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Explain the bromination of benzene with its mechanism. |
Answer» Solution :Addition of -Br group in place of H-atom of benzene is known as bromination. In bromination, Lewis acid `Febr_(3)` is used as catalyst and `Br_(2)` is used as reagent.  Fucntion of catalyst : In this reaction, `FeBr_(3)` is act as catalyst and combined with `Br_(2)`, form bromonium ion `(Br^(+))`.  Bromination reaction complete in two steps by electrophilic subtitution reaction which are as follows : (a) First slow steps : The stable `pi`-electron clouds of benzene is destructed by electrophilic bromonium ions, and attach with one carbon. One carbon converts into `sp^(3)` from `sp^(2)`. In this STEP energy is requried to break the bond and HENCE, this step is slower, and so addition of electrophilic `Br^(+)` ion can form stable `pi`-complex by RESONANCE.  Resonance structure of `pi`-complex is as follows : (A), (B), (C) and hybrid structure (D).  Proton liberated from the `sigma`-complex and form HBR, `FeBr_(3)` and bromobenzene. In bromobenzene H of benzene is substituted by Br ATOMS. "The mechanism of such bromination is of electrophilic substitution reaction". -Br of bromobenzene is of ortho and para directing and so in strong condition o-and p- dibromobenzene is formed. 
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