Question

Reaction of one molecule of $HBr$ with one molecule of $1,3$ -butadiene at $40^{\circ }C$ 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

Answer: (C)

$1$-bromo-$2$-butene under thermodynamically controlled conditions

Under mild conditions (temprature $\approx -80^{\circ }C$ ) kinetic product is the $1,2$ -addition product and under vigorous conditions,. (temp. $\approx 40^{\circ }C$ ) thermodynamic product is the $1,4$ addition product.
Thus, $1$ -bromo $-2$ - butene is the major product under given condition.