The correct order of acid strength of the following compounds:

Options

A. Phenol
B. p-Cresol
C. m-Nitrophenol
D. p-Nitrophenol

Answer

To determine the correct order of acid strength of the given compounds, we will analyze the structures and the effects of substituents on the acidity. The compounds are:

1. A: Phenol (C6H5OH)
2. B: p-Nitrophenol (C6H4(NO2)OH)
3. C: m-Nitrophenol (C6H4(NO2)OH)
4. D: p-Cresol (C6H4(CH3)OH)

### Step-by-Step Solution:

**Step 1: Identify the compounds and their substituents.**
- A: Phenol (no substituents)
- B: p-Nitrophenol (nitro group at para position)
- C: m-Nitrophenol (nitro group at meta position)
- D: p-Cresol (methyl group at para position)

**Step 2: Analyze the effects of substituents on acidity.**
- Electron-withdrawing groups (EWGs) increase acidity by stabilizing the negative charge on the conjugate base.
- Electron-donating groups (EDGs) decrease acidity by destabilizing the negative charge on the conjugate base.

**Step 3: Determine the impact of substituents on each compound.**
- **p-Nitrophenol (B)**: The nitro group is an EWG and is in the para position, which allows for resonance stabilization of the conjugate base. This makes B the strongest acid.
- **m-Nitrophenol (C)**: The nitro group is still an EWG but is in the meta position, which does not allow for resonance stabilization of the conjugate base. Thus, C is less acidic than B.
- **Phenol (A)**: Phenol has no substituents that can stabilize or destabilize the conjugate base significantly, so its acidity is moderate.
- **p-Cresol (D)**: The methyl group is an EDG and decreases acidity. Therefore, D is the least acidic.

**Step 4: Rank the compounds based on acidity.**
- The order of acidity from strongest to weakest is:
1. p-Nitrophenol (B) - strongest
2. m-Nitrophenol (C)
3. Phenol (A)
4. p-Cresol (D) - weakest

### Final Order of Acid Strength:
B > C > A > D