Question

When $3$-phenylpropene reacts with $ HBr $ in the presence of peroxide, the major product formed is

• A. $2$-bromo $1$-phenylpropane
• B. $1, 2$-dibromo $3$-phenylpropane
• C. $3$-($o$-bromophenyl) propene
• D. $1$-bromo-$3$-phenylpropane
• E. $3$-(p-bromophenyl) propene

Answer 1

Answer: (D)

In the presence of peroxides, the addition of $ HBr $ to unsymmetrical alkenes takes place contrary to Markownikoffs rule. This is known as peroxide effect or Kharasch effect.
$ \underset{3-phenylpropene}{\mathop{{{C}_{6}}{{H}_{5}}-C{{H}_{2}}-CH=C{{H}_{2}}}}\,+HBr\xrightarrow[Anti-Mark.addn.]{Peroxide} $
$ \underset{1-bromo-3-phenylpropene}{\mathop{{{C}_{6}}{{H}_{5}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}}}\,Br $