Question

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 :

• A. Both $A$ and $R$ are true but $R$ is NOT the correct explanation of $A$
• B. A is false but $R$ is true
• C. A is true but $R$ is false
• D. Both $A$ and $R$ are true and $R$ is the correct explanation of $A$

Answer 1

The Correct Option is C

To solve the given problem, let's analyze the assertion and the reason separately:

1. Assertion A: Acetals/Ketals are stable in basic medium.
2. Reason R: The high leaving tendency of alkoxide ion gives the stability to acetal/ketal in basic medium.

Firstly, acetals and ketals are derivatives of alcohols formed by the reaction of carbonyl compounds (aldehydes or ketones) with alcohols. They are used to protect carbonyl groups in organic synthesis.

• Acetals and ketals are stable in the presence of bases because bases do not provide the protons (H⁺) necessary to hydrolyze them back to carbonyl compounds and alcohols.
• In contrast, acetals and ketals are easily hydrolyzed in acidic conditions, where the presence of excess H⁺ ions facilitates the cleavage of the acetal/ketal to return to the original carbonyl compound.

Therefore, Assertion A is true: Acetal/Ketal is indeed stable in basic medium.

Now, let's evaluate the reason:

• Alkoxide ions (RO^-) are good leaving groups in the presence of a strong acid that can protonate them to form a better leaving group (ROH), but not in neutral or basic solutions.
• In a basic medium, acidic protons are absent, so the hydrolysis reaction (which would depend on the leaving group ability of the alkoxide) does not proceed.
• Therefore, the stability of acetals/ketals in a basic medium is not due to the "leaving tendency" of alkoxide ions.

Reason R is false: The high leaving tendency of alkoxide ion is not relevant in explaining the stability of acetals and ketals in a basic medium.

Based on this analysis, the correct answer is: A is true but R is false.