In which compounds (II) is more basic than (I)

Options

A.
B. `underset((I))(H_(2)N-overset(O)overset(||)C-NH_(2)) & underset((II))(H_(2)N-overset(NH)overset(||)C-NH_(2))`
C.
D. `underset((I))(CH_(3)NH_(2)) & underset((II))((CH_(3))_(2)NH)`

Answer

To determine in which compounds (II) is more basic than (I), we need to analyze the structures and the factors affecting the basicity of the compounds. Basicity is influenced by the availability of the lone pair of electrons on the nitrogen atom, which can be affected by electron-donating or electron-withdrawing groups attached to it.

### Step-by-Step Solution:

1. **Identify the Compounds:**
- Let's denote compound (I) as Compound 1 and compound (II) as Compound 2.
- For example, let’s consider the following pairs:
- (I) Diethylamine (C2H5)2NH
- (II) N,N-Diethylamine (C2H5)2N

2. **Analyze the Electron-Donating Effects:**
- In Compound 1, the ethyl groups (C2H5) are electron-donating through the +I (inductive) effect. This increases the electron density on the nitrogen atom, making it more basic.
- In Compound 2, the same ethyl groups are present, and they also provide a +I effect.

3. **Consider Steric Hindrance:**
- In Compound 1, the nitrogen atom is less sterically hindered compared to Compound 2. This means that the lone pair of electrons on nitrogen can be more available for bonding with protons (H+).
- In Compound 2, the presence of two ethyl groups increases steric hindrance, which can make the lone pair less available.

4. **Evaluate the Conjugation Effects:**
- For other pairs such as urea (Compound 1) and hydrazine (Compound 2), the nitrogen in hydrazine can participate in resonance, which stabilizes the molecule and increases basicity.
- In urea, the carbonyl group (C=O) withdraws electron density through resonance, making the nitrogen less basic.

5. **Compare the Basicity:**
- In the first pair, Compound 2 (N,N-Diethylamine) is more basic than Compound 1 (Diethylamine) due to the greater electron density provided by the ethyl groups, despite steric hindrance.
- In the second pair, Compound 2 (hydrazine) is more basic than Compound 1 (urea) due to the ability of nitrogen to donate its lone pair more readily without resonance stabilization.
- In the third pair, Compound 2 (pyridine) is more basic than Compound 1 (diethylamine) due to the availability of the lone pair on nitrogen.
- In the fourth pair, Compound 2 (dimethylamine) is more basic than Compound 1 (methylamine) due to the presence of two electron-donating methyl groups.

### Conclusion:
In all the analyzed cases, Compound (II) is more basic than Compound (I).