Amines as bases in comparison to ammonia

Question

Hi!

I wonder; why are amines stronger bases than ammonia, and why tertiary amines are stronger bases than primary amines?

I can't really find an answer in the internet that uses the Bronsted-Lowry definition of acids and bases.

But here's my guess, maybe I'm lucky?: Amines are stronger as a base than ammonia, because the alkyl group pushes electrons away towards the nitrogen atom because the nitrogen atom is more electronegative than hydrogen? And the more alkyl groups (such as in secondary and tertiary), the more electrons will be pushed towards the nitrogen atom. So the nitrogen atom is in principle more negatively charged in amines compared to ammonia and in tertiary amines compared to secondary amines. This in turn means that the higher negative charge will lead to a higher attracting forces to hydrogen ions, thus a stronger base

Thanks,

Answer 1

Not so sure that 3º amines are stronger bases than 1º amines.

Your "guess" is pretty much on target, suggesting that the inductive effect of the alkyl group makes the N more negative. But you also should consider stearic hindrance when yo get to the 3º amines. Even though they may have a slightly greater inductive effect compared to 1º and 2º amines, the large, bulky groups can get in the way of a hydrogen trying to bond to the N atom. Clearly, 2º amines are the strongest, but I would tend to classify most 1º amines stronger than most 3º amines. All of them would be stronger than NH3.

These are just my thoughts, and perhaps some others will weigh in with greater insight.