In which compound C–Cl bond length is shortest

Options

A. (a) `Cl - CH=CH_2`
B. (b) `Cl–CH=CH–CH_3`
C. (c) `Cl–CH=CH–OCH_3`
D. (d) `Cl–CH=CH–NO_2`

Answer

To determine which compound has the shortest C–Cl bond length, we need to analyze the stability of the compounds based on their structures and the effects of substituents on the carbon atom bonded to chlorine. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
We have four compounds to analyze. Let's denote them as:
- Compound A
- Compound B
- Compound C
- Compound D

### Step 2: Understand Bond Lengths
The bond length between atoms is influenced by the type of bond (single, double, triple) and the stability of the molecule. Generally, the order of bond lengths from longest to shortest is:
- Single bond > Double bond > Triple bond

### Step 3: Analyze Each Compound
1. **Compound A**: Contains a C–Cl single bond. The presence of a single bond means it will have a longer bond length compared to a double bond.

2. **Compound B**: Also contains a C–Cl single bond. Similar reasoning applies as in Compound A.

3. **Compound C**: Contains a C–Cl bond that may involve resonance structures. The presence of electronegative groups can stabilize certain resonance forms, potentially leading to a shorter bond length if a double bond character is introduced.

4. **Compound D**: Contains a C–Cl bond with a nitro group (NO2) attached. The nitro group is highly electronegative and can stabilize the resonance structure, leading to a greater double bond character in the C–Cl bond.

### Step 4: Determine Stability and Bond Character
- **Compound A and B**: Both have single bonds, which are longer.
- **Compound C**: May have some resonance but not as strong as Compound D.
- **Compound D**: The presence of the nitro group allows for significant resonance stabilization, leading to a greater likelihood of a double bond character. This results in a shorter C–Cl bond length.

### Step 5: Conclusion
Based on the analysis, **Compound D** has the shortest C–Cl bond length due to the resonance stabilization provided by the nitro group, which increases the double bond character of the C–Cl bond.

### Final Answer
The compound with the shortest C–Cl bond length is **Compound D**.

---