Which is the correct decreasing order of basic strength in aqueous medium

Options

A. `(CH_(3))_(3)Ngt(CH_(3))_(2)NHgtCH_(3)NH_(2)NH_(3)`
B. `(CH_(3))_(2)NHgtCH_(3)NH_(2)gt(CH_(3))_(3)NH_(3)`
C. `(CH_(3))_(2)NHgt(CH_(3))_(3)NgtCH_(3)NH_(2)gtNH_(3)`
D. `CH_(3)NH_(2)gt(CH_(3))_(2)NHgt(CH_(3))_(3)NgtNH_(3)`

Answer

To determine the correct decreasing order of basic strength in aqueous medium for amines, we can follow these steps:

### Step 1: Understand Basicity
Basicity refers to the ability of a compound to accept protons (H⁺ ions). In the case of amines, the nitrogen atom has a lone pair of electrons that can be used to bond with protons.

### Step 2: Analyze the Structure of Amines
Amines can be classified based on the number of alkyl groups attached to the nitrogen:
- **Primary amine (1°)**: One alkyl group attached to nitrogen.
- **Secondary amine (2°)**: Two alkyl groups attached to nitrogen.
- **Tertiary amine (3°)**: Three alkyl groups attached to nitrogen.

### Step 3: Evaluate the Effect of Alkyl Groups on Basicity
- **Steric Hindrance**: As the number of alkyl groups increases, steric hindrance also increases. This makes it more difficult for the nitrogen to donate its lone pair to bond with a proton.
- **Electron-donating Effect**: Alkyl groups are electron-donating, which increases the electron density on nitrogen, enhancing basicity.

### Step 4: Compare the Basic Strength
1. **Tertiary Amine (3°)**: Although it has three electron-donating groups, the steric hindrance makes it less basic because the nitrogen is crowded and less able to interact with protons.
2. **Secondary Amine (2°)**: It has less steric hindrance compared to tertiary amines, making it more basic.
3. **Primary Amine (1°)**: It has the least steric hindrance, allowing it to be more basic than secondary and tertiary amines.
4. **Ammonia (NH₃)**: Ammonia has no alkyl groups and is the least basic among the amines because it lacks the electron-donating effect of alkyl groups.

### Step 5: Establish the Order
Based on the analysis:
- The order of basic strength in aqueous medium is: **2° > 1° > 3° > NH₃**.

### Conclusion
Thus, the correct decreasing order of basic strength in aqueous medium is **2° > 1° > 3° > NH₃**.