prepared to work out positional isomers for simple organic compounds like these for your examinations, and you also need to be able to name the them at AS/A Level. You can see:
butan-1-ol
butan-2-ol
but-1-ene
but-2-ene
Note: this iscis-but-2-ene, which has a geometric isomer calledtrans-but-2-ene (selecthereto find out more)
2-methylphenol
3-methylphenol
4-methylphenol


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Rinkoo Gupta
AskIITians Faculty