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9476 / 2027
Organic Chemistry

Lesson 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)

  • I can interpret, name and represent the specified organic families.Syllabus

    Syllabus 9476, 11.1(a). Interpret, name and represent the specified organic families.

  • I can use the specified reaction terminology.Syllabus

    Syllabus 9476, 11.3(a). Use the specified reaction terminology.

Recognise the functional group before choosing a reaction

The same atom, such as nitrogen or oxygen, behaves differently in different bonding environments.

Hydrocarbons and oxygen/halogen families
ClassRecognisable group or formulaExample name and structure
AlkaneAcyclic saturated: CnH2n+2; only C-C and C-H single bonds.Ethane, CH3CH3.
AlkeneC=C; an acyclic monoalkene has CnH2n.Ethene, CH2=CH2.
AreneAn aromatic ring; do not assign every arene one universal alkene-like formula.Benzene, C6H6; methylbenzene, C6H5CH3.
Halogenoalkane / halogenoareneR-X / Ar-X; X = halogen.Bromoethane, CH3CH2Br / chlorobenzene, C6H5Cl.
Alcohol / phenolOH 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.
Nitrogen families
ClassRecognisable structureExample and naming clue
AmineRNH2, 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 acidBoth 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 stands for any alkyl or organic group, and Ar stands for an aromatic group. They are labels, not atoms. For simple open-chain saturated compounds with one functional group, alcohols are CnH2n+2O, aldehydes and ketones are CnH2nO, and carboxylic acids and esters are CnH2nO2. A ring, an extra double bond or another group changes these formulae, so use the structure when the molecule is more complex.

Check your understanding

CH3CH2OH, C6H5OH and CH3COOH each have an O-H bond. Why do they need different reaction predictions?

  1. They have different numbers of carbon atoms, so their boiling points and hence their reactions differ.
  2. Their O-H bonds have different lengths, so the one with the longest bond reacts fastest in every reaction.
  3. They are an alcohol, a phenol and a carboxylic acid; the group on the oxygen changes delocalisation and anion stability.
Show the answer

They are an alcohol, a phenol and a carboxylic acid; the group on the oxygen changes delocalisation and anion stability.

In phenol and in a carboxylic acid, the negative charge of the conjugate base can be delocalised (into the ring, or over two oxygens). The alkoxide cannot. So their acidities and typical reactions differ.