Question

Directions: Each question contains Statement- 1 and Statement- 2 and has the following choices (a), (b), (c) and (d), out of which ONLY ONE is correct. (a) Statement- 1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement- 1 (b) Statement- 1 is True, Statement- 2 is True; Statement- 2 is NOT a correct explanation for Statement- 1 (c) Statement- 1 is True, Statement- 2 is False (d) Statement- 1 is False, Statement- 2 is True Statement 1 Acetals and ketals are unstable in aqueous acid conditions, but quite stable to alkaline conditions. and Statement 2 A weaker base like (OH) cannot displace a stronger base like (OR) found in acetals and ketals.

Short answer

Answer: Yes, Statement 2 is a correct explanation for Statement 1. Acetals and ketals are more stable under alkaline conditions because a weaker base like (OH) cannot displace a stronger base like (OR) found in acetals and ketals.

Step-by-step solution

Analyze Statement 1

Let's first analyze Statement 1: Acetals and ketals are unstable in aqueous acid conditions, but quite stable to alkaline conditions. This statement is True. Acetals and ketals are formed from the reaction between an aldehyde or ketone with an alcohol in the presence of an acid catalyst, and they can easily hydrolyze back to their respective aldehyde/ketone and alcohol under acidic conditions. However, they are more stable under alkaline conditions because the hydrolysis reaction does not readily occur.

Analyze Statement 2

Now let's analyze Statement 2: A weaker base like (OH) cannot displace a stronger base like (OR) found in acetals and ketals. This statement is True as well. In the general sense, a stronger base displaces a weaker base in a reaction. In this case, the alkoxide ion (OR) is a stronger base than the hydroxide ion (OH). When we consider the equilibrium between the reactants and products, the less stable hydroxide ion (OH) does not notably favor the formation of acetals or ketals.

Evaluate the relationship between Statement 1 and Statement 2

Now, let's decide if Statement 2 is a correct explanation for Statement 1. Statement 2 explains why acetals and ketals are more stable in alkaline conditions (due to the weaker base OH not being able to displace OR). Therefore, Statement 2 is a correct explanation for Statement 1.

Choose the correct answer

Based on the analysis, Statement 1 is True, Statement 2 is True, and Statement 2 is a correct explanation for Statement 1. So, the correct answer is (a) Statement- 1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement- 1.

Key concepts

Aqueous acid conditions

In aqueous acid conditions, acetals and ketals show low stability. Acetals and ketals are typically created through a reaction involving an aldehyde or a ketone and an alcohol, catalyzed by an acid. This reaction forms an acetal or ketal and water. However, the presence of excess water and an acid can actually reverse this process, breaking the acetal or ketal back down into the starting aldehyde or ketone and the alcohol.

This reversal process is known as hydrolysis, and it’s facilitated by the acidic conditions which provide an environment for the reaction to proceed easily. The acidic conditions protonate the acetal or ketal, making it susceptible to nucleophilic attack by water, which then leads to bond cleavage. For students, it's key to understand that the stability of these compounds is greatly reduced in the presence of an acid, due to this reverse reaction.

Alkaline conditions

Under alkaline conditions, acetals and ketals exhibit significant stability. Alkaline conditions are the opposite of acidic ones, characterized by a higher pH and the presence of hydroxide ions (OH).

These conditions do not favor the hydrolysis of acetals and ketals. The lack of acidic protons means there is no protonation of acetals and ketals, which is a necessary step for hydrolysis in acid. Without this step, water molecules cannot effectively attack and cleave the bonds within acetals and ketals, preserving their stability. Additionally, in a basic environment, any reactions would favor removal of protons rather than attack of nucleophiles, hindering the breakdown of acetals and ketals.

Base displacement

The displacement of one base by another in chemical reactions involves several factors, including the relative strength of the bases involved. In the context of acetals and ketals, this concept is based on the principle that a weaker base cannot displace a stronger base.

The hydroxide ion (OH) is a weaker base compared to the alkoxide ion (OR), commonly found in acetals and ketals. Bases are often compared by their ability to donate electron pairs. Alkoxide ions have stronger electron-donating ability due to their lower electronegativity compared to hydroxide ions. Thus, in a reaction setting, the stronger alkoxide base remains in place, and the weaker hydroxide base cannot effectively compete or displace it. This principle underlies the stability of acetals and ketals in various chemical environments, particularly under suiting alkaline conditions where hydrolysis is not promoted.