Consider the following compounds
1. Phenol
2. o - chlorophenol
3. m - chloropheonl
4. p - chlorophenol
Place these compounds in the decreasing order of acidity

Options

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

Answer

To determine the decreasing order of acidity for the compounds given (Phenol, o-chlorophenol, m-chlorophenol, and p-chlorophenol), we need to analyze the effects of the chlorine substituent on the acidity of phenol.

### Step 1: Understand Acidity
Acidity is the ability of a compound to donate a proton (H+). The stability of the resulting negative charge (conjugate base) after deprotonation is crucial in determining the strength of the acid. The more stable the conjugate base, the stronger the acid.

### Step 2: Analyze Phenol
- **Phenol (C6H5OH)**: When phenol donates a proton, it forms the phenoxide ion (C6H5O−). The negative charge on the oxygen is stabilized by resonance with the aromatic ring, making phenol a weak acid.

### Step 3: Analyze o-Chlorophenol
- **o-Chlorophenol**: The chlorine atom is an electron-withdrawing group (due to its electronegativity) and can stabilize the negative charge on the phenoxide ion through resonance (ortho effect). This stabilization increases the acidity compared to phenol.

### Step 4: Analyze m-Chlorophenol
- **m-Chlorophenol**: The chlorine atom is in the meta position. In this case, it does not participate in resonance with the negative charge on the oxygen. The only effect it has is a -I (inductive effect), which slightly decreases the acidity compared to phenol, but not as much as o-chlorophenol.

### Step 5: Analyze p-Chlorophenol
- **p-Chlorophenol**: The chlorine atom is in the para position. Similar to o-chlorophenol, it can stabilize the negative charge on the phenoxide ion through resonance. This makes p-chlorophenol more acidic than both phenol and m-chlorophenol.

### Step 6: Order the Acidity
Based on the analysis:
1. **o-Chlorophenol** (most acidic due to strong resonance stabilization)
2. **p-Chlorophenol** (also has resonance stabilization but less effective than ortho)
3. **Phenol** (moderate acidity due to resonance stabilization)
4. **m-Chlorophenol** (least acidic due to lack of resonance stabilization)

### Final Order of Acidity
The decreasing order of acidity is:
**o-Chlorophenol > p-Chlorophenol > Phenol > m-Chlorophenol**