Topic 2 of 34
Recognise the functional group before choosing a reaction
The same atom, such as nitrogen or oxygen, behaves differently in different bonding environments.
A-Level 9476 (2026-2027)
Recognise the functional group before choosing a reaction
The same atom, such as nitrogen or oxygen, behaves differently in different bonding environments.
| Class | Recognisable group or formula | Example name and structure |
|---|---|---|
| Alkane | Acyclic saturated: CnH2n+2; only C-C and C-H single bonds. | Ethane, CH3CH3. |
| Alkene | C=C; an acyclic monoalkene has CnH2n. | Ethene, CH2=CH2. |
| Arene | An aromatic ring; do not assign every arene one universal alkene-like formula. | Benzene, C6H6; methylbenzene, C6H5CH3. |
| Halogenoalkane / halogenoarene | R-X / Ar-X; X = halogen. | Bromoethane, CH3CH2Br / chlorobenzene, C6H5Cl. |
| Alcohol / phenol | OH on a saturated carbon / OH directly on an aromatic ring. | Ethanol, CH3CH2OH / phenol, C6H5OH. |
| Aldehyde / ketone | -CHO / -CO- between two carbon groups. | Ethanal, CH3CHO / propanone, CH3COCH3. |
| Carboxylic acid | -COOH. | Ethanoic acid, CH3COOH; benzoic acid, C6H5COOH. |
| Acyl chloride | -COCl; chlorine attached to the carbonyl carbon. | Ethanoyl chloride, CH3COCl. |
| Ester | -COOR. | Ethyl ethanoate, CH3COOCH2CH3; name the alcohol-derived alkyl group first. |
| Class | Recognisable structure | Example and naming clue |
|---|---|---|
| Amine | RNH2, R2NH or R3N; nitrogen lone pair not directly attached to a carbonyl. | Ethylamine, CH3CH2NH2; phenylamine, C6H5NH2. |
| Amide | -CONH2, -CONHR or -CONR2. | Ethanamide, CH3CONH2; N-methylethanamide, CH3CONHCH3. |
| Amino acid | Both amino and carboxylic acid groups. | Aminoethanoic acid, H2NCH2COOH. |
| Nitrile | -C≡N; the nitrile carbon belongs to the carbon skeleton. | Propanenitrile, CH3CH2CN, contains three carbons. |
R is a general alkyl or organic group and Ar denotes an aromatic group. They are placeholders, not atoms. For simple acyclic saturated monofunctional examples, alcohols have CnH2n+2O, aldehydes/ketones CnH2nO and monocarboxylic acids/esters CnH2nO2. A ring, extra multiple bond or additional group changes these relations, so use the structural group when the scope is wider.
Check your understandingWhy do CH3CH2OH, C6H5OH and CH3COOH need different reaction predictions even though each has an O-H bond?Think it through, then reveal the answer
They are an alcohol, phenol and carboxylic acid. The groups attached to oxygen change electron delocalisation and the stability of the conjugate base, so their acidities and characteristic reactions differ.