Question

Reaction of one molecule of HBr with one molecule of 1, 3-butadiene at 40°C gives predominantly
(a) 1-bromo-2-butene under kinetically controlled conditions
(b) 3-bromobutene under thermodynamically controlled conditions
(c) 1-bromo-2-butene under thermodynamically controlled conditions
(d) 3-bromobutene under kinetically controlled conditions

Answer 1

Reaction of one molecule of HBr with one molecule of 1, 3-butadiene at 40°C gives predominantly   (c) 1-bromo-2-butene under thermodynamically controlled conditions .

- The possible products are :

CH2=CH-CH=CH2 + HBr ---> CH3-CHBr-CH=CH2 + CH3CH=CH-CH2Br

- Under mild conditions (T ≈ - 80°C) kinetic product is the 1, 2-addition product and under vigorous conditions,. (T ≈ 40°C) thermodynamic product is the 1 , 4-addition product.

- Only option which fulfills the criteria is (c)

- Thus, 1-bromo -2- butene is the major product under given condition.