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What is mean by meta directing group ? Give examples of it and explain meta directing effect of -NO_(2). |
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Answer» Solution :(a) Definition : Due to presence of certain functional group on benzene ring if on second substitution of any functional group acquired meta POSITION in benzene then FIRST substituted benzene is known as meta directing group. (b) EXAMPLES : `-NO_(2), -COOH, -SO_(3)H, -CHO, -COOH_(3), -COCl, -COR, -COOR` etc are meta directing groups.  `-NO_(2)` group is present in nitrobenzene. This `-NO_(2)` group is meta directing. Following given structure (I) to (V) are resonating structures and (VI) is hybride structure.  In above given structure of nitrobenzene has positive charge of ortho and PARA position but meta poisiton is neutral. So more electro negative density is present on meta position. Therefore, postive charge electrophilic `-NO_(2)` group is attaches to meta position. So `-NO_(2)` is meta directing in nature. |
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