Question

896 mL vapour of a hydrocarbon ‘A’ having carbon 87.80% and hydrogen 12.19% weighs 3.28g at STP. Hydrogenation of ‘A’ gives 2-methylpentane. Also ‘A’ on hydration in the presence of H2SO4 and HgSO4 gives a ketone ‘B’ having molecular formula C6H12O. The ketone ‘B’ gives a positive iodoform test. Find the structure of ‘A’ and give the reactions involved.

Answer 1

⇒ Molecular mass is double of the empirical formula mass.

Hence, the molecule has a five carbon chain with a methyl group at the second carbon atom.

‘A’ adds a molecule of H2O in the presence of Hg2+ and H+, it should be an alkyne. Two possible structures for ‘A’ are :

Since the ketone (B) gives a positive iodoform test, it should contain a —COCH3 group. Hence the structure of ketone is as follows :