What will be the increasing order of basic strength of the following compounds: \(\text{C}_2\text{H}_5\text{NH}_2, (\text{C}_2\text{H}_5)_2\text{NH},(\text{C}_2\text{H}_5)_3\text{N},\text{C}_6\text{H}_5\text{NH}_2\)

Question

Which of the following reactions will not give a primary amine?

Answer 1

To rank basic strength in increasing order, consider factors influencing amine basicity:

Aliphatic vs. Aromatic Amines: Generally, aliphatic amines (e.g., C₂H₅NH₂, (C₂H₅)₂NH, (C₂H₅)₃N) are more basic than aromatic amines (e.g., C₆H₅NH₂). This is because the lone pair on the nitrogen in aromatic amines is delocalized into the benzene ring, reducing its availability for protonation.
Alkyl Groups: Electron-donating alkyl groups increase electron density on the nitrogen atom, thus enhancing basicity.
Steric Hindrance: In tertiary amines, bulky alkyl groups can impede proton approach, diminishing basicity.
Solvation Effects: In aqueous solutions, the solvation of the protonated amine is significant. Secondary amines typically exhibit greater solvation than tertiary amines.

Analysis of the compounds:

C₂H₅NH₂ (Ethylamine): A primary aliphatic amine.

(C₂H₅)₂NH (Diethylamine): A secondary aliphatic amine.

(C₂H₅)₃N (Triethylamine): A tertiary aliphatic amine.

C₆H₅NH₂ (Aniline): An aromatic amine.

Based on these factors:

Aniline (C₆H₅NH₂) exhibits the lowest basicity due to resonance delocalization.

Among aliphatic amines, secondary amines are generally the most basic, resulting from a combination of inductive and solvation effects.

Primary amines are less basic than secondary amines but more basic than tertiary amines, primarily due to steric hindrance in tertiary amines.

Therefore, the increasing order of basic strength is:

C₆H₅NH₂ < C₂H₅NH₂ < (C₂H₅)₃N < (C₂H₅)₂NH

The correct answer is:

Option 2: C₆H₅NH₂ < C₂H₅NH₂ < (C₂H₅)₃N < (C₂H₅)₂NH

The Correct Option is B