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

The given question requests an analysis of an assertion and its corresponding reason with respect to the stability of acetals and ketals in different media.

1. Understanding the Assertion: The assertion is that acetals and ketals are stable in basic medium. This statement is correct because acetals and ketals, formed by the reaction of aldehydes or ketones with alcohols in the presence of an acid catalyst, tend to be stable in basic media. The stability arises because bases do not provide the necessary acidity to catalyze their cleavage back into their corresponding aldehydes or ketones and alcohols.
2. Understanding the Reason: The provided reason is that the high leaving tendency of the alkoxide ion gives stability to the acetal/ketal in a basic medium. This statement is incorrect. In reality, the stability in a basic medium is due to the absence of acidic hydrogen ions which are necessary for the breakdown of acetal/ketal back into their reactants. Alkoxide ions are not better leaving groups, and thus, their presence does not contribute to stability.
3. Evaluating the Relationship: While the assertion is true, the reason given is not the correct explanation of the assertion. Therefore, the assertion does not logically stem from or correlate with the given reason.
4. Selecting the Correct Option: Based on the analysis above, the correct choice is: A is true but R is false.

This reasoning acknowledges that although acetals and ketals are naturally stable in basic environments, the reason does not appropriately explain this stability.