One mole of HBr adds to buta-1,3-diene at -80 degC (kinetic control). The major product is:

NEET levelSingle correct optionDifficulty 1 of 3hc188

One mole of $HBr$ adds to buta-1,3-diene at $- 8 0^{\circ} C$ (kinetic control). The major product is:

Protonation at C1 gives the allylic cation

CH X_{3} - CH X^{+} - CH = CH X_{2}

. At low temperature the faster 1,2-addition dominates, giving

CH X_{3} - CHBr - CH = CH X_{2}

, 3-bromobut-1-ene.