Which resonating structure of vinyl chloride is least stable :-

Options

A. `CH_(2) - CH - Cl`
B. `overset(oplus)CH_(2) - CH - overset(oplus)Cl`
C. `CH_(3) - CH - Cl`
D. All have equal stability

Answer

To determine which resonating structure of vinyl chloride is least stable, we need to analyze the structures based on two main criteria: the completeness of the octet and the distribution of charges. Let's break down the solution step by step.

### Step-by-Step Solution:

1. **Identify the Resonating Structures**:
Vinyl chloride (C2H3Cl) can have several resonating structures. We need to draw the possible structures to analyze their stability.

2. **Check the Octet Rule**:
For each resonating structure, we need to check if all atoms (especially carbon) have a complete octet (8 electrons).
- Carbon can form a maximum of 4 bonds.
- Each hydrogen can form 1 bond.
- Chlorine can form 1 bond and has 7 valence electrons.

3. **Count the Bonds**:
For each structure, count the number of bonds formed by each atom:
- In the first structure, if we have a double bond between the two carbons and single bonds to hydrogen and chlorine, we can count the total number of bonds.
- Repeat this for each resonating structure.

4. **Evaluate Charge Distribution**:
- If there are any charges in the structures, determine if they are located on electronegative or electropositive atoms.
- A negative charge on an electronegative atom (like chlorine) is more stable than on a carbon atom.

5. **Stability Assessment**:
- Structures where all atoms have complete octets and proper charge distribution are more stable.
- Compare the stability of the structures based on the above criteria.

6. **Identify the Least Stable Structure**:
- After analyzing all structures, identify which one has an incomplete octet or has unfavorable charge distribution. This structure will be the least stable.

### Conclusion:
Based on the analysis, the resonating structure that has an incomplete octet (specifically on a carbon atom) and potentially unfavorable charge distribution is the least stable. Therefore, the answer is that the third resonating structure is the least stable.