Question

Arrange the following in decreasing order of electrophilicity of carbonyl carbon.

• A. IV>I>III>II
• B. IV>I>II>III
• C. I>IV>III>II
• D. I>II>IV>III

Hint:

Carbonyl electrophilicity: aldehydes>ketones>carboxylic acids. Fewer alkyl groups and less resonance increase electrophilicity.

Answer 1

The Correct Option is A

To solve the problem, we need to arrange the given compounds in decreasing order of electrophilicity of their carbonyl carbon. Electrophilicity of the carbonyl carbon is influenced by the nature of substituents attached to the carbonyl group. Electron-withdrawing groups (like -COOH, -COCH₃) make the carbonyl carbon more electrophilic, while electron-donating groups (like -CH₃) decrease its electrophilicity.

1. Understanding the Concepts:

- Electrophilicity of Carbonyl Carbon: The more electron-withdrawing the substituent attached to the carbonyl group, the more electrophilic the carbonyl carbon is. Electron-withdrawing groups (such as -COOH and -COCH₃) increase electrophilicity by pulling electron density away from the carbonyl carbon, making it more susceptible to attack. On the other hand, electron-donating groups (such as -CH₃) decrease the electrophilicity of the carbonyl carbon.

2. Given Values:

The compounds are:

• I) Aldehyde (CHO)
• II) Carboxylic acid (COOH)
• III) Ester (COCH₃)
• IV) Aldehyde (CH₃CH₂CHO)

3. Analyzing the Electrophilicity:

1. IV) Aldehyde (CH₃CH₂CHO): The presence of an alkyl group (CH₃CH₂) makes the carbonyl carbon less electrophilic, but it is still more electrophilic than the carboxylic acid or ester due to fewer electron-withdrawing effects compared to the other groups.

2. I) Aldehyde (CHO): The absence of any electron-donating groups makes the carbonyl carbon highly electrophilic, but it is less electrophilic than the carboxylic acid.

3. III) Ester (COCH₃): The ester group is electron-withdrawing via resonance and inductive effects, but it is less electrophilic than the aldehyde due to the stabilizing effect of the alkoxy group.

4. II) Carboxylic acid (COOH): The carboxylic acid group is the most electron-withdrawing, making the carbonyl carbon the most electrophilic of all these compounds.

Final Answer:

The correct order of electrophilicity is IV>I>III>II (Option 1).