1. Amines act as bases because the nitrogen lone pair captures a proton.
2. Basicity is measured by the pKaH — the pKa of the protonated ammonium ion.
3. Alkyl amines are more basic than ammonia because alkyl groups donate electron density.
4. Aniline is a much weaker base because its lone pair delocalizes into the benzene ring.
5. Amides are essentially non-basic because the lone pair is locked in resonance with the carbonyl.
6. Summary
Amines = organic bases · rank by pKaH (higher = stronger) · alkyl amines ~10.6 > ammonia ~9.3 · aniline ~4.6 and amides ~0 are weak because resonance removes the lone pair · pyridine ~5.2 is modest.
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Methylamine. A higher pKaH means the conjugate acid holds its proton more tightly, so the amine is the stronger base — the methyl group donates electron density and stabilizes the ammonium ion.
Aniline's nitrogen lone pair is delocalized into the benzene ring by resonance, so it is less available to grab a proton, making aniline a much weaker base.
The nitrogen lone pair is tied up in resonance with the adjacent carbonyl (C=O), leaving it unavailable to accept a proton — so the pKaH sits near 0 to −1.
Methylamine (~10.6) > ammonia (~9.3) > aniline (~4.6) > acetamide (~0). Electron-donating alkyl groups raise basicity; resonance delocalization lowers it.
Draw this on the whiteboard
Open the OChem Board whiteboard — benzene rings, wedge/dash bonds, and a clickable periodic table built in. No account needed.