How many structural isomers does C₅H₁₂ have, and what are they?

C₅H₁₂ has three structural isomers. The isomers are pentane, 2-methylbutane and 2,2-dimethylpropane.

Why does 2,2-dimethylpropane boil at a lower temperature than pentane?

Branching makes the molecule more compact, so there is less surface contact between neighbouring molecules. The London forces are weaker and less energy is needed to separate the molecules.

Name the five structural isomers of C₆H₁₄.

Hexane, 2-methylpentane and 3-methylpentane are three of the five isomers. 2,2-Dimethylbutane and 2,3-dimethylbutane complete the set.

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Organic Chemistry

Structural isomerism and E/Z isomerism

3 things to know
A2 2

Overview

Chain, position and functional group isomers of alkanes, alcohols and carbonyl compounds, stereoisomers, the conditions for E/Z isomerism, and cis and trans names.

What you need to know

Answer each one before you reveal it.

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Key term

What are structural isomers?

Key term

What are the three types of structural isomerism?

Key term

Name the two structural isomers of C₄H₁₀.

Questions from this subtopic

Each one with the model answer underneath.

1
What are structural isomers?
Model answer
Structural isomers have the same molecular formula but different structural formulae. The atoms are bonded together in a different order.
2
What are the three types of structural isomerism?
Model answer
Chain isomers differ in the branching of the carbon chain. Position isomers differ in where the functional group sits, and functional group isomers have different functional groups.
3
Name the two structural isomers of C₄H₁₀.
Model answer
The isomers of C₄H₁₀ are butane and 2-methylpropane. Butane is an unbranched chain, while 2-methylpropane has a methyl branch on a three-carbon chain.
4
How many structural isomers does C₅H₁₂ have, and what are they?
Model answer
C₅H₁₂ has three structural isomers. The isomers are pentane, 2-methylbutane and 2,2-dimethylpropane.
5
Why does 2,2-dimethylpropane boil at a lower temperature than pentane?
Model answer
Branching makes the molecule more compact, so there is less surface contact between neighbouring molecules. The London forces are weaker and less energy is needed to separate the molecules.
6
Name the five structural isomers of C₆H₁₄.
Model answer
Hexane, 2-methylpentane and 3-methylpentane are three of the five isomers. 2,2-Dimethylbutane and 2,3-dimethylbutane complete the set.

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