[orgo814]

I'm comparing the nucleophilicity values (from swain scott eqn) and the values increase from CH3CO2-, PhO-, and CH3O-. I understand that CH3 would be electron donating and there isn't resonance effect so that would be the strongest nucleophile. That makes sense to me.

However, comparing CH3CO2- and PhO-, they are both stabilized by resonance. So, why is PhO- a stronger nucleophile than CH3CO2? And if looking at the amines (pyridine, aniline, and (Et)3N, why is pyridine less nucleophilic than aniline?)

Thanns

[Babcock_Hall]

How are nucleophilicity and basicity correlated?

[Kate]

I'm jumping in, because this is something that has confused me for a while. Supposedly, nucleophilicity and basicity are strongly correlated, but they're not the same. Basicity is easy to check through pka values, with strong bases having higher pka values. Nuclephilicity, from my understanding, also takes into account the volume of the nucleophile and the steric effects it might produce in a particular reaction.

In the examples above, the negative charge is more stabilized in CH3COO- than in PhO-, because of the aromaticity of the latter. CH3O- is the better nucleophile because its negative charge is less stabilized (no electron-withdrawing groups other than O and no ressonance possibility, plus the methyl group is electron-donating) and the ion is relatively small. The same logic applies to the nitrogen series.

[Babcock_Hall]

Obviously I agree that sterics are important when assessing nucleophilicity, but if we hold steric bulk constant and change basicity, then nucleophilicity will change in the same direction.  Ditto for polarizability.

[chaosified]

I'm jumping in, because this is something that has confused me for a while. Supposedly, nucleophilicity and basicity are strongly correlated, but they're not the same. Basicity is easy to check through pka values, with strong bases having higher pka values. Nuclephilicity, from my understanding, also takes into account the volume of the nucleophile and the steric effects it might produce in a particular reaction.

In the examples above, the negative charge is more stabilized in CH3COO- than in PhO-, because of the aromaticity of the latter. CH3O- is the better nucleophile because its negative charge is less stabilized (no electron-withdrawing groups other than O and no ressonance possibility, plus the methyl group is electron-donating) and the ion is relatively small. The same logic applies to the nitrogen series.

IMO, the best way to put it is Nucleophilicity is a kinetic property, basicity is a thermodynamic property. In both cases though, solvent plays a big role.