A functional group is the atom or group of atoms that gives a homologous series its characteristic chemical reactions.
A functional group is the atom or group of atoms that gives a homologous series its characteristic chemical reactions. Malay: kumpulan berfungsi · Chinese: 官能团.
The functional group is the reactive part of the molecule, so every member of a series carries the same group and therefore reacts in the same way. The long carbon chain attached to it is largely a spectator during reactions; it changes the physical properties as it lengthens but not the chemistry. This is why knowing the functional group lets you predict a whole family’s behaviour at once. The alcohols are defined by the hydroxyl group –OH, the carboxylic acids by the carboxyl group –COOH, and the alkenes by the carbon–carbon double bond, C=C. When you name a compound, the suffix of its name, such as -ol, -oic acid or -ene, points straight to the functional group, so the name itself tells you how the compound will react.
Example. Ethanol and propan-1-ol both contain the –OH functional group, so both react with sodium to give hydrogen, both can be oxidised to a carboxylic acid, and both can be dehydrated to an alkene. Their chains differ, but the chemistry the –OH controls is the same.
Confusion to avoid. Do not confuse the functional group with the general formula. The general formula counts the atoms; the functional group is the specific reactive site. Two compounds can have similar formulae yet different functional groups, for example C₂H₆O can be ethanol (with –OH) or an ether (with –O–), and these behave quite differently.
The functional group is the single most useful idea for organising this chapter: pair each series with its group and its reactions, and the vocabulary that SPM Chemistry tests falls into a tidy, memorable pattern.
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