Question

Write structures of all the alkenes which on hydrogenation give 2-methylbutane.

Answer 1

Given:

On hydrogenation, alkenes add H₂ across the C=C bond without changing the carbon skeleton.

The product after hydrogenation is 2-methylbutane:

CH₃–CH(CH₃)–CH₂–CH₃

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Therefore:

All alkenes must have the same carbon skeleton as 2-methylbutane, with one C=C double bond placed at different positions.

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Possible alkenes:

1. 2-Methylbut-1-ene

Structural formula:
CH₂=C(CH₃)–CH₂–CH₃

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2. 2-Methylbut-2-ene

Structural formula:
CH₃–C(CH₃)=CH–CH₃

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Conclusion:

The alkenes which on hydrogenation give 2-methylbutane are:

• 2-Methylbut-1-ene
• 2-Methylbut-2-ene