I still distinctly remember reading about how Lewis acidity/basicity was characterized using kinetics. The reason given was that because formation constants are so large, these reactions are not equilibrium reactions and completion reactions. So we just characterize strength using the rate of reaction/formation. This at least makes partial sense; formation constants are huge:


EDIT: I have found what I read:

Many reactions of nucleophiles are not reversible. A bond forms, a bond breaks, and that’s the end of the reaction. The problem with this from a measurement standpoint is that we often can’t determine an equilibrium constant for a reaction. And if we can’t do that, then we can’t develop a reactivity scale based on equilibria.

If we can’t measure equilibria, then what do we do? Well, we use the next best measurement available: to measure reaction rates.

1) Does the quoted text make sense?

2) Am I interpreting it correctly or out of context?

3) Reference to previously answered question: Lewis base strength and the hydrogen proton


1 Answer 1


I think I got this figured out.

Acidity and basicity are thermodynamic properties.

Nucleophilicity/electrophilicity are kinetic properties.

Lewis acids are electrophiles.

Lewis bases are nucleophiles.

We can use electrophile/nucleophile in describing Lewis acids/bases. But care should be taken to ensure we don't conflate kinetics with thermodynamics.

I think I finally got this issue resolved.

  • $\begingroup$ Nice job solving your own issue. $\endgroup$
    – Lighthart
    Jul 14, 2014 at 14:36

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