The reaction of amines with mineral acids to form ammonium salts shows that these are basic in nature. Amines have an unshared pair of electrons on the nitrogen atoms due to which they behave as Lewis bases. The basicity of amines is related to their structure. The basic character of an amine depends upon the ease of formation of a cation by accepting a proton from the acid. The more stable the cation is relative to the amine, the more basic the amine.
The correct order of basicity of amines in gas phase
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 1° < 2° < 3°
In the gas phase there is no solvent, so the solvation of the cation plays no part. Basicity then depends only on the +I effect of the alkyl groups: each alkyl group pushes electron density towards nitrogen, making the lone pair more available and stabilising the cation formed. The more alkyl groups, the stronger the base:
tertiary amine > secondary amine > primary amine > \( \ce{NH3} \)
NCERT (2026-27 edition):
Chemical Reactions – “… Due to the electron releasing nature of alkyl group, it pushes electrons towards nitrogen and thus makes the unshared electron pair more available for sharing with the proton of the acid. Moreover, the substituted ammonium ion formed from the amine gets stabilised due to dispersal of the positive charge by the +I effect of the alkyl group. Hence, alkylamines are stronger bases than ammonia. Thus, the basic nature of aliphatic amines should increase with increase in the number of alkyl groups. This trend is followed in the gaseous phase. The order of basicity of amines in the gaseous phase follows the expected order: tertiary amine > secondary amine > primary amine > NH3.”