Name the three types of structural isomerism.

Chain, position and functional group isomerism.

What are position isomers? Give an example.

Same carbon skeleton and functional group, but the group is in a different position, e.g. propan-1-ol and propan-2-ol.

What are chain isomers? Give an example.

Different carbon skeletons, e.g. butane and 2-methylpropane.

Give a pair of functional group isomers.

But-1-ene and cyclobutane, or propan-1-ol and methoxyethane.

How many structural isomers have the formula C₅H₁₂?

Three: pentane, 2-methylbutane and 2,2-dimethylpropane.

What are stereoisomers?

Compounds with the same structural formula but a different arrangement of atoms in space.

Why does a C=C bond allow E/Z isomerism?

Rotation about the C=C bond is restricted, so groups are fixed on one side or the other.

What is the condition for a molecule to show E/Z isomerism?

Each carbon atom of the C=C must be bonded to two different atoms or groups.

The higher-priority groups are on the same side of the C=C bond.

The higher-priority groups are on opposite sides of the C=C bond.

How do you decide which group has the higher priority?

The group whose first atom has the higher atomic number (CIP rules).

Which isomers of C₄H₈ show E/Z isomerism?

Only but-2-ene, which has two forms, (E) and (Z).

Isomerism: structural and E/ZEdexcel A-Level Chemistry: Flashcards

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What are structural isomers?

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What are structural isomers?: Compounds with the same molecular formula but different structural formulae.
Name the three types of structural isomerism.: Chain, position and functional group isomerism.
What are position isomers? Give an example.: Same carbon skeleton and functional group, but the group is in a different position, e.g. propan-1-ol and propan-2-ol.
What are chain isomers? Give an example.: Different carbon skeletons, e.g. butane and 2-methylpropane.
Give a pair of functional group isomers.: But-1-ene and cyclobutane, or propan-1-ol and methoxyethane.
How many structural isomers have the formula C₅H₁₂?: Three: pentane, 2-methylbutane and 2,2-dimethylpropane.
What are stereoisomers?: Compounds with the same structural formula but a different arrangement of atoms in space.
Why does a C=C bond allow E/Z isomerism?: Rotation about the C=C bond is restricted, so groups are fixed on one side or the other.
What is the condition for a molecule to show E/Z isomerism?: Each carbon atom of the C=C must be bonded to two different atoms or groups.
What does Z mean?: The higher-priority groups are on the same side of the C=C bond.
What does E mean?: The higher-priority groups are on opposite sides of the C=C bond.
How do you decide which group has the higher priority?: The group whose first atom has the higher atomic number (CIP rules).
Which isomers of C₄H₈ show E/Z isomerism?: Only but-2-ene, which has two forms, (E) and (Z).

Exam questions on Isomerism: structural and E/Z

A chemist is cataloguing the isomers of the alkane C₅H₁₂ and of the haloalkane C₄H₉Br.
Give the IUPAC names of the two branched isomers of C₅H₁₂.2 marks
A student is studying alkenes with the molecular formulae C₄H₈ and C₅H₁₀, and how the arrangement of groups around the carbon-carbon double bond affects their properties.
Explain what causes E/Z isomerism and state the condition on the groups attached to the C=C bond for a molecule to show it.2 marks
Alkenes with the molecular formula C₅H₁₀ are used as models to study isomerism. Ignore cyclic compounds in this question.
Give the structural formula and name of each unbranched alkene with molecular formula C₅H₁₀. State which one shows E/Z isomerism, with a reason.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).