Which `H` atom in the following ester is most acidic ?
`overset(1)(CH_(3))-overset(2)(CH_(2))-overset(O)overset(||)(C)-overset(3)(CH_(2))-overset(O)overset(||)(C)-O-overset(4)(CH_(2))overset(5)(CH_(3))`

Options

A. 1
B. 2
C. 3
D. 4

Explanation

To determine which hydrogen atom in the given ester is the most acidic, we need to analyze the structure and the effects of the surrounding groups on the acidity of the hydrogen atoms.

### Step-by-Step Solution:

1. **Identify the Structure**: The ester can be represented as follows:
- `CH3-CH2-C(=O)-CH2-C(=O)-O-CH2-CH3`
- Here, we have five hydrogen atoms on different carbon atoms.

2. **Understand Acidity**: The acidity of a hydrogen atom is influenced by the presence of electron-withdrawing groups (EWGs) and electron-donating groups (EDGs). EWGs increase acidity by stabilizing the negative charge on the conjugate base formed after deprotonation, while EDGs decrease acidity.

3. **Analyze Each Hydrogen**:
- **Hydrogens on Carbon 1 (`CH3`)**: These hydrogens are affected by the +I effect of the adjacent methyl group, which decreases acidity.
- **Hydrogens on Carbon 2 (`CH2`)**: These hydrogens experience a +I effect from the adjacent methyl group and a -I effect from the carbonyl group, resulting in a moderate acidity.
- **Hydrogens on Carbon 3 (`CH2` adjacent to `C=O`)**: These hydrogens are influenced by the -I effect from the carbonyl group on both sides, which increases acidity significantly.
- **Hydrogens on Carbon 4 (`CH2`)**: These hydrogens are influenced by -I from the carbonyl group on one side and +I from the adjacent carbon chain, leading to lower acidity.
- **Hydrogens on Carbon 5 (`CH3`)**: Similar to Carbon 1, these hydrogens are influenced by the +I effect from the adjacent carbon chain, decreasing acidity.

4. **Determine the Most Acidic Hydrogen**:
- The hydrogen on Carbon 3 is the most acidic because it is surrounded by two electron-withdrawing carbonyl groups (C=O), which exert a -I effect on both sides. This stabilizes the negative charge on the conjugate base formed after deprotonation, making it more acidic than the other hydrogens.

5. **Conclusion**: The most acidic hydrogen in the given ester is the hydrogen on Carbon 3.

### Final Answer:
The most acidic hydrogen atom in the given ester is from Carbon 3.

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