Explain why aliphatic primary amines are generally more basic than aniline. In your answer discuss the role of resonance and inductive effects, and indicate how these effects influence the $K_{b}$ values.

hard 5 marks Class 12 · Chemistry · Amines

Answer

Aliphatic primary amines are more basic than aniline because the lone pair on nitrogen is not delocalised by resonance, and electron‑donating inductive effect of alkyl groups raises electron density, giving larger

K_{b}

(smaller

p K_{b}

) than aniline.

Step-by-step solution

Identify the key difference: in aniline the nitrogen lone pair can conjugate with the aromatic ring, while in aliphatic amines it cannot.
Explain resonance in aniline: the lone pair participates in delocalisation over the benzene ring, reducing its availability to accept a proton, which lowers basicity.
Describe the inductive effect of alkyl groups attached to aliphatic amines: alkyl groups donate electron density (+I effect) through sigma bonds, increasing the electron density on nitrogen and enhancing its ability to attract a proton.
Combine the two effects: lack of resonance delocalisation plus a positive inductive effect make aliphatic amines stronger bases.
Relate to $K_{b}$ : stronger bases have larger $K_{b}$ (or smaller $p K_{b}$ ). Typical $p K_{b}$ values are about 3.3 for methylamine versus 9.3 for aniline, illustrating the quantitative impact.

Common mistake: Attributing the lower basicity of aniline only to the electronegativity of the aromatic ring, ignoring the resonance delocalisation of the nitrogen lone pair.

Concept tested: Basicity comparison: aliphatic vs aromatic amines

Published 2 September 2026 · How this solution was prepared and checked

Explain why aliphatic primary amines are generally more basic than aniline. In your answer discuss the role of resonance and inductive effects, and indicate how these effects influence the Kb​ values.

Step-by-step solution

Related questions

Explain why aliphatic primary amines are generally more basic than aniline. In your answer discuss the role of resonance and inductive effects, and indicate how these effects influence the $K_{b}$ values.