A2 · Practice questions · A Level functional groups and naming

Name the new groups.

Six original Cambridge-style questions on A Level functional groups and naming.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Group, parent, locants.

Phenol: OH directly on the ring; that carbon is C1.
Acyl chloride, amide, nitrile: count the functional carbon in the stem.
Amines: 1, 2 or 3 carbon groups on N.
Ring locants: lowest set, alphabetical order.

Recall

[4 marks]

Name the homologous series of each compound: (a) C₆H₅Br, (b) CH₃CH₂COCl, (c) CH₃CH₂CONH₂, (d) CH₃CH₂CN.

(a) halogenoarene (bromobenzene). ✓
(b) acyl chloride (propanoyl chloride). ✓
(c) amide (propanamide). ✓
(d) nitrile (propanenitrile). ✓

Analysis

[3 marks]

Classify each amine as primary, secondary or tertiary: (a) CH₃CH₂NHCH₃, (b) C₆H₅NH₂, (c) (C₂H₅)₃N.

(a) secondary: two carbon groups (ethyl and methyl) on N. ✓
(b) primary: one carbon group (phenyl) on N; this is phenylamine. ✓
(c) tertiary: three ethyl groups on N. ✓

Recall

[2 marks]

Draw or describe 1,3-dinitrobenzene and explain why it is not called 1,5-dinitrobenzene.

A benzene ring with NO₂ groups on carbons 1 and 3, with one ring carbon between them. ✓
Numbering the other way round gives 1,5, but the rule is to use the lowest set of locants. ✓

Calculation

[2 marks]

Calculate the percentage by mass of nitrogen in 1,3-dinitrobenzene, C₆H₄(NO₂)₂.

M_r = 6(12.0) + 4(1.0) + 2(14.0) + 4(16.0) = 168.0. ✓
%N = 28.0 ÷ 168.0 × 100 = 16.7%. ✓

Explain

[2 marks]

Explain why C₆H₅OH is a phenol but C₆H₅CH₂OH is an alcohol.

In C₆H₅OH the OH is bonded directly to a carbon of the benzene ring. ✓
In C₆H₅CH₂OH the OH is on a CH₂ side-chain carbon, so it is a primary alcohol (phenylmethanol). ✓

Analysis

[3 marks]

2-aminopropanoic acid has the formula CH₃CH(NH₂)COOH. Identify its two functional groups and explain the number 2 in the name.

It has a primary amine group, –NH₂, and a carboxylic acid group, –COOH. ✓
The chain is numbered from the COOH carbon, which is C1. ✓
The NH₂ is on C2, the carbon next to COOH, so it is a 2-amino acid. ✓

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