Assign number 1 for least to 4 for most to indicate the relative basic strength of the following: (I) C6H5NH2 (II) p−NO2C6H4NH2 (III) m−NO2C6H4NH2 (IV) p−CH3OC6H4NH2
A
IIIIIIIV3124
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B
IIIIIIIV1234
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C
IIIIIIIV2341
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D
IIIIIIIV4132
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Solution
The correct option is AIIIIIIIV3124 Resonance effect will occur when the +R/-R group is present at para/ortho position. In (IV), −OCH3 is +R group which will increase the electron density on N by delocalistion of electron and make N more basic. Therefore, (IV) is most basic of all. In (II), −NO2 is -R group which will reduce the electron density on N by delocalistion of electron and make N less basic. Therefore, (II) is least basic of all. In (I), there is no +R/-R group, it is less basic than (IV). In (III), −NO2 is at meta position and -I effect operates so it pulls the electron density toward itself which will reduce the electron density on N and make it less basic but not as (II) because resonance effect dominates over inductive effect.