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JEE Main levelSingle correct optionDifficulty 2 of 3g1038

The dipole moment of chlorobenzene (about 1.6 D) is smaller than that of chlorocyclohexane (about 2.2 D). The main electronic reason is that in chlorobenzene

  1. Athe lone pair on Cl is delocalised into the ring (+M), opposing the -I shift of electrons toward Cl
  2. BCl has no lone pair that can be donated
  3. Cthe C-Cl bond is much longer than in chlorocyclohexane
  4. Dthe benzene ring exerts a strong +I effect that pushes electrons toward Cl

Answer: A

Cl withdraws sigma electrons by -I but donates a lone pair into the ring by +M. The +M effect acts in the opposite direction to the -I effect and reduces the net polarity of the C-Cl bond, lowering the dipole moment relative to chlorocyclohexane where only -I operates.
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