JEE Advanced · 2011 · 10 Apr 2011 · Paper 1 · Haloalkanes and Haloarenes

The total number of alkenes possible by dehydrobromination of 3-bromo-3-cyclopentylhexane using alcoholic KOH is

Answer: 5

Solution

3-bromo-3-cyclopentylhexane has the structure with Br at the tertiary carbon (C-3) bearing a cyclopentyl group and two ethyl groups.

Dehydrobromination can occur by removing H from adjacent carbons (C-2 or C-4), and also from the cyclopentyl ring.

Possible alkenes:

From C-2: E and Z isomers (2 alkenes)
From C-4: E and Z isomers (2 alkenes)
From cyclopentyl ring: 1 alkene (exocyclic double bond)

Total = 2 + 2 + 1 = 5 alkenes

JEE Advanced · 2011 · 10 Apr 2011 · Paper 1 · Integer answer

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