O Levels Chemistry (5070)•5070/11/M/J/18
Explanation
Identifying the branched C4H8 alkene from butane cracking Steps:
- Z decolours bromine water, indicating an alkene with C=C bond.
- Hydrogenation of Z yields butane (C4H10) as the only product, so Z has formula C4H8.
- Z has branched structure, matching 2-methylpropene among C4H8 isomers.
- Cracking C4H10 (isobutane isomer) yields this branched alkene Z.
Why D is correct:
- D is (CH3)2C=CH2, the branched C4H8 alkene that fits all properties per alkene general formula CnH2n.
Why the others are wrong:
- A (CH2=CHCH2CH3) is straight-chain 1-butene.
- B (CH3CH=CHCH3) is straight-chain 2-butene.
- C (cyclobutane or similar) lacks C=C unsaturation or branching.
Final answer: D
Topic: Alkenes
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