Which of the following has the shortest C - CI bond ?

Options

A. `Cl-CH=CH-NO_2`
B. `Cl-CH=CH-CH_3`
C. `Cl-CH=CH-OCH_3`
D. `Cl-CH=CH_2`

Answer

To determine which of the given compounds has the shortest C-Cl bond, we need to analyze the resonance structures and the effects of substituents on the bond length. Let's break down the solution step by step.

### Step 1: Identify the Compounds
The question provides several compounds that contain C-Cl bonds. We will analyze each one to see how the presence of substituents affects the bond length.

### Step 2: Understand the Effects of Substituents
- **Resonance Effect**: The presence of groups that can donate or withdraw electron density will affect the bond length. Electron-withdrawing groups (EWGs) can stabilize negative charges and increase bond character, while electron-donating groups (EDGs) can have the opposite effect.
- **Inductive Effect**: Groups that are electronegative can pull electron density away from the carbon, affecting the bond length.

### Step 3: Analyze Each Compound
1. **Compound 1: C-Cl with NO2 (Nitro group)**
- The nitro group is a strong electron-withdrawing group (-M effect).
- It can stabilize the positive charge that develops in resonance forms, leading to increased double bond character in the C-Cl bond.
- This results in a shorter C-Cl bond.

2. **Compound 2: C-Cl with CH3 (Methyl group)**
- The methyl group is an electron-donating group (+M effect).
- There is no resonance stabilization involving the C-Cl bond, leading to a longer bond length compared to the first compound.

3. **Compound 3: C-Cl with OCH3 (Methoxy group)**
- The methoxy group is also an electron-donating group (+M effect).
- Similar to the methyl group, it does not provide resonance stabilization for the C-Cl bond, resulting in a longer bond length.

4. **Compound 4: C-Cl with another substituent (not specified)**
- Without specific details, we can assume that if it does not have a strong electron-withdrawing group, it will not shorten the bond length significantly.

### Step 4: Conclusion
Based on the analysis, the compound with the nitro group (Compound 1) has the shortest C-Cl bond due to the resonance stabilization and the -M effect of the nitro group.

**Final Answer**: The compound with the shortest C-Cl bond is the one containing the nitro group (Compound 1).

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