Isomers

Isomers

Isomers are molecules with the same molecular formula, but different arrangements of atoms. There are different types of isomers, shown by the diagram on the right.

Functional Isomerism

Functional isomerism, an example of structural isomerism, occurs substances have the same molecular formula but different functional groups. This means that functional isomers belong to different homologous series.

ethanol	methoxymethane	C2H6O
		Alcohols have the hydroxyl group, ?OH. Ethers have the functional group R?O?R'.
propanal	propanone (acetone)	C3H6O
		Aldehydes and ketones both have the carbonyl group C=O. In ketones this is attached to two carbon atoms; in aldehydes it is attached to 1 or 2 hydrogen atoms.

Positional Isomerism

Positional isomerism, an example of structural isomerism, occurs when functional groups are in different positions on the same carbon chain.

butan-1-ol	butan-2-ol
but-1-ene	but-2-ene	Note: this is cis-but-2-ene, which has a geometric isomer called trans-but-2-ene (select here to find out more)
2-methylphenol	3-methylphenol	4-methylphenol

Chain Isomerism

Chain isomerism occurs when the way carbon atoms are linked together is different from compound to compound. It is an example of structural isomerism, and is also called nuclear isomerism.

pentane

2-methylbutane

2,2-dimethylpropane