Question

Arrange the following amines in the order of decreasing basic character in gaseous phase:
(A) NH₃ 
(B) (CH₃)₃N 
(C) (CH₃)₂NH 
(D) CH₃NH₂
Choose the correct answer from the options given below:

• A. (CH₃)NH₂, (CH₃)₂NH, (CH₃)₃N, NH₃
• B. (CH₃)₃N, (CH₃)₂NH, CH₃NH₂, NH₃
• C. (CH₃)₂NH, (CH₃)₃N, CH₃NH₂, NH₃
• D. (CH₃)₃N, (CH₃)₂NH, (CH₃)NH₂, NH₃

Hint:

The basicity of amines increases with the number of alkyl groups attached to the nitrogen atom. Alkyl groups donate electron density to the nitrogen, making its lone pair more available for protonation, which increases the basicity.

Answer 1

The Correct Option is B

The basic character of amines depends on the availability of the lone pair of electrons on the nitrogen atom, which can donate to a proton (H⁺) in the gaseous phase. Alkyl groups attached to nitrogen increase basicity by donating electron density through the inductive effect, thereby making the lone pair more available for protonation.

NH₃ (Ammonia): Ammonia has no alkyl groups and therefore the least electron-donating effect. Hence, it is the least basic.

CH₃NH₂ (Methylamine): The methyl group donates electron density to nitrogen, increasing the availability of the lone pair. Thus, methylamine is more basic than ammonia.

(CH₃)₂NH (Dimethylamine): The presence of two methyl groups further increases electron density on nitrogen, making dimethylamine more basic than methylamine.

(CH₃)₃N (Trimethylamine): Three methyl groups donate the maximum electron density to nitrogen, making trimethylamine the most basic among the given amines.

Thus, the order of basicity in the gaseous phase is: (CH₃)₃N > (CH₃)₂NH > CH₃NH₂ > NH₃.

Therefore, the correct answer is Option (2).