The organic chloro compound, which shows complete stereochemical inversion during a ` S_(N^2) ` reaction is

Options

A. `(C_2 H_5 )_2 CHCl`
B. `(CH_3 )_3 C Cl`
C. `(CH_3)_2 CHCl`
D. `CH_3 Cl`

Explanation

To determine which organic chloro compound shows complete stereochemical inversion during an SN2 reaction, we need to analyze the options provided:

1. **Understanding SN2 Mechanism**:
- The SN2 (bimolecular nucleophilic substitution) mechanism involves a nucleophile attacking the carbon atom that is bonded to the leaving group (in this case, chlorine).
- The nucleophile approaches from the opposite side of the leaving group, leading to a backside attack. This results in the inversion of configuration at the carbon atom, known as Walden inversion.

2. **Analyzing the Options**:
- **Option A: 3-chloropentane**: This is a tertiary alkyl halide. Tertiary halides do not undergo SN2 reactions due to steric hindrance.
- **Option B: 2-methyl-2-chloropropane**: This is also a tertiary alkyl halide, which will not undergo SN2 reactions.
- **Option C: 2-chloropropane**: This is a secondary alkyl halide. While it can undergo SN2 reactions, the inversion may not be complete due to steric hindrance.
- **Option D: Chloromethane**: This is a primary alkyl halide. Primary halides are most reactive in SN2 reactions due to less steric hindrance, allowing for complete stereochemical inversion.

3. **Conclusion**:
- The organic chloro compound that shows complete stereochemical inversion during an SN2 reaction is **option D: chloromethane**.

### Step-by-Step Solution:
1. **Identify the SN2 mechanism**: Understand that SN2 involves a backside attack leading to inversion.
2. **Evaluate each compound**:
- **3-chloropentane**: Tertiary, does not undergo SN2.
- **2-methyl-2-chloropropane**: Tertiary, does not undergo SN2.
- **2-chloropropane**: Secondary, may undergo but not complete inversion.
- **Chloromethane**: Primary, undergoes SN2 with complete inversion.
3. **Select the correct option**: Chloromethane (option D) is the correct answer.