Coding for branched chains

2 marks · Easy

The structural formula for a hydrocarbon is shown below. The main chain is numbered from left to right.

Diagram: Main chain has five carbon atoms. A methyl group is attached to carbon 2.

Give the position of the methyl side chain and write the IUPAC name for this hydrocarbon.

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2-methylpentane

Also accept: 2-methylpentane

Common mistakes: 4-methylpentane; pentane

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Marking points

M1 · 1 mark · Correct identification of position: methyl group at carbon 2.

A1 · 1 mark · Correct systematic name: 2-methylpentane. (follow-through)

Worked solution

The molecule has a main chain of 5 carbons (pentane). The methyl side chain is attached to carbon 2. Therefore, the IUPAC name is 2-methylpentane.