NGP (neighouring group of participation) assistance for `S_(N)2` reaction will not be seen in -

Options

A.
B. `CH_3-S-CH_2-CH_2-Cl`
C.
D.

Answer

To determine which compound does not exhibit Neighboring Group Participation (NGP) assistance for an \( S_N2 \) reaction, we need to analyze the conditions necessary for NGP to occur.

### Step-by-Step Solution:

1. **Understanding NGP**:
Neighboring Group Participation (NGP) occurs when a neighboring group (which can be a functional group or atom) assists in the leaving of a leaving group during a nucleophilic substitution reaction, specifically \( S_N2 \). For NGP to happen, the following conditions must be met:
- The leaving group must be a good leaving group.
- The neighboring group must have a lone pair of electrons or a double bond that can assist in the reaction.

2. **Identify the Compounds**:
We need to analyze the four given compounds to see which one does not meet the criteria for NGP. The compounds are not specified in the question, but we will assume they are typical examples where we can analyze the leaving groups and neighboring groups.

3. **Evaluate Each Compound**:
- **Compound 1**: If this compound has a good leaving group (e.g., Cl, Br, I) and a neighboring group with a lone pair or double bond, it can participate in NGP.
- **Compound 2**: Similar analysis as Compound 1. If it has a good leaving group and a neighboring group, it can also participate in NGP.
- **Compound 3**: Again, check for a good leaving group and a neighboring group.
- **Compound 4**: If this compound has a poor leaving group (e.g., -COOH) and lacks a neighboring group with a lone pair or double bond, it will not participate in NGP.

4. **Conclusion**:
After evaluating the compounds based on the criteria for NGP, the compound that has a poor leaving group (like -COOH) and does not have a neighboring group that can assist in the reaction will be the one that does not exhibit NGP assistance for \( S_N2 \) reactions.

### Final Answer:
The compound that does not show NGP assistance for \( S_N2 \) reaction is the one with a poor leaving group, likely the one containing -COOH.