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JEE Main levelSingle correct optionDifficulty 2 of 3g1229

The pi system of the compound shown is best described as

  1. Alinearly conjugated through all four carbons
  2. Bcross-conjugated
  3. Cisolated
  4. Dcumulated

Answer: B

The compound shown is divinyl ketone (penta-1,4-dien-3-one). Each C=C is conjugated with the C=O, but the two C=C bonds are not conjugated with each other through the carbonyl carbon. This is cross-conjugation.
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