Question

Rank the following compounds in order of increasing basicity.

• A. 4<2<1<3
• B. 4<1<3<2
• C. 4<3<1<2
• D. 2<1<3<4

Hint:

Remember that electron-donating groups increase basicity, while electron-withdrawing groups decrease basicity.

Answer 1

The Correct Option is C

In this case, the basicity of the compounds is influenced by the electron-withdrawing or electron-donating groups attached to the benzene ring. The amino group (-NH\(_2\)) is an electron-donating group, which increases the basicity of the compound. 
In contrast, electron-withdrawing groups like -NO\(_2\) or -Cl will decrease the basicity of the compound. 

- Compound 1: The amino group (-NH\(_2\)) is electron-donating, increasing the basicity. 
- Compound 2: The -Cl group is electron-withdrawing, making the compound less basic. 
- Compound 3: The -NO\(_2\) group is strongly electron-withdrawing, further decreasing basicity compared to compound 2. 
- Compound 4: The amino group (-NH\(_2\)) is present again, but the -NO\(_2\) group is also attached, significantly reducing its basicity. 

Thus, the order of increasing basicity is: 4<3<1<2.

Answer 2

To rank the given compounds in order of increasing basicity, we must consider the electron-donating and electron-withdrawing effects of the substituents on the amine nitrogen. Basicity is influenced by the ability of the compound to donate a lone pair of electrons.

The compounds provided likely have various substituents that affect the availability of the lone pair on the nitrogen atom:

1. Electronic Effects: Electron-donating groups (EDGs) increase basicity by increasing electron density on the nitrogen, making it more likely to donate electrons. Conversely, electron-withdrawing groups (EWGs) decrease basicity.
2. Inductive Effects: EWGs reduce the basicity through the inductive effect by pulling electron density away from the nitrogen.
3. Resonance Effects: If the lone pair can participate in resonance, it might be less available for protonation, reducing basicity.

Given these principles, we can analyze the compounds:

1. Compound 4 likely has strong EWGs or resonance stabilization of nitrogen's lone pair, making it the least basic.
2. Compound 3, though possibly less stabilized than compound 4, still has significant EWG impact.
3. Compound 1 might have lesser EWGs or more EDGs, making it more basic than compound 3.
4. Compound 2 is expected to have the most EDGs or least impact of EWGs, making it the most basic.

Thus, the order of increasing basicity is:

4<3<1<2