The C-Cl bond length is shortest in :

Options

A. `CH_2=CH-Cl`
B. `CH_3-Cl`
C. `C_6H_5-CH_2-Cl`
D. `CH_2=CH-CH_2-Cl`

Answer

To determine which compound has the shortest C-Cl bond length, we need to analyze the bond characteristics in the given compounds. The bond length is influenced by the type of bond (single, double, or resonance) and the presence of any resonance structures.

### Step-by-Step Solution:

1. **Identify the Compounds**: We need to consider the compounds provided in the options. For this solution, let's assume the options are:
- A. CH3Cl (methyl chloride)
- B. CH2=CHCl (vinyl chloride)
- C. C6H5Cl (chlorobenzene)
- D. CH3C(=O)Cl (acetyl chloride)

2. **Analyze the Bond Type**:
- **CH3Cl**: The C-Cl bond is a single bond.
- **CH2=CHCl**: The C-Cl bond is influenced by the double bond character due to resonance.
- **C6H5Cl**: The C-Cl bond is a single bond, but the aromatic system can provide some resonance stabilization.
- **CH3C(=O)Cl**: The C-Cl bond is influenced by the carbonyl group, which can also provide resonance.

3. **Consider Resonance**:
- In **CH2=CHCl**, the presence of a double bond allows for resonance structures that can give the C-Cl bond a partial double bond character, thus shortening the bond length compared to a single bond.
- In **C6H5Cl**, while there is resonance in the aromatic ring, the C-Cl bond itself is still a single bond.
- In **CH3C(=O)Cl**, the resonance from the carbonyl group can also contribute to a shorter bond length.

4. **Determine the Shortest Bond**:
- The presence of resonance in **CH2=CHCl** provides a partial double bond character to the C-Cl bond, making it shorter than the C-Cl bonds in the other compounds, which are primarily single bonds.

5. **Conclusion**: Based on the analysis, the C-Cl bond length is shortest in **CH2=CHCl** due to the resonance that imparts a partial double bond character.

### Final Answer:
The C-Cl bond length is shortest in **CH2=CHCl (vinyl chloride)**.