Question

Anti markovnikov addition of hbr is not observed in which of following (a) propene (b) but-i-ene (c)but-2-ene (d) pent-2- Ene

Answer 1

antimarkonikov addition is not observed in option (a) propene ...!
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Answer 2

Answer: (c) but-2-ene

Explanation: Anti markonikov addition is addition of HBr to unsaturated compounds in which negative part $(Br^-)$ goes to the less substituted carbon of the double bond which contains and positive part $(H^+)$ of the reagent goes to more substituted carbon of the double bond.

a) propene

$CH_3CH=CH_2+HBr\xrightarrow[ ]{peroxide} CH_3CH_2CH_2Br$

b) but-1-ene

$CH_3CH_2CH=CH_2+HBr\xrightarrow[ ]{peroxide} CH_3CH_2CH_2CH_2Br$

c)  but-2-ene

$CH_3CH=CHCH_2+HBr\xrightarrow[ ]{peroxide}$ Both the carbons are similar and thus there is possibility of only one product.

d) pent-2- ene

$CH_3CH_2CH=CHCH_2+HBr\xrightarrow[ ]{peroxide} CH_3CH_2CH_2CHBrCH_3$