Three gaseous alkylamines A, B and C or primary, secondary and tertiary respectively. What will be the correct order of their basicity?

C > B > A

Explanation:

Inductive Effect (+I Effect): Alkyl groups are electron-donating via the inductive effect, increasing the electron density on nitrogen and making it more available for protonation. More alkyl groups enhance this effect, making tertiary amines (C) the most basic, followed by secondary (B), and then primary (A).

Absence of Solvation Effect: In aqueous solutions, hydrogen bonding stabilizes the conjugate acid of primary and secondary amines, making them more basic than tertiary amines. However, in the gas phase, solvation effects are absent, and only the intrinsic electron-donating ability of alkyl groups matters.

Steric Hindrance (Less Significant in Gas Phase): In aqueous solutions, steric hindrance in tertiary amines makes protonation difficult. But in the gas phase, steric hindrance does not play a major role in preventing protonation. Thus, the basicity increases with the number of alkyl groups.

Therefore, Tertiary amine (C) > Secondary amine (B) > Primary amine (A)