Which of the nitrogen atoms in `underset(I)(H_(2)N)-underset(II)(NH)-overset(O)overset(||)(C )-underset(III)(NH_(2))` is the most nucleophilic ?

Options

A. III
B. I
C. II
D. All three nitrogen atoms are equally strong nuclephilic centers.

Explanation

To determine which nitrogen atom in the compound `H2N-NH-C(=O)-NH2` is the most nucleophilic, we can analyze the structure and the electronic environment of each nitrogen atom.

### Step-by-Step Solution:

1. **Identify the Nitrogen Atoms**:
The compound contains three nitrogen atoms:
- Nitrogen I (N1): The first nitrogen in the `H2N` group.
- Nitrogen II (N2): The nitrogen attached directly to the carbonyl (C=O).
- Nitrogen III (N3): The nitrogen in the `NH2` group at the end.

2. **Understand Nucleophilicity**:
Nucleophilicity refers to the ability of a species to donate a pair of electrons to an electrophile. Nucleophiles are typically electron-rich species. The more available the lone pair of electrons on a nitrogen atom, the more nucleophilic it is.

3. **Analyze the Lone Pairs**:
- **N1 (H2N)**: This nitrogen has two hydrogen atoms attached and has a lone pair of electrons. Its lone pair is available for donation.
- **N2 (NH)**: This nitrogen is bonded to a carbonyl group (C=O). The presence of the carbonyl group can withdraw electron density through resonance, making the lone pair less available for nucleophilic attack.
- **N3 (NH2)**: Similar to N1, this nitrogen has two hydrogen atoms and a lone pair of electrons that is available for donation.

4. **Consider the Effect of Conjugation**:
- The lone pair on N2 is involved in resonance with the carbonyl group, which decreases its availability for nucleophilic attack. This is because the lone pair can participate in stabilizing the carbonyl, making it less nucleophilic.
- The lone pairs on N1 and N3 are not involved in such resonance and are thus more available for nucleophilic attack.

5. **Compare Nucleophilicity**:
- N1 and N3 both have available lone pairs, but N1 (H2N) is likely to be more nucleophilic than N3 (NH2) because it is less sterically hindered and has a stronger electron-donating effect due to the presence of two hydrogen atoms.
- N2 (NH) is the least nucleophilic due to resonance with the carbonyl group.

6. **Conclusion**:
Therefore, the most nucleophilic nitrogen atom in the compound is **Nitrogen I (N1)**.

### Final Answer:
The most nucleophilic nitrogen atom in the compound is **Nitrogen I (N1)**.