Which of the following compounds cannot exhibit metamer-ism?

Options

A. Ether
B. Carboxylic acid
C. Ester
D. ketone

Explanation

To determine which of the given compounds cannot exhibit metamerism, we need to understand the concept of metamerism and the conditions required for it to occur.

### Step-by-Step Solution:

1. **Understanding Metamerism**:
Metamerism is a type of isomerism that occurs in compounds with the same molecular formula but different structural arrangements of atoms, particularly due to the presence of a bivalent or polyvalent functional group.

2. **Identifying the Necessary Condition**:
For metamerism to occur, the compound must have a bivalent (or polyvalent) group. This means that the compound must have at least two functional groups that can be varied while keeping the rest of the structure the same.

3. **Analyzing the Given Compounds**:
- **Option A**: Alkyl amine (R-NH-R') - This compound has a bivalent nitrogen atom, allowing for metamerism.
- **Option B**: Ether (R-O-R') - This compound also has a bivalent oxygen atom, allowing for metamerism.
- **Option C**: Carboxylic acid (RCOOH) - This compound is monovalent because the carboxylic acid group (-COOH) does not allow for variation on both sides of the functional group. Therefore, it cannot exhibit metamerism.
- **Option D**: Ketone (RCO-R') - This compound has a bivalent carbonyl group, allowing for metamerism.

4. **Conclusion**:
Based on the analysis, the compound that cannot exhibit metamerism is **Option C: Carboxylic acid (RCOOH)**, as it is a monovalent compound.

### Final Answer:
**Carboxylic acid (RCOOH) cannot exhibit metamerism.**

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