Write correct order of acidic strength of following compounds:
(a)`NO_(2) - CH_(2) - overset(O)overset(||)C - O - H `
`(b) F - CH_(2) - overset(O)overset(||)C - O - H `
`(c) Ph - CH_(2) - overset(O)overset(||)C - O - H `
(d) `CH_(3) - CH_(2) - overset(O)overset(||)C - O - H `

Answer

To determine the correct order of acidic strength of the given compounds, we need to analyze the stability of their conjugate bases after the removal of a proton (H⁺). The more stable the conjugate base, the stronger the acid.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- (a) `NO2 - CH2 - C(=O) - O - H`
- (b) `F - CH2 - C(=O) - O - H`
- (c) `Ph - CH2 - C(=O) - O - H`
- (d) `CH3 - CH2 - C(=O) - O - H`

2. **Form the Conjugate Bases:**
- For each compound, remove the acidic hydrogen (H⁺) to form the conjugate base.
- (a) Conjugate base: `NO2 - CH2 - C(=O) - O⁻`
- (b) Conjugate base: `F - CH2 - C(=O) - O⁻`
- (c) Conjugate base: `Ph - CH2 - C(=O) - O⁻`
- (d) Conjugate base: `CH3 - CH2 - C(=O) - O⁻`

3. **Analyze the Effects of Substituents:**
- The stability of the conjugate base is influenced by the presence of electron-withdrawing groups (EWGs) or electron-donating groups (EDGs).
- **(a) NO2**: A strong electron-withdrawing group, stabilizes the conjugate base by reducing electron density.
- **(b) F**: Also an electron-withdrawing group, but less effective than NO2.
- **(c) Ph (Phenyl)**: The phenyl group has a mild electron-withdrawing effect due to resonance but is not as strong as NO2 or F.
- **(d) CH3**: This is an electron-donating group (through +I effect), which destabilizes the conjugate base by increasing electron density.

4. **Rank the Stability of Conjugate Bases:**
- The order of stability based on the strength of the electron-withdrawing effect is:
- (a) `NO2` > (b) `F` > (c) `Ph` > (d) `CH3`
- Therefore, the order of acidic strength (stronger acids have more stable conjugate bases) will be:
- (a) > (b) > (c) > (d)

5. **Final Order of Acidic Strength:**
- The correct order of acidic strength is:
- **NO2 - CH2 - C(=O) - O - H > F - CH2 - C(=O) - O - H > Ph - CH2 - C(=O) - O - H > CH3 - CH2 - C(=O) - O - H**

### Summary:
The final order of acidic strength is:
**(a) > (b) > (c) > (d)**