Question

Anti-Markovnikov's addition of HBr in the presence of peroxide is not observed in:

• A. propene
• B. 1-butene
• C. but-2-ene
• D. pent-2-ene

Answer 1

The correct option is C but-2-ene

In the presence of peroxide, addition of HBr to unsymmetrical alkenes takes place contrary to Markovnikov’s rule. In Markovnikov's rule, negative part of addendum (adding molecule) gets attached to that doubly bonded C which posses lower number of hydrogen atoms. Anti-Markovnikov's addition of HBr in the presence of peroxide is observed only with unsymmetrical alkenes. In option a, b, and d unsymmetrical alkenes are present.
$C{H}_{3}CH=C{H}_2$
(a)
$C{H}_2=CHC{H}_{2}C{H}_3$
(b)
$C{H}_{3}CH=CHC{H}_3$
(c)
$C{H}_{3}CH=CHC{H}_{2}C{H}_3$
(d)
Hence, the correct answer is option (c) as but-2-ene is a symmetrical alkene.