Isomers, homologous series and organic properties

Isomers, homologous series and organic properties

Isomers have the same molecular formula but different structural arrangements, so they can have different physical properties and reactions. Chain isomers differ in carbon skeleton, position isomers differ in the position of a functional group or multiple bond, and functional-group isomers have different functional groups. Homologous-series trends arise from increasing molecular size and stronger London dispersion forces, but functional group and branching also matter. When comparing boiling points or reactions, write the structure instead of relying only on a molecular formula. The formula C₄H₁₀, for example, can represent two chain isomers.

Work it through

Butane and 2-methylpropane both have C₄H₁₀. Their connectivity differs, so they are structural isomers. A question asking for an isomer requires the same formula but a different valid arrangement; simply redrawing the same chain in a new orientation is not a new isomer.

Mastery target

Recognise and draw simple structural isomers, relate homologous-series structure to properties and explain why formula alone may not determine behaviour.