Identify the compound that exhibits tautomerism.

Options

A. 2-Butene
B. Lactic acid
C. 2-Pentanone
D. Phenol

Answer

To identify the compound that exhibits tautomerism, we will analyze the given options step by step. Tautomerism is a chemical phenomenon where a compound exists in two interconvertible forms, typically involving the migration of a hydrogen atom and a change in the position of a double bond.

### Step-by-Step Solution:

1. **Understanding Tautomerism**:
- Tautomerism involves the migration of a hydrogen atom and a shift in the position of a double bond. This often occurs between keto and enol forms.

2. **Analyzing the Options**:
- We need to evaluate each compound provided in the options (let's assume they are A, B, C, and D) to see if they can undergo tautomerism.

3. **Option A: But-2-ene**:
- Structure: CH3-CH=CH-CH3
- Analysis: This compound is an alkene and does not have a functional group that can participate in tautomerism. There is no hydrogen migration possible here.
- Conclusion: **Does not exhibit tautomerism.**

4. **Option B: Lactic Acid**:
- Structure: CH3-CHOH-COOH
- Analysis: Lactic acid has a hydroxyl group and a carboxylic acid. However, the migration of hydrogen does not lead to a stable tautomer. Thus, it does not exhibit tautomerism.
- Conclusion: **Does not exhibit tautomerism.**

5. **Option C: 2-Pentanone**:
- Structure: CH3-CO-CH2-CH2-CH3
- Analysis: This is a ketone. The hydrogen from the alpha carbon can migrate to the oxygen, forming an enol. This migration leads to the formation of a double bond between the alpha carbon and the carbonyl carbon.
- Conclusion: **Exhibits tautomerism.**

6. **Option D: Phenol**:
- Structure: C6H5OH
- Analysis: While phenol has a hydroxyl group, it is aromatic and does not easily undergo tautomerism. The stability of the aromatic system prevents the migration of hydrogen.
- Conclusion: **Does not exhibit tautomerism.**

7. **Final Conclusion**:
- Among the options analyzed, **2-Pentanone (Option C)** is the compound that exhibits tautomerism.