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 structures of the compounds provided and identify the presence or absence of alpha hydrogen atoms. Here’s a step-by-step solution:

### Step 1: Understand Keto-Enol Tautomerism
Keto-enol tautomerism involves the interconversion between a keto form (with a carbonyl group, C=O) and an enol form (with a hydroxyl group, -OH, adjacent to a double bond). This process requires the presence of an alpha hydrogen atom, which is a hydrogen atom attached to the carbon adjacent to the carbonyl carbon.

### Step 2: Analyze the Given Compounds
We will analyze each of the given compounds to check for the presence of alpha hydrogen atoms.

1. **Butane-2-one (CH3-CO-CH2-CH3)**:
- Structure: CH3-C(=O)-CH2-CH3
- Alpha hydrogen: Yes, there are alpha hydrogens on the CH2 group adjacent to the carbonyl.

2. **1-Phenyl-2-butanone (C6H5-CO-CH2-CH3)**:
- Structure: C6H5-C(=O)-CH2-CH3
- Alpha hydrogen: Yes, there are alpha hydrogens on the CH2 group adjacent to the carbonyl.

3. **p-Nitrophenyl-2-butanone (C6H4(NO2)-CO-CH2-CH3)**:
- Structure: C6H4(NO2)-C(=O)-CH2-CH3
- Alpha hydrogen: Yes, there are alpha hydrogens on the CH2 group adjacent to the carbonyl.

4. **Benzophenone (C6H5-C(=O)-C6H5)**:
- Structure: C6H5-C(=O)-C6H5
- Alpha hydrogen: No, there are no alpha hydrogens because both adjacent carbons are part of phenyl rings.

### Step 3: Conclusion
Among the four compounds analyzed, **Benzophenone** does not have any alpha hydrogen atoms, and therefore it cannot exhibit keto-enol tautomerism.

### Final Answer
The compound that does not show keto-enol tautomerism is **Benzophenone**.

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