Question

The number of structural and configurational isomers of a bromo compound $C_5{H}_{9}Br$, formed by the addition of HBr to 2-pentyne respectively are :

• A. 1 and 2
• B. 2 and 4
• C. 4 and 2
• D. 2 and 1

Answer 1

The correct option is B 2 and 4

Addition of $HBr$ to $2$-pentyne gives two structural isomers I and II.

Each one of these will exist as a pair of geometrical isomers as shown.

Thus there are two structural and four configurational isomers.