Keto - enol tautomerism is not shown by

Options

A. butan -2- one
B. 1 - phenylbutan -2- one
C. `p-O_(2)NC_(6)H_(4)CH_(2)COCH_(2)Ph`
D. `PhCOPh`

Answer

To determine which compound does not exhibit keto-enol tautomerism, we need to analyze the presence of alpha hydrogens in each of the given compounds. Keto-enol tautomerism occurs when a keto form (with a carbonyl group) can convert to an enol form (with a hydroxyl group adjacent to a double bond) through the movement of a hydrogen atom.

### Step-by-Step Solution:

1. **Identify the Compounds**: The question provides four compounds. We need to analyze each one for the presence of alpha hydrogens.

2. **Understanding Alpha Hydrogens**: Alpha hydrogens are the hydrogens attached to the carbon atom adjacent to the carbonyl carbon. For a compound to exhibit keto-enol tautomerism, it must have at least one alpha hydrogen.

3. **Analyze Each Compound**:
- **Compound A: Butane-2-one**:
- Structure: CH3-CO-CH2-CH3
- The carbonyl carbon (C=O) is the second carbon, and the adjacent carbons (first and third) have hydrogens. Therefore, it has alpha hydrogens and can undergo tautomerism.

- **Compound B: 1-Phenylbutane-2-one**:
- Structure: C6H5-CO-CH2-CH3
- The carbonyl carbon is again the second carbon, and the adjacent carbon has hydrogens. Thus, it also has alpha hydrogens and can undergo tautomerism.

- **Compound C: Para-nitrophenylacetone**:
- Structure: C6H4(NO2)-CH2-CO-CH3
- The carbonyl carbon is adjacent to a CH2 group, which has hydrogens. Hence, it has alpha hydrogens and can undergo tautomerism.

- **Compound D: Benzophenone (Ph-CO-Ph)**:
- Structure: C6H5-CO-C6H5
- Here, the carbonyl carbon is bonded to two phenyl groups, neither of which has any alpha hydrogens (no adjacent carbon with hydrogen). Therefore, it cannot undergo tautomerism.

4. **Conclusion**: Based on the analysis, the compound that does not show keto-enol tautomerism is **Benzophenone (Compound D)**.

### Final Answer:
The compound that does not exhibit keto-enol tautomerism is **Benzophenone (D)**.