ACS O chem nucleophile question

[alanan84]

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Which is the weakest nucleophile?

A) CH3COONa
B) CH3CH2ONa
C) (CH2CH2)2NLi
D) CF3CH2ONa

The answer is A.

I guess I just don't understand when comparing stuff like this, how do you know which one is stronger and which is weaker?

 

[dfymarine]

Which is the weakest nucleophile?

A) CH3COONa
B) CH3CH2ONa
C) (CH2CH2)2NLi
D) CF3CH2ONa

The answer is A.

I guess I just don't understand when comparing stuff like this, how do you know which one is stronger and which is weaker?

that's easy, look at the answer A, you could tell that it is a carboxylyic acid with a electron density spread over the C=O bond ( like the resonance structure), thus making it more stable and hence it is a weak nucleophile, b/c the charge is stabilized.

whereas I think the strongest nucleophile should be B?????

 

[alanan84]

that's easy, look at the answer A, you could tell that it is a carboxylyic acid with a electron density spread over the C=O bond ( like the resonance structure), thus making it more stable and hence it is a weak nucleophile, b/c the charge is stabilized.

whereas I think the strongest nucleophile should be B?????

Haha, yeah I was just looking at my notes and realized it would be b/c of resonance stabilization.

 

[Philippines03j]

Also if you look at the choices you have two conjugate bases of alcohols. Which are around a PKa of 16. The one with the F has a slightly lower pka/ more acidic because of the Electron Withdrawing Group. The other choice ...NLi is a disubstituded Nitrogen which is going to have even a higher Pka/less acidic. The carboxylic acid is going to have a PKa of around 5 because of the resonance which makes it the strongest acid or weakest nucleophile. It is a good idea to be very familiar with the PKA chart. Even in questions that dont directly ask about Pka it will come in handy.

Forgot to say the Pka of the (Ch3Ch2)2NH has a PKA of 36. This is very strong it is the structure of LDA.