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Question
Which of the following is the correct order of electron density on the benzene ring in the following compounds?
Which of the following is the correct order of electron density on the benzene ring in the following compounds?
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Solution
The correct option is A I>II>III
In case of Halogens, I effect dominates over M effect. Hence they are electron-withdrawing in nature. The overall withdrawing power of Cl is more than F when attached to conjugated system even though F is more electronegative.
−Cl has three effects +M,−M,−I . In case of −Cl, +M weakens up due to 2p−3p overlapping (leading to pi bond). But it is not so in case of −F which involve to 2p−2p overlap which is more effective. So, +M effect of −F is more than −Cl.
Therefore, the correct order of electron density is:
I>II>III
In case of Halogens, I effect dominates over M effect. Hence they are electron-withdrawing in nature. The overall withdrawing power of Cl is more than F when attached to conjugated system even though F is more electronegative.
−Cl has three effects +M,−M,−I . In case of −Cl, +M weakens up due to 2p−3p overlapping (leading to pi bond). But it is not so in case of −F which involve to 2p−2p overlap which is more effective. So, +M effect of −F is more than −Cl.
Therefore, the correct order of electron density is:
I>II>III
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2
(II)
(III) 
(IV) 
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