Aliphatic amines are stronger bases than ammonia due to the +I effect of alkyl groups, leading to high electron density on the nitrogen atom. This effect is reflected in their pKb values, which range from 3 to 4.22.
What is the impact of +I effect of alkyl groups on the basicity of aliphatic amines, and how does it influence their pKb values?
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The +I (inductive) effect of alkyl groups in aliphatic amines enhances their basicity. Alkyl groups donate electron density through sigma bonds to the nitrogen atom, stabilizing the lone pair and increasing its availability for proton acceptance. This results in stronger basic character. The influence of +I effect is reflected in the pKb values; aliphatic amines with more alkyl substituents generally exhibit lower pKb values, indicating higher basicity. The increased electron-donating character of alkyl groups enhances the nucleophilicity of the amine, facilitating proton acceptance and reinforcing its role as a stronger base.