Which acid derivative is a functional isomer of carboxylic acids?

Options

A. Acid chlorides
B. Esters
C. Acid amides
D. Acid anhydrides

Answer

To determine which acid derivative is a functional isomer of carboxylic acids, we need to understand the concept of functional isomerism and analyze the options provided.

### Step-by-Step Solution:

1. **Understanding Functional Isomers**:
Functional isomers are compounds that have the same molecular formula but different functional groups. This means that while the number and types of atoms are the same, the arrangement and types of bonds differ.

2. **Identify the Molecular Formula of Carboxylic Acids**:
Carboxylic acids have the general formula \( RCOOH \) or \( C_nH_{2n+1}COOH \). For example, acetic acid (ethanoic acid) has the formula \( C_2H_4O_2 \).

3. **Analyzing the Options**:
- **Option 1: Acid Chloride (RCOCl)**:
The molecular formula would be \( C_nH_{2n+1}COCl \). This has a chlorine atom instead of a hydroxyl group, so it is not a functional isomer.
- **Option 2: Acid Anhydride (RCOOCOR)**:
The molecular formula would be \( C_{2n}H_{2n-2}O_3 \). This has two carbonyl groups and does not match the formula of a carboxylic acid, so it is not a functional isomer.
- **Option 3: Acid Amide (RCONH2)**:
The molecular formula would be \( C_nH_{2n+1}CONH2 \). This contains nitrogen and does not match the formula of a carboxylic acid, so it is not a functional isomer.
- **Option 4: Ester (RCOOR')**:
The molecular formula would be \( C_nH_{2n}O_2 \). Esters have the same molecular formula as carboxylic acids but differ in functional groups (ester vs. carboxylic acid).

4. **Conclusion**:
The only acid derivative that is a functional isomer of carboxylic acids is **Ester**. Therefore, the correct answer is **Ester**.