question_answer

In the reaction of\[C{{H}_{2}}=C{{H}_{2}}\]and HBr initial addition occurs of:

A)  indefinite

B)  \[{{H}^{+}}+B{{r}^{-}}\]both at one time

C)  \[{{H}^{+}}\]

D) \[B{{r}^{-}}\]

Correct Answer: C

Solution :

 Key Idea: Alkene undergo electrophilic addition reaction. Electrophile is electron deficient species. During electrophilic addition electrophile first adds across \[C=C\]or \[C=C.\] (i) \[C{{\overset{+}{\mathop{H}}\,}_{2}}-CH_{2}^{-}+{{H}^{+}}+B{{r}^{-}}\] (ii) \[CH_{2}^{+}-CH_{2}^{-}+{{H}^{+}}\xrightarrow{{}}CH_{2}^{+}-C{{H}_{3}}\] (iii) \[CH_{2}^{+}-C{{H}_{3}}+B{{r}^{-}}\xrightarrow{{}}C{{H}_{2}}Br-C{{H}_{3}}\] \[\therefore \]Initial addition occur by \[{{H}^{+}}.\]