Strength of Nucleophiles

[topdent1]

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Is there a rule of thumb to measure the strength of a nucleophile? I mean how do you tell whether HS- or I- better?

 

[osimsDDS]

Is there a rule of thumb to measure the strength of a nucleophile? I mean how do you tell whether HS- or I- better?

Since no one has answered for a while i will take a shot at this....

A good nucleophile is one that has electrons to give and therefore will attack an electrophile (one in which is lacking electrons and therefore has a strong + charge, take for example a carbonyl group) So I believe a good nucleophile would be something that holds onto its electrons less than that of another molecule...

Your example is HS- which would be an ok nucleophile because the Sulfur atom is bigger than lets say a F atom...or even an oxygen atom

I- atoms are quite and hold onto their electrons loosely because their atomic radii are quite large compared to F or Cl atom

Again im not 100% sure but someone correct me...

 

[Maygyver]

1. stronger base is stronger nucleophile on the same elements. -OH > CH3COO-
2. a nucleophile with a negative charge is stronger than neutral. -OH > H2O
3. basicity increases with nucleophilicity. CH3->NH2->OH->F-
4. smaller size increases nucleophile strength. -OCH3>-OC(CH3)3

 

[DCRedskinsRule]

I don't know the conditions of this rule...but I remember reading somewhere (and it generally makes sense) is that when looking at nucleophiles...the one that is extremely electronegative (I think when the species is neutral) will be a weaker nucleophile than an atom with a lower electronegativity...but again, not 100% sure here

 

[Maygyver]

I don't know the conditions of this rule...but I remember reading somewhere (and it generally makes sense) is that when looking at nucleophiles...the one that is extremely electronegative (I think when the species is neutral) will be a weaker nucleophile than an atom with a lower electronegativity...but again, not 100% sure here

That's the same as the rule 'as basicity increases, nucleophilicity increases' because less electronegative atoms are more basic.