Find the number of structural and configurational isomers of a bromo compound `C_5H_9Br` formed by the addition of HBR to 2-pentyne.

Explanation

Addition of one molar proportion of HBr to `CH_3-CH_2-C-=C-CH_3` produces two structural isomers A and B .
`{:(" "CH_3CH_2-C-=C-CH_3),(" "darrHBr),(CH_3CH_2underset(Br(A))underset(|)C=CH-CH_3+CH_3-CH_2-CH=underset((B)Br)underset(|)C-CH_3):}`
Each of these strutural isomers can exist as a pair of geometrical isomers (cis and trans) and hence there are four possible configurational isomers.