Asked by ny
Which base(s) is weaker than ammonia?
Strengths of Acids and of Bases
Ammonia
Hydroxylamine
Pyridine
Methylamine
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Hydroxylamine and pyridine are weaker bases than ammonia.
Approximate pKa values of the conjugate acids (lower pKa = weaker base):
- CH3NH3+ (methylammonium): ≈ 10.6 (methylamine is stronger than NH3)
- NH4+ (ammonium): ≈ 9.25
- NH3OH+ (hydroxylammonium): ≈ 5.9
- C5H5NH+ (pyridinium): ≈ 5.25
Reasons:
- Methylamine is stronger than ammonia because the alkyl group is electron‑donating.
- Hydroxylamine is weaker because the electronegative O withdraws electron density from the nitrogen, reducing its basicity.
- Pyridine is weaker because the lone pair on the ring N is in an sp2 orbital and the aromatic system/delocalization makes it less available for protonation.
Approximate pKa values of the conjugate acids (lower pKa = weaker base):
- CH3NH3+ (methylammonium): ≈ 10.6 (methylamine is stronger than NH3)
- NH4+ (ammonium): ≈ 9.25
- NH3OH+ (hydroxylammonium): ≈ 5.9
- C5H5NH+ (pyridinium): ≈ 5.25
Reasons:
- Methylamine is stronger than ammonia because the alkyl group is electron‑donating.
- Hydroxylamine is weaker because the electronegative O withdraws electron density from the nitrogen, reducing its basicity.
- Pyridine is weaker because the lone pair on the ring N is in an sp2 orbital and the aromatic system/delocalization makes it less available for protonation.
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