Grade 12 Physical Sciences · Matter and Materials

Identify and draw structural isomers

Recognise or draw compounds with the same molecular formula but a different structure (butane and methylpropane are both C₄H₁₀).

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Isomers Organic Chemistry Grade 12 IntroductionMiss Martins Maths and Science

Isomers Organic Chemistry Grade 12Kevinmathscience

Positional isomers and Chain Isomers Grade 12 Organic Chemistry PRACTICEMiss Martins Maths and Science

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Question 1.3 · November 2025 · Paper 2 · National (DBE) · 2 marks

Various options are provided as possible answers to the following questions. Each question has only ONE correct answer.

1.3 Which of the following statements ALWAYS apply to compounds that are structural isomers of one another?

(i) They belong to the same homologous series.
(ii) They have the same structural formula.
(iii) They have the same molecular formula.(2)

A (iii) only
B (i) and (iii) only
C (i) and (ii) only
D (i), (ii) and (iii)

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More past paper questions: identify and draw structural isomers

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3. Question 2.2.2 · May/June 2024 · Paper 2 · National (DBE) · 2 marks
The letters A to H in the table below represent eight organic compounds.
2.2 Write down the letter(s) for:
2.2.2 TWO compounds that are CHAIN ISOMERS of each other(2)
Show the memo (1 tick)Memo
1. ✓
  Chain isomersD and H
  2 marks · Identify and draw structural isomers
4. Question 2.5.2 · May/June 2025 · Paper 2 · National (DBE) · 2 marks
The letters A to F in the table below represent organic compounds.
2.5 Write down the IUPAC name of:
2.5.2 The POSITIONAL isomer of compound D(2)
Show the memo (2 ticks)Memo
1. ✓
  Correct stem and substituentsStem and substituents: methyl and propanol
  1 mark · Identify and draw structural isomers
2. ✓
  Fully correct name2-methylpropan-1-ol
  1 mark · Write IUPAC names
5. Question 2.2.4 · November 2025 · Paper 2 · National (DBE) · 4 marks
The letters A to G in the table below represent organic compounds.
2.2 Write down the:
2.2.4 STRUCTURAL FORMULAE of two STRAIGHT CHAIN positional isomers of compound D(4)
Show the memo (4 ticks)Memo
1. ✓
  Isomer 1: hydroxyl group on the 1st C-atomButan-1-ol: the $- OH$ group on the first carbon of a straight chain of 4 carbons.
  1 mark · Identify and draw structural isomers
2. ✓
  Isomer 1: whole structure correct $H-O-CH_{2} -CH_{2} -CH_{2} -CH_{3}$ drawn with every bond and every H atom shown.
  1 mark · Draw structural formulae
3. ✓
  Isomer 2: hydroxyl group on the 2nd C-atomButan-2-ol: the $- OH$ group on the second carbon of a straight chain of 4 carbons.
  1 mark · Identify and draw structural isomers
4. ✓
  Isomer 2: whole structure correct $CH_{3} -CH(OH)-CH_{2} -CH_{3}$ drawn with every bond and every H atom shown.
  1 mark · Draw structural formulae
6. Question 2.2.3 · May/June 2023 · Paper 2 · National (DBE) · 2 marks
Study the table below and answer the questions that follow.
2.2 Write down the:
2.2.3 IUPAC name of the POSITIONAL isomer of compound B(2)
Show the memo (2 ticks)Memo
1. ✓
  Correct stem: propanolPropan-2-ol / 2-propanol
  
  Correct stem i.e. propanol.
  1 mark · Write IUPAC names
2. ✓
  IUPAC name completely correct (OH moved to C2)Propan-2-ol / 2-propanol
  1 mark · Identify and draw structural isomers

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