The correct order of +M effect of ′N′ containing functional group on benzene ring, amongst the given compounds is
(I) (II) (III) (IV)
A
I>II>IV>III
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B
II>I>III>IV
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C
I>II>III>IV
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D
IV>III>II>I
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Solution
The correct option is CI>II>III>IV In (b), due to steric inhibition of resonance the amine group will goes out of the plane. Thus it will restrict the resonance of lone pair of electron of N on benzene ring. In (c), due to cross conjugation the lone pair of electron on N involves in delocalisation with carbonyl group. This decrease the +M effect of N. In (d), we have two carbonyl groups so more cross conjuation will exist and it results in least +M effect of N. In (a), due to absence of SIR and cross conjugate it will show the highest +M effect.