Which of the following is the most reactive towards nucleophilic substitution reaction?

Options

A. `ClCH_2-CH=CH_2`
B. `CH_2=CH-Cl`
C. `CH_3CH=CH-Cl`
D. `C_6H_5Cl`

Explanation

To determine which compound is the most reactive towards nucleophilic substitution reactions among the given options, we need to analyze the structure of each compound and the nature of the carbon-chlorine bond in them.

### Step-by-Step Solution:

1. **Identify the Compounds**:
The compounds given are:
1. CH2=CH-CH2-Cl (1-chloropropene)
2. CH2=CH-Cl (vinyl chloride)
3. CH3-CH=CH-Cl (allylic chloride)
4. C6H5-Cl (chlorobenzene)

2. **Understand Nucleophilic Substitution**:
Nucleophilic substitution reactions involve the replacement of a leaving group (in this case, Cl) by a nucleophile. The reactivity of the carbon-chlorine bond is crucial for this process.

3. **Analyze the Bond Strength**:
- In **1-chloropropene**, the carbon-chlorine bond is a single bond, which is generally weaker and more reactive towards nucleophilic substitution.
- In **vinyl chloride**, the carbon-chlorine bond has partial double bond character due to resonance, making it less reactive.
- In **allylic chloride**, the carbon-chlorine bond is also a single bond but is stabilized by resonance with the adjacent double bond, which can make it less reactive than expected.
- In **chlorobenzene**, the carbon-chlorine bond has significant double bond character due to resonance with the aromatic ring, making it very stable and least reactive towards nucleophilic substitution.

4. **Compare Reactivity**:
- The order of reactivity towards nucleophilic substitution is generally: alkyl halides > allylic halides > vinyl halides > aryl halides.
- Therefore, 1-chloropropene (alkyl halide) will be the most reactive, followed by allylic chloride, vinyl chloride, and finally chlorobenzene.

5. **Conclusion**:
Based on the analysis, the most reactive compound towards nucleophilic substitution is **1-chloropropene (CH2=CH-CH2-Cl)**.

### Final Answer:
The most reactive towards nucleophilic substitution reaction is **1-chloropropene (CH2=CH-CH2-Cl)**.