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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ap231

The cyclic diol shown is heated with dilute acid to give a single carbonyl product by loss of one molecule of water. Choose all correct statements about the product.

  1. AIts molecular formula is .
  2. BOne of the two five-membered rings is enlarged to a six-membered ring.
  3. CIt is a spiro ketone containing a quaternary carbon common to both rings.
  4. DIt is an aldehyde formed by a hydride shift.

Answer: A, B, C

The diol is 1,1'-bi(cyclopentyl)-1,1'-diol (). Loss of water and migration of a ring expands one ring to six members and gives spiro[4.5]decan-6-one, , whose spiro carbon is quaternary. No hydrogen is available on either carbinol carbon, so no aldehyde forms and D is wrong.
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