Friday, January 27, 2006

Lecture Summary 1/23: The strength of acids and bases


We considered the molecular underpinnings for what makes an acid or a base strong. Strong acids are very willing to relinquish their protons to water (we are only thinking about aqueous solutions right now). The conjugate bases of strong acids are very weak. We looked at a basicity scale. What makes for a strong or weak base?

Strong bases crave protons:
  • They are small (and so need help in “carrying” their electrons)
  • They are not so electronegative (willing and able to share their electron pair with a proton)
  • They lack resonance stabilization (don’t have any way within the molecule to distribute their electrons, they want the proton to help them have more atoms over which to spread their electrons)

What are the consequences of being a strong base?
  • The conjugate acid will be a weak acid.
  • Strong bases are very effective nucleophiles.
  • Strong bases can effectively displace weaker bases as ligands on metal ions.

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