Arrange the order of `C--OH` bond length of the following compounds. (A) Methanol (B) Phenol (C) p-Ethoxyphenol

Options

A. `"methanol"lt "p-etoxyphenol" lt "phenol"`
B. `"phenol" lt "methanol" lt "p-etoxyphenol" `
C. `"methanol" lt "phenol" lt "p-etoxyphenol" `
D. `"phenol" lt "p-etoxyphenol" lt "methanol" `

Answer

To determine the order of the C–OH bond lengths in the compounds methanol, phenol, and p-ethoxyphenol, we need to analyze the structures and the effects of resonance and hybridization on the bond lengths.

### Step 1: Draw the Structures
1. **Methanol (CH3OH)**: The structure consists of a carbon atom bonded to three hydrogen atoms and one hydroxyl group (–OH).
2. **Phenol (C6H5OH)**: This compound has a hydroxyl group attached to a benzene ring. The oxygen's lone pair can participate in resonance with the aromatic system.
3. **p-Ethoxyphenol (C6H4(OCH2CH3)OH)**: This compound has an ethoxy group (–OCH2CH3) attached to the benzene ring at the para position relative to the hydroxyl group. The ethoxy group can also participate in resonance with the ring.

### Step 2: Analyze Resonance Effects
- **Methanol**: The C–OH bond is purely a sigma bond with no resonance. Therefore, it has the longest bond length because there are no additional stabilizing interactions.

- **Phenol**: The lone pair of electrons on the oxygen can delocalize into the benzene ring, creating partial double bond character in the C–OH bond. This resonance leads to a shorter bond length compared to methanol.

- **p-Ethoxyphenol**: While there is resonance in this compound as well, the presence of the ethoxy group can hinder the resonance effect of the hydroxyl group. The ethoxy group donates electron density to the benzene ring, which can reduce the effective resonance of the hydroxyl group. As a result, the C–OH bond length is longer than in phenol but shorter than in methanol.

### Step 3: Order the C–OH Bond Lengths
Based on the analysis:
1. **Longest C–OH bond**: Methanol (A)
2. **Intermediate C–OH bond**: p-Ethoxyphenol (C)
3. **Shortest C–OH bond**: Phenol (B)

Thus, the order of C–OH bond lengths is:
**Methanol (A) > p-Ethoxyphenol (C) > Phenol (B)**

### Final Answer
The correct order of C–OH bond lengths is:
**A > C > B**