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Alcohols Phenols and Ethers question

2023 · 25 Jan · Shift 1 · Q11
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Alcohols Phenols and Ethers question

2023 · 25 Jan · Shift 1 · Q11

JEE MainChemistryAlcohols Phenols and EthersMCQ+4 / −1
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R : Assertion A : Acetal / Ketal is stable in basic medium. Reason R : The high leaving tendency of alkoxide ion gives the stability to acetal/ketal in basic medium. In the light of the above statements, choose the correct answer from the options given below :
  1. A
    A is false but R is true.
  2. B
    Both A and R are true but R is NOT the correct explanation of A
  3. C
    Both A and R are true and R is the correct explanation of A
  4. D
    A is true but R is false.
View written solutionFree

Correct answer: D

  1. Evaluate Assertion A

    Assertion: Acetal/Ketal is stable in basic medium.

    This is true.

    • Acetals and ketals are formed from aldehydes/ketones in acidic medium.
    • Their hydrolysis also occurs in acidic medium.
    • In basic medium, they are generally stable because base does not efficiently cleave the acetal/ketal linkage.

    So, Assertion A is true.

  2. Evaluate Reason R

    Reason: The high leaving tendency of alkoxide ion gives the stability to acetal/ketal in basic medium.

    This is false.

    • An alkoxide ion RO−RO^-RO− is a poor leaving group, not a good leaving group.
    • In basic medium, cleavage of acetal/ketal would require departure of an alkoxide ion, which is unfavorable.
    • This poor leaving-group ability is actually why acetals/ketals are stable in base.

    Therefore, the statement saying alkoxide has high leaving tendency is incorrect.

  3. Choose the correct option

    • Assertion A = True
    • Reason R = False

    Hence, the correct option is:

    D: A is true but R is false.

  4. Comparison with stored answer

    Stored correct answer: D

    Our derived answer matches the stored answer.

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