The number of structural and configurational isomers of a bromo compound, `C_5H_9Br`, formed by the addition of `HBr` to 2-pentyne respectively, is:

Options

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

Answer

B

Explanation

When HBr adds on 2-pentyne it gives two structural isomers i.e. (I) and (II).
`CH_3-C-=C-CH_2-CH_3 overset(HBr)(to)`
`underset(I)(CH_3-oversetunderset(|)(Br)(C ) = CHCH_2CH_3) + underset(II)(CH_3CH=oversetunderset(|)(Br)(C )-CH_2-CH_3)`
Each one of these (i.e. I and II) exists as a pair of geometrical isomers (cis and trans). Thus we have two structural and four configurational isomers.