Structural isomerism

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Structural isomerism is a form of isomerism in which molecules with the same molecular formula have atoms bonded together in different orders, as opposed to stereoisomerism.

In chain isomerism chain isomers have components of the chain distinctly ordered to create different structures. For example 3-methylpentane is an isomer of 2-methylpentane. Pentane exists as three isomers: n-pentane, isopentane and neopentane.

In position isomerism positional isomers occur when a functional group changes position on the chain. In the diagram, 2-hydroxypentane has become 3-hydroxypentane. Many aromatic isomers exist because substituents can be positioned on different parts of the benzene ring. Only one isomer of phenol or hydroxybenzene exists but cresol or methylphenol has three isomers where the additional methyl group can be placed on three different positions on the ring. Xylenol has one hydroxyl group and two methyl groups and a total of 6 isomers exist.

Image:Position isomer.png

In functional group isomerism a functional group splits up and becomes a different group. Here is an example of functional group isomerism: take cyclohexane, C₆H₁₂ and 1-Hexene, also C₆H₁₂. These two are considered functional group isomers because cyclohexane is an alkane and 1-Hexene is an alkene. Both must have the same molecular formula.

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