Consider the following statements about the basic strength of amines.
(A) The basic character of an amine depends upon the ease of formation of the cation by accepting a proton from the acid.
(B) The substituted ammonium ion formed from an alkylamine is stabilised by dispersal of the positive charge by the +I effect of the alkyl group.
(C) In the aqueous phase, the greater the size of the substituted ammonium ion, the greater is its solvation.
(D) Aromatic amines are weaker bases than ammonia due to the electron releasing nature of the aryl group.
(E) In aqueous solution, a small alkyl group such as –CH3 causes no steric hindrance to H-bonding.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (C) and (D) only
An amine is a stronger base when the cation it forms by taking a proton is more stable compared with the amine. In water, this stability comes from the +I effect of alkyl groups and from solvation (H-bonding with water), which steric hindrance can reduce.
(A) The basic character of an amine depends upon the ease of formation of the cation by accepting a proton from the acid. — Correct statement. The more stable the cation is relative to the amine, the more basic is the amine.
(B) The substituted ammonium ion formed from an alkylamine is stabilised by dispersal of the positive charge by the +I effect of the alkyl group. — Correct statement. This is one reason why alkylamines are stronger bases than ammonia.
(C) In the aqueous phase, the greater the size of the substituted ammonium ion, the greater is its solvation. — Incorrect statement. A larger ion is less solvated by water molecules and so is less stabilised.
(D) Aromatic amines are weaker bases than ammonia due to the electron releasing nature of the aryl group. — Incorrect statement. The aryl group is electron withdrawing; it pulls the unshared electron pair of nitrogen into the ring, so the pair is less available for a proton.
(E) In aqueous solution, a small alkyl group such as –CH3 causes no steric hindrance to H-bonding. — Correct statement. Steric hindrance to H-bonding appears only when the alkyl group is bigger than –CH3, for example –C2H5.
NCERT (2026-27 edition):
9.6 Chemical Reactions – “Basic character of an amine depends upon the ease of formation of the cation by accepting a proton from the acid. The more stable the cation is relative to the amine, more basic is the amine.”
“…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.” … “In the aqueous phase, the substituted ammonium cations get stabilised not only by electron releasing effect of the alkyl group (+I) but also by solvation with water molecules. The greater the size of the ion, lesser will be the solvation and the less stabilised is the ion.”
“Secondly, when the alkyl group is small, like –CH3 group, there is no steric hindrance to H-bonding. In case the alkyl group is bigger than CH3 group, there will be steric hinderance to H-bonding.”
“On the other hand, aromatic amines are weaker bases than ammonia due to the electron withdrawing nature of the aryl group.”