JEE Main Chemistry question

Reaction of one molecule of HBr with one molecule of 1,3-butadiene at 40 °C gives predominantly [AIEEE 2005]

(A)1-bromo-2-butene (1,4-addition product) under kinetically controlled conditions
(B)3-bromobutene (1,2-addition product) under thermodynamically controlled conditions
(C)3-bromo-1-butene (1,2-addition product) under kinetically controlled conditions
(D)1-bromo-2-butene (1,4-addition product) under thermodynamically controlled conditionsCorrect

Answer: (D)

Solution

Protonation of the conjugated diene gives an allylic cation delocalised over C-2 and C-4; at low temperature (kinetic control) Br attacks the more accessible, less hindered C-2 to give the 1,2-adduct (3-bromobut-1-ene),

See the full step-by-step solution

Create a free account to read the complete working, and practise questions like this in a timed test.

Create a free account

Question ID VK-142229