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Arrange the following set of compounds in order of their decreasing relative reactivity with an electrophile, E^+. (a)Chlorobenzene, 2,4-dinitrochlorobenzene, p-nitrochlorobenzene. (b)Toluene, p-H_3C-C_6H_4-NO_2, p-O_2N-C_6H_4-NO_2 |
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Answer» Solution :The typical reactions of benzene are electrophilic substitution reactions. Higher the electron-density in the benzene ring , more reactive is the COMPOUND towards these reactions. Since, `NO_2` is a more POWERFUL electron-withdrawing group than Cl, therefore, more the number of NITRO groups, less reactive is the compound . THUS, the overall reactivity decreases in the order : Chlorobenzene gt p-nitrochlorobenzene gt 2,4-dinitrochlorobenzene. (b)Here, `CH_3` group is electron DONATING but `NO_2` group is electron-withdrawing. Therefore, the maximum electron-density will be in the toluene, followed by p-nitrotoluene followed by p-dinitrobenzene . Thus, overall reactivity decreases in the order : Toluene gt `p-H_3C - C_6H_4-NO_2 gt p-O_2N - C_6H_4-NO_2` |
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