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Aldehydes Ketones and Carboxylic Acids question

2021 · 1 Sep · Shift 2 · Q10
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Aldehydes Ketones and Carboxylic Acids question

2021 · 1 Sep · Shift 2 · Q10

JEE MainChemistryAldehydes Ketones and Carboxylic AcidsMCQ+4 / −1
Given below are two statements : Statement I : The nucleophilic addition of sodium hydrogen sulphite to an aldehyde or a ketone involves proton transfer to form a stable ion. Statement II : The nucleophilic addition of hydrogen cyanide to an aldehyde or a ketone yields amine as final product. In the light of the above statements, choose the most appropriate answer from the options given below :
  1. A
    Both Statement I and Statement are true.
  2. B
    Statement I is true but Statement II is false.
  3. C
    Statement I is false but Statement II is true.
  4. D
    Both Statement I and Statement II are false.
View written solutionFree

Correct answer: B

  1. Analyze Statement I

    In the nucleophilic addition of sodium hydrogen sulphite, the nucleophile is bisulphite ion, \ceHSO3−\ce{HSO3^-}\ceHSO3−.

    For an aldehyde or ketone, the reaction proceeds as: \ceR2C=O+HSO3−−>R2C(OH)SO3−\ce{R2C=O + HSO3^- -> R2C(OH)SO3^-}\ceR2C=O+HSO3−−>R2C(OH)SO3−

    Mechanism:

    • \ceHSO3−\ce{HSO3^-}\ceHSO3− attacks the electrophilic carbonyl carbon.
    • A tetrahedral alkoxide intermediate is formed.
    • Then proton transfer occurs, giving the bisulphite addition product, which is a stable ionic compound.

    Hence, Statement I is true.

  2. Analyze Statement II

    Addition of hydrogen cyanide to an aldehyde or ketone gives a cyanohydrin, not an amine.

    General reaction: \ceR2C=O+HCN−>R2C(OH)CN\ce{R2C=O + HCN -> R2C(OH)CN}\ceR2C=O+HCN−>R2C(OH)CN

    The product contains both:

    • \ce−OH\ce{-OH}\ce−OH group
    • \ce−CN\ce{-CN}\ce−CN group

    This product is called a cyanohydrin.

    An amine is not the direct final product of this nucleophilic addition.

    Hence, Statement II is false.

  3. Evaluate options

    • A: Both true →\rightarrow→ Incorrect
    • B: Statement I true, Statement II false →\rightarrow→ Correct
    • C: Statement I false, Statement II true →\rightarrow→ Incorrect
    • D: Both false →\rightarrow→ Incorrect

  4. Final Answer

    The correct option is: B\boxed{\text{B}}B​

  5. Comparison with stored correct answer

    Stored correct answer = B

    My derived answer = B

    Therefore, they agree.

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