Q.Explain the following giving examples:
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Start your 14-day free trial to unlock the full solution →(i) A functional group is the reactive centre that gives a compound its characteristic chemistry (e.g. -OH for alcohols). (ii) A homologous series is a family of compounds sharing that functional group, following one general formula, each differing from the next by -CH2-.
(i) Functional group: A functional group is an atom or a specific group of atoms within a molecule that is mainly responsible for its characteristic chemical properties/reactions. Different compounds sharing the same functional group tend to show similar chemical behaviour, regardless of the rest of the carbon skeleton.
Example: the -OH (hydroxyl) group in ethanol (CH3-CH2-OH) makes it an alcohol and gives it alcohol-typical reactions (e.g. reaction with sodium to release H2, esterification with acids); similarly the -COOH (carboxyl) group in acetic acid (CH3-COOH) makes it a carboxylic acid, giving it acidic reactions.
(ii) Homologous series: A homologous series is a family/group of organic compounds that:
- all contain the same functional group,
- can all be represented by the same general formula,
- have each successive member differing from the one before it by a constant -CH2- unit (14 mass units),
- show a gradual, regular change in physical properties (like melting point and boiling point) as molecular mass increases along the series,
- show broadly similar chemical properties (since the functional group is the same), …
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