Isomerism

Isomers are compounds with the same molecular formula but different molecular formulas

When drawing structural formulas we should remember that bending the chain around does not produce a new molecule - we need to make a BRANCH in the chain

Isomers have different physical properties which depend on the strength of intermolecular forces. For isomers, the strength of intermolecular forces increases as the carbon chain length increases and decreases as the amount of chain branch9ing increases. With more branches, the molecule becomes more ‘spherical’, and there are fewer points of contact.

Unbranched molecules in close contact Branched molecules have fewer points of contact

Examples

Boiling point /ºC

Pentane, C₅H₁₂ 36

2-methylbutane, C₅H₁₂ 28

2,2-dimethylpropane, C₅H₁₂ 10

As the amount of branching increases the boiling point falls