Homologous Series & Reactions

Specification Point 9.32C:

• Recall members of a given homologous series have similar reactions because their molecules contain the same functional group and use this to predict the products of other members of these series

• Homologous series are families or groups of organic compounds that have similar features and chemical properties due to them having the same functional group.
• All members of a homologous series have:
  • The same general formula.
  • The difference in the molecular formula between one member and the next is CH₂.
  • Gradation in their physical properties.
  • Same functional group.
  • Similar chemical properties.
• The chemistry of homologous series is therefore determined by the functional group.
• We can use this to predict how molecules further down a homologous series will react.
• For example we know that ethene will decolourise bromine water, so we can predict that hexene and septene will do the same, even though they are bigger molecules.

• This is due the the alkene functional group, the C=C double bond, which is present in all alkenes.