Answer:
The major product and the mechanism is shown below.
Explanation:
In the reaction of 1,3-butadiene, with one equivalent of HBr, the addition product 1,2 is generated primarily at 40 ° C. When 1,3-butadiene reacts with HBr, a mixture of two products is obtained. One of them, 3-bromo-1-butene, is formed by the addition of HBr to one of the double bonds of the classic structure of this compound.
In contrast, the second and major product, 1-bromo-2-butene, does not have any of the terminal double bonds but contains a double bond between the C2-C3 carbons.
