Question

The number of structural and configurational isomers of a bromo compound, `C_(5)H_(9)Br`, formed by the additionn of HBr to 2-penthyne respectively are
A. 1 and 2
B. 2 and 4
C. 4 and 2
D. 2 and 1

Answer 1

Correct Answer - B
Addition of HBr to 2-pentyne gives two structural isomers (I) and (II).
`CH_(3)-C-=C-CH_(2)CH_(3) overset(HBr) underset((I))(CH_(3)C(Br)=CHCH_(2)CH_(3))+underset((II))(CH_(3)CH=C(Br)CH_(2)CH_(3))`
Each one of these will exist as a pair of geometrical isomers as shown below:

thus, there are two structural and four configurational isomers.