Q3 / 180 · COMEDK 2024 (Morning Shift) · Chemistry
Which one of the following shows the correct increasing order of basic nature of the given compounds?
A: Phenylmethanamine
B: N-Ethylethanamine
C:N, N-Dimethylaniline
D : N, N-Dimethylmethanamine
- AA < D < B < C
- Correct answerBC < A < D < B
- C$\mathrm{B}<\mathrm{C}<\mathrm{A}<\mathrm{D}$
- DD < B < A < C
Solution
The basicity of amines depends on the availability of the lone pair on the nitrogen atom. Electron-donating groups increase basicity, while electron-withdrawing groups or resonance delocalization decrease it.
Compound A is Phenylmethanamine ($C_{6}H_{5}CH_{2}NH_{2}$), a primary amine where the lone pair is not delocalized into the ring, but the phenyl group exerts a weak inductive effect. It is more basic than aromatic amines but less basic than aliphatic amines.
Compound B is N-Ethylethanamine ($(C_{2}H_{5})_{2}NH$), a secondary aliphatic amine. Secondary aliphatic amines are generally the most basic due to the strong inductive effect of two alkyl groups and favorable solvation.
Compound C is N,N-Dimethylaniline ($C_{6}H_{5}N(CH_{3})_{2}$), a tertiary aromatic amine. The lone pair on the nitrogen is delocalized into the benzene ring, making it the least basic among the given compounds.
Compound D is N,N-Dimethylmethanamine ($(CH_{3})_{3}N$), a tertiary aliphatic amine. While it has three electron-donating methyl groups, its basicity is often lower than secondary amines due to steric hindrance and solvation effects in aqueous media.
Comparing the basicity: C (aromatic) < A (primary aliphatic/aromatic-like) < D (tertiary aliphatic) < B (secondary aliphatic).
Thus, the increasing order is C < A < D < B.
Answer: C < A < D < B
Compound A is Phenylmethanamine ($C_{6}H_{5}CH_{2}NH_{2}$), a primary amine where the lone pair is not delocalized into the ring, but the phenyl group exerts a weak inductive effect. It is more basic than aromatic amines but less basic than aliphatic amines.
Compound B is N-Ethylethanamine ($(C_{2}H_{5})_{2}NH$), a secondary aliphatic amine. Secondary aliphatic amines are generally the most basic due to the strong inductive effect of two alkyl groups and favorable solvation.
Compound C is N,N-Dimethylaniline ($C_{6}H_{5}N(CH_{3})_{2}$), a tertiary aromatic amine. The lone pair on the nitrogen is delocalized into the benzene ring, making it the least basic among the given compounds.
Compound D is N,N-Dimethylmethanamine ($(CH_{3})_{3}N$), a tertiary aliphatic amine. While it has three electron-donating methyl groups, its basicity is often lower than secondary amines due to steric hindrance and solvation effects in aqueous media.
Comparing the basicity: C (aromatic) < A (primary aliphatic/aromatic-like) < D (tertiary aliphatic) < B (secondary aliphatic).
Thus, the increasing order is C < A < D < B.
Answer: C < A < D < B
Hence, the correct answer is option: 'B'.