Which one of the following compounds has the most acidic nature ?

Options

A.
B.
C.
D.

Answer

To determine which compound has the most acidic nature among the given options, we need to analyze the structure and the electron-donating or withdrawing effects of each compound. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand Acidity
- Acids are substances that can donate a proton (H⁺ ion). The ease of proton donation is influenced by the stability of the resulting anion after proton donation.
- Electron-donating groups (EDGs) increase electron density on the hydroxyl group (–OH), making it harder to lose H⁺, thus decreasing acidity.
- Electron-withdrawing groups (EWGs) decrease electron density on the hydroxyl group, making it easier to lose H⁺, thus increasing acidity.

### Step 2: Analyze Each Compound
1. **Benzyl Alcohol (C₆H₅CH₂OH)**:
- The benzene ring has a weak electron-withdrawing effect (due to resonance) but the CH₂ group is electron-donating (due to +I effect).
- Overall, the electron-donating effect dominates, making it less acidic.

2. **Phenol (C₆H₅OH)**:
- The –OH group is directly attached to the benzene ring, which can stabilize the negative charge on the oxygen through resonance.
- The benzene ring exerts a –R (resonance) effect, pulling electrons away from the –OH group, thus making it easier to lose H⁺.
- This makes phenol more acidic compared to benzyl alcohol.

3. **Cyclohexanol (C₆H₁₁OH)**:
- The –OH group is attached to a saturated carbon in a cyclohexane ring.
- The cyclohexane ring is electron-donating (+I effect), which increases electron density on the –OH group, making it less acidic.

4. **Aliphatic Alcohol (R-OH)**:
- Similar to cyclohexanol, aliphatic alcohols have –OH groups attached to saturated carbons.
- These groups also exhibit +I effects, making them less acidic due to increased electron density on the –OH group.

### Step 3: Compare Acidity
- **Benzyl Alcohol**: Less acidic due to the dominance of +I effect from CH₂.
- **Phenol**: Most acidic due to resonance stabilization of the negative charge after losing H⁺.
- **Cyclohexanol**: Less acidic due to +I effect from the cyclohexane ring.
- **Aliphatic Alcohol**: Less acidic due to +I effect from the aliphatic carbon.

### Conclusion
Among the compounds analyzed, **Phenol (C₆H₅OH)** has the most acidic nature due to the resonance stabilization provided by the benzene ring, which facilitates the loss of the H⁺ ion.

### Final Answer
**Phenol is the most acidic compound among the given options.**

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