In `S_(N)2` reactions, the correct order of reactivity for the following compounds:
`CH_(3)CI,CH_(3)CH_(2)CI,(CH_(3))_(2)CHCI` and `(CH_(3))_(2)C CI` is:

Options

A. `CH_(3)CH_(2)CI gt CH_(3)CI gt (CH_(3))_(2)CHCI gt (CH_(3))_(3)C C`
B. `(CH_(3))_(2)CHCI gt CH_(3)CH_(2)CI gt CH_(3)CI gt (CH_(3))_(3)C CI`
C. `CH_(3)CI gt (CH_(3))_(2) CHCI gt CH_(3)CI gt (CH_(3))_(3) C CI`
D. `CH_(3)CI gt CH_(3)CH_(2)CI gt (CH_(3))_(2)CHCI gt (CH_(3))_(3)C CI`

Answer

To determine the correct order of reactivity for the given compounds in \( S_N2 \) reactions, we need to consider the concept of steric hindrance and the structure of each compound. The \( S_N2 \) mechanism involves a nucleophile attacking the carbon atom bonded to the halogen, and steric hindrance plays a crucial role in this process.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- \( CH_3Cl \) (Methyl chloride)
- \( CH_3CH_2Cl \) (Ethyl chloride)
- \( (CH_3)_2CHCl \) (Isopropyl chloride)
- \( (CH_3)_3CCl \) (Tert-butyl chloride)

2. **Determine the Type of Halides**:
- \( CH_3Cl \) is a **primary alkyl halide**.
- \( CH_3CH_2Cl \) is also a **primary alkyl halide**.
- \( (CH_3)_2CHCl \) is a **secondary alkyl halide**.
- \( (CH_3)_3CCl \) is a **tertiary alkyl halide**.

3. **Assess Steric Hindrance**:
- In \( S_N2 \) reactions, steric hindrance affects the reactivity. The more crowded the carbon atom (the one attached to the halogen), the less reactive it is in \( S_N2 \) reactions.
- **Methyl halide** (\( CH_3Cl \)) has the least steric hindrance.
- **Ethyl halide** (\( CH_3CH_2Cl \)) has slightly more hindrance but is still primary.
- **Isopropyl halide** (\( (CH_3)_2CHCl \)) has more steric hindrance due to two methyl groups.
- **Tert-butyl halide** (\( (CH_3)_3CCl \)) has the most steric hindrance due to three methyl groups.

4. **Order of Reactivity**:
- The order of reactivity in \( S_N2 \) reactions is inversely proportional to steric hindrance:
- **Most reactive**: \( CH_3Cl \) (least steric hindrance)
- **Next**: \( CH_3CH_2Cl \) (primary)
- **Then**: \( (CH_3)_2CHCl \) (secondary)
- **Least reactive**: \( (CH_3)_3CCl \) (tertiary)

5. **Final Order**: Therefore, the correct order of reactivity for the compounds in \( S_N2 \) reactions is:
\[ CH_3Cl > CH_3CH_2Cl > (CH_3)_2CHCl > (CH_3)_3CCl \]