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MCAT Organic Chemistry – Ketones

  • by Kerry Goldstein
  • Feb 26, 2015
  • MCAT Blog, MCAT Organic, MCAT Question of the Day

Which of the following is true concerning the reduction of a ketone?

A) If carried out using NaBH4, it will result in the formation of a tertiary alcohol.
B) It cannot be accomplished using LiAlH4 without first hydrolyzing the ketone.
C) If carried out using LiAlH4 and workup in acid, it will result in the formation of a secondary alcohol.
D) One equivalent of alcohol will convert the starting product to a hemiacetal and two equivalents will convert it to an acetal.

Explanation

A) If carried out using NaBH4, it will result in the formation of a tertiary alcohol.
B) It cannot be accomplished using LiAlH4 without first hydrolyzing the ketone.
C) If carried out using LiAlH4 and workup in acid, it will result in the formation of a secondary alcohol.
D) One equivalent of alcohol will convert the starting product to a hemiacetal and two equivalents will convert it to an acetal.

A ketone is an oxygen double-bonded to a secondary carbon. When the ketone is reduced to an alcohol (most commonly with NaBH4 or LiAlH4), a secondary alcohol is thus formed, making (C) the right answer.

A: The carbonyl carbon of a ketone is only bonded to two other carbons, thus it is not form a tertiary group.

B: Reducing a ketone can be accomplished with either NaBH4 or LiAlH4 and does not require an prior steps.

D: Ketones can be converted to ketals, not acetals. Aldehydes can be converted to acetals.

 

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