9701 · 34.1
Primary and secondary amines — FAQ
Frequently asked questions for 9701 Primary and secondary amines. Direct answers first, then deeper explanation — then practise with marking.
Why are secondary amines often the strongest bases among the simple alkylamines?
It's a balance of two factors in aqueous solution. Firstly, secondary amines have two electron-donating alkyl groups, making the lone pair more available than in primary amines (the +I effect). Secondly, the resulting ammonium ion (R₂NH₂⁺) is well-stabilised by solvation (hydrogen bonding with water). Tertiary amines have three alkyl groups (strongest +I effect), but their corresponding ammonium ion (R₃NH⁺) is sterically hindered, leading to less effective solvation, which slightly reduces their basicity compared to secondary amines.
What is a quaternary ammonium salt and how is it different from an amine?
A quaternary ammonium salt has four alkyl or aryl groups bonded to the nitrogen atom, giving the nitrogen a permanent positive charge (e.g., [R₄N]⁺X⁻). Unlike amines, it has no lone pair of electrons on the nitrogen and therefore cannot act as a base or a nucleophile. These salts are often used as surfactants and disinfectants.
Can tertiary amines react with acyl chlorides to form amides?
No, tertiary amines cannot form amides with acyl chlorides because they do not have a hydrogen atom attached to the nitrogen. The nucleophilic addition-elimination mechanism requires the elimination of a small molecule, which is HCl in the case of primary/secondary amines. Without an N-H bond, this elimination cannot occur to form a stable neutral amide product.