Arrange the following amides according to their relative reactivity when reacted with Br2 in excess of strong base:
A
IV > I > II > III
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B
II > I > III > IV
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C
II > IV > III > I
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D
II > I > IV > III
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Solution
The correct option is D II > I > IV > III In Hoffmann bromamide reaction, a nitrene is formed in the intermediate step which then rearrange into isocyanate.
Donating nature of R group increase the rate. If R has more electron density, it will migrate more readily and hence increase the rate. Methyl group increase the electron density into the ring and will react with fastest rate. NO2 is strong electron withdrawing group than Cl. So it will reduce the electron density in the ring and react with least rate. Hence the order for the given species will be: II>I>IV>III