Types of Structural Isomerism
- Structural isomers are compounds that have the same molecular formula but different structural formulae
- E.g. propene and cyclopropane
Both propene and cyclopropane are made up of 3 carbon and 6 hydrogen atoms but the structure of the two molecules differs
- There are three different types of structural isomerism:
- Chain isomerism
- Positional isomerism
- Functional group isomerism
Chain isomerism
- Chain isomerism is when compounds have the same molecular formula, but their longest hydrocarbon chain is not the same
- This is caused by branching
- E.g. pentane and 2,2-dimethylpropane
Both compounds are made up of the same atoms, however the longest carbon chain in pentane is 5 and in 2,2-dimethylpropane it is 3 (with two methyl branches)
Positional isomerism
- Positional isomers arise from differences in the position of a functional group in each isomer
- The functional group can be located on different carbons
- For example, butan-1-ol (or butanol) and butan-2-ol (or 2-butanol)
Both compounds have an alcohol group and are made up of 4 carbons, 10 hydrogens and one oxygen, however in butanol the functional group is located on the first carbon and in 2-butanol on the second carbon
Functional group isomerism
- When different functional groups result in the same molecular formula, functional group isomers arise
- The isomers have very different chemical properties as they have different functional groups
- For example, butanol and ethoxyethane
Both compounds have the same molecular formula however butanol contains an alcohol functional group and ethoxyethane an ether functional group