A LevelChemistryCIETopic Questions13. An Introduction to AS Level Organic Chemistry13.4 Isomerism: Structural Isomerism & Stereoisomerism

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First teaching 2023

First exams 2025

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Isomerism: Structural Isomerism & Stereoisomerism (CIE A Level Chemistry)

Topic Questions

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1a3 marks

State the three different types of structural isomerism.

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1b2 marks

State the type of isomerism that occurs between the following pairs of compounds.

 
i)
2-methylpentane and 2,3-dimethylbutane.
 
[1]
 
ii)
Butan-1-ol and butan-2-ol
 
[1]

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1c3 marks

Compounds A to F are shown in Fig 1.1. 

4-1_q3d-e-ocr-a-as--a-level-easy-sq 
Fig 1.1
 
i)
State the IUPAC name for compound B.
[1]
 
ii)
State the type of structural isomerism that occurs between compounds A and D.
[1]
 
iii)
State the type of structural isomerism that occurs between compounds C and E.
[1]

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2a1 mark
Name the two types of stereoisomers.
 

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2b1 mark

Describe what a chiral centre is.

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2c1 mark

The structure of one optical isomer of a chlorofluorocarbon is shown in Fig 2.1.

 
1-2
 
Fig 2.1
 

Draw the structure of the other enantiomer.

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2d1 mark

The skeletal structure of a halogenoalkane is shown in Fig 2.2.

 
egodLOJO_5
 
Fig 2.2 
 

Explain why the carbon labelled a cannot be a chiral centre.

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1a3 marks

The organic compounds in Fig 1.1 are all made by living organisms.

s55z~ain_10

Fig. 1.1

i)
Give the name of compound A.
 
[1]
 
ii)
Compound A has two chiral centres and forms stereoisomers.
 
Draw one pair of optical isomers of compound A using the conventional three-dimensional representation.
 
 

 

 

 

 

 
 
[2]

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1b3 marks

Compounds B, C, D and E all show the same type of isomerism.

 

Circle the functional group(s) responsible for this isomerism on the molecules in Fig 1.1.

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1c4 marks

Compound D reacts with hydrogen chloride to form two products.

 
i)
Fully name the type of mechanism for this reaction.
 
[1]
 
ii)
One of the products formed exists as a pair of stereoisomers.
 
Draw three-dimensional diagrams of the pair of stereoisomers formed during this reaction.
 
Indicate with an asterisk (*) the chiral centre on one of the structures drawn.
 
 

 

 

 

 

 
 
[3]

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1d1 mark

Name the type of reaction occurring when compound E reacts to form methanol and deca-2,4-dienoic acid.

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1a3 marks

A chemist is analysing a collection of organic compounds.

Some of these compounds are shown in Table 1.1.

 Table 1.1
Compound IUPAC name Displayed formula Skeletal formula
1 Z-2-chloro-but-2-en-1-ol 2-chloro-but-2-en-1-ol-displayed 2-chloro-but-2-en-1-ol-skeletal
2 2-chloropropanal  

 

 

 
3   _z_Z1otn_3-bromo-2-methylpropan-1-ol-displayed  
4  

 

 

 

 3-methyl-but-2-enoic-acid-skeletal
  
 

Complete Table 1.1.

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1b1 mark

State the empirical formula of compound 1.

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1c4 marks

Explain why compound 1 exists as two stereoisomers, but compound 4 does not.

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1d4 marks

Compounds 2 and 3 both exhibit the same type of isomerism.

 
i)
State the type of isomerism shown by compounds 2 and 3.
 
[1]
 
ii)
Draw the two isomers of compound 2 to explain how this type of isomerism occurs.
 
[3]

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2a3 marks

There are many different chemicals with the same molecular formulae but different arrangements of atoms in three-dimensional space. 

i)
Name the shortest straight-chain alkane to have structural isomers and the isomer.
 
[2]
 
ii)
State the type of isomerism shown by the isomers in part (i).
 
[1]

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2b7 marks

C4H8 exists as several isomers.

 
i)
Name the homologous series that C4H8 belongs to.
 
 [1]
 
ii)
Draw the skeletal formulae of two cyclic C4H8 isomers and two C4H8 isomers that show cis / trans isomerism.
 
[4]
 
iii)
There are two unsaturated C4H8 isomers that do not show cis / trans isomerism. Name these isomers and explain why they do not show cis / trans isomerism.
 
[2]

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2c6 marks

Draw the displayed formulae of the following compounds and, where appropriate, identify any chiral centres. 

  • 2,4-dimethylhexan-3-ol
  • 2,4-dimethyl-3-chloropentane
  • 2-aminobutane

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2d2 marks

1-bromopropan-1-ol exhibits optical isomerism.

 

Draw 3D representations of the two enantiomers of 1-bromopropan-1-ol.

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3a2 marks

Butan-2-ol is used as a solvent, in industrial cleaners, in paint removers and in the manufacture of other chemicals such as butanone.

Draw the fully displayed formula of butan-2-ol and the positional isomer of butan-2-ol.

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3b2 marks

Name the branch chain isomers of butan-2-ol.

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3c2 marks

Explain why butan-2-ol does not exhibit stereoisomerism.

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