Predict the compound which will undergo `S_(N)2` reaction faster:

Options

A. `CH_(3)-CH_(2)-CH_(2)-Cl`
B. `H_(3)C-overset(Cl)overset(|)C-CH_(3)`
C. `CH_(3)-CH_(2)-CH_(2)-l`
D. `H_(3)C-overset(Cl)overset(|)CH-CH_(3)`

Answer

To determine which compound will undergo an \( S_N2 \) reaction faster, we need to analyze the structure of each compound and their degree of substitution. The \( S_N2 \) reaction is favored by less hindered (less substituted) carbon centers. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Compounds
We have the following compounds:
1. **Compound A**: CH3-CH2-CH2-Cl (1-chloropropane)
2. **Compound B**: CH3-CH(CH3)-Cl (2-chloro-2-methylpropane)
3. **Compound C**: CH3-CH2-CH2-Cl (same as Compound A)
4. **Compound D**: CH3-CH3-CH3-Cl (t-butyl chloride)

### Step 2: Determine the Degree of Substitution
- **Compound A (1-chloropropane)**: The carbon attached to the chlorine is a primary carbon (1°), as it is attached to only one other carbon.
- **Compound B (2-chloro-2-methylpropane)**: The carbon attached to the chlorine is a tertiary carbon (3°), as it is attached to three other carbons.
- **Compound C**: This is identical to Compound A, so it is also a primary carbon (1°).
- **Compound D (t-butyl chloride)**: The carbon attached to the chlorine is also a tertiary carbon (3°).

### Step 3: Analyze the Reactivity
In \( S_N2 \) reactions, the rate of reaction decreases with increasing steric hindrance. Therefore, the order of reactivity based on the degree of substitution is:
- Primary (1°) > Secondary (2°) > Tertiary (3°)

### Step 4: Compare the Compounds
- **Compound A**: Primary (1°) – Fastest
- **Compound B**: Tertiary (3°) – Slowest
- **Compound C**: Primary (1°) – Fastest (same as A)
- **Compound D**: Tertiary (3°) – Slowest

### Conclusion
Since both Compound A and Compound C are primary and will react faster than the tertiary compounds (B and D), the correct answer is **Compound A (or C)**, as they will undergo the \( S_N2 \) reaction faster than the others.

### Final Answer
**The compound which will undergo \( S_N2 \) reaction faster is Compound A (or C).**

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