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JEE · NEET Previous Year Question

Given below are two statements:
Statement I: Cross aldol condensation between two different aldehydes will always produce four different products.
Statement II: When semicarbazide reacts with a mixture of benzaldehyde and acetophenone under optimum pH , it forms a condensation product with acetophenone only.
In the light of the above statements, choose the correct answer from the options given below

Topic: JEE PYQ

Answer: B. Full step-by-step solution below.

  1. AStatement I is false but Statement II is true
  2. BBoth Statement I and Statement II are false
  3. CBoth Statement I and Statement II are true
  4. DStatement I is true but Statement II is false

Correct answer: B

Solution

(b) Statement I: Cross aldol condensation between two different aldehydes produces four products only if both aldehydes have -hydrogen atoms. If one aldehyde lacks -hydrogen (e.g., benzaldehyde and acetaldehyde), only two products are typically formed (one self and one cross). If neither has -hydrogen, no aldol condensation occurs. Thus, it does not 'always' produce four products. Statement I is false.
Statement II: Benzaldehyde is an aldehyde and acetophenone is a ketone. Aldehydes are generally more reactive than ketones towards nucleophilic addition reactions due to less steric hindrance and greater electronic deficiency of the carbonyl carbon. Therefore, semicarbazide will react faster with benzaldehyde than with acetophenone. The statement claiming it forms a product with acetophenone only is incorrect. Statement II is false.

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