There are four alcohols, A, B, C and D, which are structural isomers with the molecular formula C4H10O. Alcohol A does not react with acidified potassium dichromate(VI) solution but B, C and D do. All four alcohols react with hot, concentrated sulfuric acid to form products with the molecular formula C4H8. A, C and D each give a single product in this reaction. B gives a mixture of two structural isomers, one of which shows stereoisomerism. (a) Give the skeletal formula for each of the four alcohols and complete the diagram with the names of structural isomerism shown by each linked pair of compounds. (b) (i) Give the names of the two structural isomers produced by the reaction of B with hot, concentrated sulfuric acid. (ii) State which of these two isomers shows stereoisomerism. Explain why this molecule is capable of showing stereoisomerism. (iii) Draw displayed formulae to show the two stereoisomers.

A-Level CIE Chemistry 3.5 Alcohols: There are four alcohols, A, B, C

There are four alcohols, A, B, C and D, which are structural isomers with the molecular formula C4H10O - CIE - A-Level Chemistry - Question 4 - 2015 - Paper 1

Question 4

There are four alcohols, A, B, C and D, which are structural isomers with the molecular formula C4H10O. Alcohol A does not react with acidified potassium dichromate... show full transcript

Worked Solution & Example Answer:There are four alcohols, A, B, C and D, which are structural isomers with the molecular formula C4H10O - CIE - A-Level Chemistry - Question 4 - 2015 - Paper 1

Step 1

Give the skeletal formula for each of the four alcohols and complete the diagram with the names of structural isomerism.

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Answer

The four alcohols with the molecular formula C4H10O can be represented as follows:

A:

(2-methylpropan-1-ol)
B:

(butan-1-ol)
C:

(butan-2-ol)
D:

(1-butanol)

The relationships between the alcohols are as follows:

A and B show chain isomerism.
A and C show position isomerism.
C and D show chain isomerism.
B also shows position isomerism with C and D.

Step 2

Give the names of the two structural isomers produced by the reaction of B with hot, concentrated sulfuric acid.

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Answer

The two structural isomers produced from the reaction of B (butan-1-ol) with hot, concentrated sulfuric acid are:

but-1-ene
but-2-ene

Step 3

State which of these two isomers shows stereoisomerism. Explain why this molecule is capable of showing stereoisomerism.

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Answer

The isomer that shows stereoisomerism is but-2-ene.

This molecule is capable of showing stereoisomerism because it has a double bond between two carbon atoms (C=C) with two different groups attached to each carbon atom. The presence of a double bond restricts rotation, allowing for the formation of E/Z isomers.

Step 4

Draw displayed formulae to show the two stereoisomers.

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Answer

The displayed formulae for the two stereoisomers of but-2-ene are as follows:

Stereoisomer 1:
Stereoisomer 2:

These structures can be drawn either way round as the geometrical arrangements differ.

There are four alcohols, A, B, C and D, which are structural isomers with the molecular formula C4H10O - CIE - A-Level Chemistry - Question 4 - 2015 - Paper 1

Worked Solution & Example Answer:There are four alcohols, A, B, C and D, which are structural isomers with the molecular formula C4H10O - CIE - A-Level Chemistry - Question 4 - 2015 - Paper 1

Give the skeletal formula for each of the four alcohols and complete the diagram with the names of structural isomerism.

Give the names of the two structural isomers produced by the reaction of B with hot, concentrated sulfuric acid.

State which of these two isomers shows stereoisomerism. Explain why this molecule is capable of showing stereoisomerism.

Draw displayed formulae to show the two stereoisomers.

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