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 Eventhough carboxylic acids contain a \(>C=O\) group, they do not give the characteristic reaction of carbonyl compounds. and Statement 2 The electrophilicity of carbonyl carbon is less in carboxylic acids due to resonance.

Short answer

Answer: Carboxylic acids do not give the characteristic reactions of carbonyl compounds due to the reduced electrophilicity of the carbonyl carbon, which is caused by resonance stabilization involving the hydroxyl group.

Step-by-step solution

Statement 1:

Eventhough carboxylic acids contain a \(>C=O\) group, they do not give the characteristic reaction of carbonyl compounds. This statement is True. A carboxylic acid contains a carbonyl (\(C=O\)) group and a hydroxyl (\(-OH\)) group bonded to the same carbon atom. Although it has the carbonyl group, it exhibits different reactions than simple carbonyl compounds, such as aldehydes and ketones. Carboxylic acids typically undergo reactions like esterification, reduction, and acid-base reactions, while aldehydes and ketones mainly undergo nucleophilic addition reactions.

Statement 2:

The electrophilicity of carbonyl carbon is less in carboxylic acids due to resonance. This statement is also True. In carboxylic acids, the carbonyl carbon is less electrophilic than in aldehydes or ketones due to resonance stabilization. The lone pair of electrons on the oxygen atom of the hydroxyl group can delocalize into the carbonyl group's pi bond, forming a resonance structure where the negative charge is distributed between both oxygen atoms. This delocalization stabilizes the molecule and makes the carbonyl carbon less electrophilic and less prone to nucleophilic addition reactions. Now, let's examine the relationship between these two statements.

Relationship between Statement 1 and Statement 2:

Statement 2 is a correct explanation for Statement 1. The reason why carboxylic acids do not give the characteristic reactions of carbonyl compounds is due to the reduced electrophilicity of the carbonyl carbon. This reduced electrophilicity is caused by resonance, as explained in Statement 2. Since both statements are true and Statement 2 is a correct explanation for Statement 1, the correct answer to this exercise is: (a) Statement- 1 is True, Statement- 2 is True; Statement- 2 is a correct explanation for Statement- 1.

Key concepts

carbonyl compounds

Carbonyl compounds are organic molecules that feature a carbon-oxygen double bond (\( >C=O \)). This functional group is quite essential in organic chemistry, appearing in a variety of molecules like ketones, aldehydes, carboxylic acids, and more. The carbon atom in this group is typically sp² hybridized, forming a planar structure.

The reactions of carbonyl compounds are primarily determined by the polarity of the \( C=O \) bond. The carbon atom carries a partial positive charge, making it an attractive site for nucleophiles (electron pair donors). Popular reactions include nucleophilic addition. It's important to note that the behavior of carbonyl compounds can vary significantly based on additional functional groups attached to the carbonyl carbon. In carboxylic acids, this behavior is modified due to the presence of the hydroxyl group (-OH).

electrophilicity

Electrophilicity refers to an atom's ability to attract electrons towards itself. In carbonyl groups, electrophilicity is an important property since it influences how the compound reacts. The carbon in the \( C=O \) bond of carbonyl compounds is often electrophilic due to its partial positive charge.

However, in carboxylic acids, the presence of a hydroxyl group affects this electrophilicity. The oxygen in the hydroxyl group possesses lone pairs, which participate in resonance, reducing the positive charge on the carbonyl carbon. This makes the carbon less attractive to nucleophiles.

• The carbonyl carbon in aldehydes and ketones directly participates in nucleophilic additions.
• In carboxylic acids, the reduced electrophilicity means they typically undergo alternative reactions like esterification.

This variation in electrophilicity explains why different carbonyl compounds exhibit different chemical behaviors.

resonance stabilization

Resonance stabilization is a key concept in understanding the chemical stability of a molecule. It involves the distribution of electrons across multiple atoms, allowing a molecule to stabilize negative charges more effectively. In the context of carboxylic acids, resonance plays a vital role.

The carboxylic acid group consists of both the carbonyl \((> C=O)\) and the hydroxyl groups (-OH). Through resonance, the lone pairs on the hydroxyl oxygen can delocalize into the carbonyl’s pi bond. This forms a resonance structure where the negative charge is shared across both oxygen atoms and not just localized on one.

• This delocalization leads to greater stability of the carboxylic acid molecule, compared to ketones and aldehydes.
• It also reduces the electrophilicity of the carbonyl carbon, impacting its reactivity.

Ultimately, resonance stabilization in carboxylic acids prevents typical carbonyl reactions like nucleophilic addition, favoring other types of reactions instead.