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

### Step 1: Identify the Compounds
We need to identify the compounds in question. Let's assume we have the following compounds:
1. C6H5-CH=CH-Cl (Chlorostyrene)
2. C6H5-CH=CH-CH3 (Allylbenzene)
3. C6H5-CH=CH-OCH3 (Methoxyallylbenzene)
4. C6H5-CH2-CH=CH2 (Allylbenzene)

### Step 2: Analyze Resonance Effects
- **Chlorostyrene (C6H5-CH=CH-Cl)**: The chlorine atom can participate in resonance due to its lone pairs. The C-Cl bond can exhibit some double bond character due to resonance, which shortens the bond length.

- **Allylbenzene (C6H5-CH=CH-CH3)**: The C-Cl bond does not have significant resonance stabilization compared to chlorostyrene, as there is no electronegative atom pulling electron density away from the bond.

- **Methoxyallylbenzene (C6H5-CH=CH-OCH3)**: The methoxy group (OCH3) is an electron-donating group through resonance, which can stabilize the positive charge but does not significantly affect the C-Cl bond length.

- **Allylbenzene (C6H5-CH2-CH=CH2)**: Similar to the previous allylbenzene, it does not have resonance effects that would shorten the C-Cl bond.

### Step 3: Compare the C-Cl Bonds
Now we compare the C-Cl bond lengths based on the resonance effects:
- **Chlorostyrene** has resonance that gives the C-Cl bond some double bond character, making it shorter.
- **Allylbenzene** and **Allylbenzene** do not significantly affect the C-Cl bond length.
- **Methoxyallylbenzene** has some resonance but is less effective than chlorostyrene.

### Conclusion
Based on the resonance and the effects of substituents, **Chlorostyrene (C6H5-CH=CH-Cl)** has the shortest C-Cl bond due to the resonance stabilization provided by the chlorine atom.

### Final Answer
The compound with the shortest C-Cl bond is **Chlorostyrene (C6H5-CH=CH-Cl)**.

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