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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o1230

The keto aldehyde shown has an aldehyde and a methyl ketone group. Select the correct statement(s) about its selective or complete reactions (an unhindered aldehyde is taken to be more electrophilic than a ketone).

  1. AOne equivalent of NaBH4 at low temperature preferentially reduces the aldehyde group
  2. BOne equivalent of CH3MgBr at low temperature preferentially adds to the aldehyde group
  3. COne equivalent of NaHSO3 preferentially forms the adduct at the ketone group
  4. DExcess LiAlH4 followed by work-up reduces both carbonyl groups, giving a diol

Answer: A, B, D

5-Oxohexanal contains an unhindered aldehyde and a more hindered, less electrophilic ketone, so a limited amount of NaBH4 or one equivalent of Grignard reagent at low temperature attacks the aldehyde preferentially. Excess lithium aluminium hydride reduces both groups to give hexane-1,5-diol. The statement that the ketone forms its bisulphite adduct preferentially is wrong, since aldehydes form bisulphite adducts more readily.
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