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JEE Advanced levelSingle correct optionDifficulty 3 of 3g1245

The compound shown has a dipole moment much larger than that of a saturated cyclic ketone of similar size. The best explanation is

  1. Aa dipolar contributor with a 6 pi electron aromatic tropylium ring and a negative oxygen contributes strongly
  2. Bthe ring is antiaromatic with 8 pi electrons
  3. Cthe ring carbons are sp3 hybridised
  4. Dthe carbonyl carbon is not part of the ring pi system

Answer: A

The compound shown is tropone. The C=O group is polarised so that carbon is positive and oxygen is negative. The dipolar contributor has a tropylium ring with 6 pi electrons, so it is aromatic and contributes strongly. This enhances the charge separation.
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