A functional group is an atom or group of atoms in a molecule that is responsible for the characteristic chemical reactions of that molecule.The rest of the molecule is usually an unreactive hydrocarbon chain, so compounds with the same functional group react in similar ways, whatever the length of their chain. Ethanol and propan-1-ol, for example, both contain -OH and undergo the same reactions.Common functional groups:Alkene: C=C double bond, e.g. propene, CH2=CHCH3.
Alcohol: hydroxyl group -OH, e.g. ethanol, CH3CH2OH.
Halogenoalkane: a halogen atom bonded to carbon, C-X, e.g. bromoethane, CH3CH2Br.
Aldehyde: -CHO, a C=O group at the end of a chain, e.g. ethanal, CH3CHO.
Ketone: C=O within the chain, e.g. propanone, CH3COCH3.
Carboxylic acid: carboxyl group -COOH, e.g. ethanoic acid, CH3COOH.
Ester: -COO- between two carbon groups, e.g. methyl ethanoate, CH3COOCH3.
Amine: -NH2, e.g. methylamine, CH3NH2.Alkanes have no functional group, which is one reason they are unreactive.Worked example: identify the functional groups in HOCH2CH=CH2. It contains a hydroxyl group (-OH) and a C=C double bond, so it will show the reactions of both an alcohol and an alkene.The functional group also decides the ending or prefix used in the compound's name, for example -ol for alcohols and bromo- for bromine.
Alcohol: hydroxyl group -OH, e.g. ethanol, CH3CH2OH.
Halogenoalkane: a halogen atom bonded to carbon, C-X, e.g. bromoethane, CH3CH2Br.
Aldehyde: -CHO, a C=O group at the end of a chain, e.g. ethanal, CH3CHO.
Ketone: C=O within the chain, e.g. propanone, CH3COCH3.
Carboxylic acid: carboxyl group -COOH, e.g. ethanoic acid, CH3COOH.
Ester: -COO- between two carbon groups, e.g. methyl ethanoate, CH3COOCH3.
Amine: -NH2, e.g. methylamine, CH3NH2.Alkanes have no functional group, which is one reason they are unreactive.Worked example: identify the functional groups in HOCH2CH=CH2. It contains a hydroxyl group (-OH) and a C=C double bond, so it will show the reactions of both an alcohol and an alkene.The functional group also decides the ending or prefix used in the compound's name, for example -ol for alcohols and bromo- for bromine.