Nucelophilic aliphatic substitution reaction is given by those compounds which have nucleophiic groups as leaving. Less is the basicity of the leaving group. More is its leaving power. Leaving group in the form of nucleophile (charged of neutral)
Leaving power of which group is maximum ?
Which one of the following compounds may NOT given SN reaction ?

Options

A. `R-overset(o+)N-=N`
B. `R-O-SO_(2)-CH_(3)`
C. `R-NH_(2)`
D. `R-overset(o+)underset(H)underset(|)O-H`

Answer

To solve the question regarding nucleophilic aliphatic substitution reactions and the leaving groups, we will analyze the leaving groups based on their basicity and stability.

### Step-by-Step Solution:

1. **Understanding Leaving Groups**:
- In nucleophilic substitution reactions (SN1 and SN2), the leaving group is the atom or group that departs with a pair of electrons. The better the leaving group, the more likely the reaction will proceed.
- A good leaving group is typically a weak base because weak bases are more stable when they leave.

2. **Identifying the Leaving Groups**:
- The question presents several leaving groups:
1. N2 (from N≡N)
2. OSO2CH3
3. NH2^−
4. H2O

3. **Evaluating Each Leaving Group**:
- **N2 (Dinitrogen)**:
- When nitrogen leaves as N2, it forms a very stable molecule due to the strong triple bond. Thus, it is an excellent leaving group.
- **OSO2CH3 (Methanesulfonate)**:
- This group can stabilize the leaving charge through resonance, making it a good leaving group.
- **NH2^− (Amide ion)**:
- This is a strong base and therefore a poor leaving group. It does not stabilize the negative charge well.
- **H2O (Water)**:
- Water is neutral and can stabilize the leaving charge, making it a good leaving group.

4. **Ranking the Leaving Groups**:
- Based on the stability and basicity of the leaving groups, we can rank them:
1. N2 (best leaving group)
2. H2O
3. OSO2CH3
4. NH2^− (worst leaving group)

5. **Conclusion on Leaving Power**:
- The leaving group with the maximum leaving power is **N2**.
- The compound that may NOT give an SN reaction is the one with **NH2^−**, as it is a poor leaving group.

### Final Answers:
- **Maximum Leaving Power**: N2
- **Compound that may NOT give SN reaction**: NH2^−