The ionization constant of a phenol is higher than that of ethanol because

Options

A. Phenoxide ion is a stronger base than ethoxide ion
B. Phenoxide ion is stabilized through delocalisation
C. Phenoxide ion is less stable than ethoxide ion
D. Phenoxide ion is bulkier than ethoxide ion

Answer

To understand why the ionization constant of phenol is higher than that of ethanol, we will analyze the acidity of both compounds and the stability of their respective ions formed upon ionization.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- The two compounds in question are phenol (C6H5OH) and ethanol (C2H5OH).

2. **Understand Ionization**:
- Ionization constant (Ka) refers to the strength of an acid in solution. A higher ionization constant indicates a stronger acid.
- When phenol and ethanol dissolve in water, they ionize to form their respective ions:
- Phenol ionizes to form the phenoxide ion (C6H5O⁻).
- Ethanol ionizes to form the ethoxide ion (C2H5O⁻).

3. **Analyze the Ions**:
- The phenoxide ion (C6H5O⁻) has a negative charge that can be delocalized over the benzene ring due to resonance.
- The ethoxide ion (C2H5O⁻) does not have such resonance stabilization; the negative charge is localized on the oxygen atom.

4. **Resonance Stabilization**:
- In the phenoxide ion, the negative charge can be spread out over multiple atoms through resonance structures. This delocalization stabilizes the ion.
- In contrast, the ethoxide ion lacks this resonance, making it less stable.

5. **Conclusion on Acidity**:
- The stability of the phenoxide ion due to resonance means that phenol is more likely to donate a proton (H⁺), making it a stronger acid than ethanol.
- Therefore, the ionization constant of phenol is higher than that of ethanol because the phenoxide ion is stabilized through delocalization of the negative charge.

6. **Final Statement**:
- The ionization constant of phenol is higher than that of ethanol because the phenoxide ion is stabilized through delocalization, which enhances the acidity of phenol.