Answer: D. Addition of water across C=C places H on one carbon and OH on the other. Only ONE alcohol forms when the two carbons of the C=C are identical — i.e. they carry the same substituents — because either orientation of H–OH addition gives the same product.
A: \(\text{CH}_3\text{CH}=\text{CH}_2\) (propene). Ends differ → two alcohols possible (propan-1-ol or propan-2-ol).
B: \(\text{CH}_3\text{CH}_2\text{CH}=\text{CH}_2\) (but-1-ene). Ends differ → two alcohols (butan-1-ol or butan-2-ol).
C: \((\text{CH}_3)_2\text{C}=\text{CHCH}_3\) (2-methylbut-2-ene). Two C atoms of the C=C have different substituents → two alcohols.
D: \((\text{CH}_3)_2\text{C}=\text{C(CH}_3)_2\) (2,3-dimethylbut-2-ene). Both C atoms of the C=C carry exactly two methyl groups — identical environments. Either way of adding H–OH gives the same 2,3-dimethylbutan-2-ol. ✓
Only D's symmetric alkene gives a single alcohol.
Every O Level Pure Chemistry TYS MCQ solution video, plus full Sec 3 / Sec 4 topic recordings.
Find out more