Write the names and structures of the two alkenes (molecular formula:`C_4H_8`) which give the same compound when added to HBr in the absence of organic peroxide but different compounds when added to HBr in the presence of peroxide.

Explanation

When but-1-ene `(CH_3CH_2CH=CH_2)` and but-2-ene `(CH_3CH=CHCH_3)` react with HBr in absence of an organic peroxide, the same product is obtained.

However, in presence of an organic peroxide, addition of HBr to but-1-ene occurs contrary to the Markownikoff's rule and hence different products are obtained in these two cases.

`underset("But-2-ene")(CH_3CH=CHCH_3+HBr)overset("Organic peroxide")tounderset("2-bromobutane")(CH_3CH_2CHBrCH_3)`