[scienceguy]

If an acid is strong, is its conjugate base a strong nucleophile or a weak nucleophile? Is there a correlation between acid strength and nucleophylicity?

[Dan]

If an acid is strong, is its conjugate base a strong nucleophile or a weak nucleophile?

First, will the conjugate base be a weak base or a strong base?

Is there a correlation between acid strength and nucleophylicity?

The question really is whether basicity correlates with nucleophilicity. Think about what you already know:

Can you think of any poorly nucleophilic strong bases?
Can you think of any good nucleophiles that are only very weakly basic?

[scienceguy]

Water (thinking of the hydronium ion as a conjugate acid) is a poorly nucleophylic weak base.

I can't think of any poorly nucleophylic strong bases.

I can't think of any good nucleophiles that are only very weakly basic.

I guess that answers my question.

I mainly wanted to know if the conjugate base of sulfuric acid would be a good nucleophile. It seems it would not. The conjugate base is stabilized by resonance, also.

[Dan]

I can't think of any poorly nucleophylic strong bases.

I can't think of any good nucleophiles that are only very weakly basic.

I guess that answers my question.

Unfortunately not, think again!

Example of a poorly nucleophilic strong base: LDA
Example of a good nucleophile that is a weak base: iodide

See if you can think of others.

Nucleophilicity does not necessarily parallel basicity, other factors such as polarisability and sterics are important.

[Babcock_Hall]

When compared with each other in basicity and nucleophilicity, phenoxide and thiophenoxide make a good pair for illustrating that the two properties do not move in lock step with each other.

[scienceguy]

Thanks for the responses!

So do either of you know off hand if the conjugate base of sulfuric acid is a strong nucleophile?

[scienceguy]

I went to the library. I found what I needed in March's Advanced Organic Chemistry (2007), pg. 494.

For attacking carbonyl carbons (what I was looking for), nucleophilicity follows basicity somewhat closely.