Which one of the following compounds does not show tautomerism ?

Options

A. `CH_3-CH_2-NO_2`
B. `CH_3-underset(CH_3)underset(|)overset(CH_3)overset(|)C-NO`
C. `CH_3-NH-overset(O)overset(||)C-CH_3`
D. `CH_3-overset(O)overset(||)C-underset(CH3)underset(|)(CH)-COOC_2H_5`

Answer

To determine which compound does not show tautomerism, we need to understand the concept of tautomerism and identify the compounds provided in the question. Tautomerism is a type of structural isomerism where compounds can readily interconvert between two forms, typically involving the relocation of a hydrogen atom and a double bond.

### Step-by-Step Solution:

1. **Understanding Tautomerism**:
- Tautomerism involves the shifting of a hydrogen atom and the movement of a double bond. The most common types of tautomerism are keto-enol tautomerism and imine-enamine tautomerism.

2. **Identifying the Compounds**:
- We need to analyze the compounds listed in the question to check if they have the ability to exhibit tautomerism.

3. **Analyzing Each Compound**:
- **Compound A**: If it has a carbonyl group (C=O) adjacent to a carbon with hydrogen (alpha position), it can show tautomerism.
- **Compound B**: If it has an imine (C=N) and an adjacent carbon with hydrogen, it can also show tautomerism.
- **Compound C**: If it has a structure like a carboxylic acid or an amide with an adjacent carbon that has hydrogen, it can show tautomerism.
- **Compound D**: If it has a nitrogen double bond (like N=O) and there is no hydrogen on the alpha carbon, it cannot show tautomerism.

4. **Conclusion**:
- After analyzing the compounds, we find that **Compound D**, which has a nitrogen double bond and lacks an alpha hydrogen, does not exhibit tautomerism.

### Final Answer:
The compound that does not show tautomerism is **Compound D**.