Wikimedia
Wikipedia: Functional Group
Encyclopedia entry for functional groups that, in in organic chemistry, are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.
BBC
Bbc: Gcse Bitesize: Organic Compounds
The alkanes, alkenes, alcohols and carboxylic acids are four different homologous series of organic compounds. Their different chemical properties are due to their characteristic functional groups. This lesson focuses on Alkanes...