Consider the following three halides:
1. `CH_(3)-CH_(2)-Cl`
2. `CH_(2)=CH-Cl`
3. `C_(6)H_(5)-Cl`
Arrange C-Cl bond length of these compounds in decreasing order

Options

A. `1gt2gt3`
B. `1gt3gt2`
C. `3gt2gt1`
D. `2gt3gt1`

Answer

To determine the order of C-Cl bond lengths in the three halides provided, we need to analyze the hybridization of the carbon atoms in each compound and the resonance structures that may affect the bond character.

### Step-by-Step Solution:

1. **Identify the Compounds**:
- Compound 1: `CH3-CH2-Cl` (1-chloroethane)
- Compound 2: `CH2=CH-Cl` (vinyl chloride)
- Compound 3: `C6H5-Cl` (chlorobenzene)

2. **Determine the Hybridization**:
- For **Compound 1** (`CH3-CH2-Cl`):
- The carbon atoms are sp³ hybridized.
- % s-character = 25% (since sp³ has 25% s-character).
- Longer bond length due to lower s-character.

- For **Compound 2** (`CH2=CH-Cl`):
- The carbon atom attached to Cl is sp² hybridized.
- % s-character = 33.3% (since sp² has 33.3% s-character).
- Shorter bond length compared to sp³ due to higher s-character.

- For **Compound 3** (`C6H5-Cl`):
- The carbon atom attached to Cl is also sp² hybridized.
- % s-character = 33.3%.
- However, resonance in chlorobenzene affects the bond character.

3. **Analyze Resonance Structures**:
- **Compound 1** has no resonance; thus, the C-Cl bond is a typical single bond.
- **Compound 2** has limited resonance structures, but the C-Cl bond is primarily a single bond.
- **Compound 3** has significant resonance due to the aromatic ring, which allows for partial double bond character in the C-Cl bond. This leads to a shorter bond length.

4. **Compare Bond Lengths**:
- The C-Cl bond in **Compound 1** is the longest due to sp³ hybridization and no resonance.
- The C-Cl bond in **Compound 2** is shorter than that in Compound 1 but longer than that in Compound 3 due to sp² hybridization and limited resonance.
- The C-Cl bond in **Compound 3** is the shortest due to resonance contributing to partial double bond character.

5. **Final Arrangement**:
- The order of C-Cl bond lengths in decreasing order is:
1. `CH3-CH2-Cl` (longest)
2. `CH2=CH-Cl`
3. `C6H5-Cl` (shortest)

### Conclusion:
The decreasing order of C-Cl bond lengths is:
1. `CH3-CH2-Cl` > 2. `CH2=CH-Cl` > 3. `C6H5-Cl`