Which one of the following compounds is most acidic

Options

A. `Cl-CH_(2)-CH_(2)-OH`
B.
C.
D.

Answer

To determine which compound is the most acidic among the given options, we can follow these steps:

### Step 1: Identify the Compounds
We have one aliphatic alcohol and three phenolic compounds. Let's denote them as:
- A: Aliphatic alcohol
- B: Simple phenol
- C: Substituted phenol with an electron-donating group (e.g., -CH₃)
- D: Substituted phenol with an electron-withdrawing group (e.g., -NO₂)

### Step 2: Compare the Acidity of Alcohols and Phenols
We know from chemical principles that alcohols are generally less acidic than phenols. This is because phenols can stabilize the negative charge on the oxygen atom after losing a proton (H⁺) due to resonance stabilization, while alcohols cannot.

**Conclusion from Step 2:**
- A (aliphatic alcohol) is less acidic than B, C, and D. Therefore, we can eliminate option A.

### Step 3: Analyze the Substituted Phenols
Now we need to compare the acidity of the phenolic compounds (B, C, and D):
- B: Simple phenol
- C: Substituted phenol with an electron-donating group (e.g., -CH₃)
- D: Substituted phenol with an electron-withdrawing group (e.g., -NO₂)

### Step 4: Understand the Effect of Substituents
- **Electron-donating groups (like -CH₃)** decrease the acidity of phenols because they push electron density towards the aromatic ring, making it less favorable for the phenol to lose a proton.
- **Electron-withdrawing groups (like -NO₂)** increase the acidity of phenols because they pull electron density away from the aromatic ring, stabilizing the negative charge on the oxygen after deprotonation.

### Step 5: Compare the Acidity of B, C, and D
- Since B is a simple phenol, it has moderate acidity.
- C (with -CH₃) will be less acidic than B due to the electron-donating effect.
- D (with -NO₂) will be more acidic than both B and C due to the electron-withdrawing effect.

### Final Conclusion
Among the options, the most acidic compound is D (the substituted phenol with the electron-withdrawing group -NO₂).