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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: orgo814 on October 16, 2012, 02:57:09 AM

Title: nucleophilicity
Post by: orgo814 on October 16, 2012, 02:57:09 AM: Why is CH3CO2H a better nucleophile than CH3OH?

Is it because the charge is more dispersed between the two oxygens in the first molecule making it more basic?

I'm having trouble with nucleophilicity so any good links would help too
Title: Re: nucleophilicity
Post by: discodermolide on October 16, 2012, 03:05:33 AM: Acetic acid is a weak nucleophile, and it is not basic. Methanol is also a weak nucleophile.
If you talk about their respective anions them methoxide is a stronger nucleophile than acetate but both of them are reasonable nucleophiles.
Have a look at this page:
http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch08/ch8-5.html (http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch08/ch8-5.html)
and here
http://chemwiki.ucdavis.edu/Organic_Chemistry/Virtual_Textbook_of_OChem/Alkyl_Halides/Alkyl_Halide_Reactions/Substitution_and_Elimination_Reactions_of_Alkyl_Halides/SN1_Substitution_Reactions/Nucleophilicity_and_Solvent_Effects (http://chemwiki.ucdavis.edu/Organic_Chemistry/Virtual_Textbook_of_OChem/Alkyl_Halides/Alkyl_Halide_Reactions/Substitution_and_Elimination_Reactions_of_Alkyl_Halides/SN1_Substitution_Reactions/Nucleophilicity_and_Solvent_Effects)
Title: Re: nucleophilicity
Post by: orgo814 on October 16, 2012, 03:11:12 AM: ok thanks but not looking at their respected anions, how would I know whether acetic acid or methanol is a better nucleophile?
Title: Re: nucleophilicity
Post by: discodermolide on October 16, 2012, 03:23:07 AM: Look at the table in the first link I posted.
Title: Re: nucleophilicity
Post by: orgopete on October 16, 2012, 08:13:37 PM: Is CH3COOH a better nucleophile than CH3OH?
Title: Re: nucleophilicity
Post by: orgo814 on October 22, 2012, 01:09:03 PM: The table is saying that CH3CO2H is a very weak nucleophile and CH3OH is a weak nucleophile. So, is my textbook wrong for saying CH3CO2H is a better nucleophile?
Title: Re: nucleophilicity
Post by: PhDoc on October 23, 2012, 01:52:17 AM: What are the better nucleophiles of the pairs?
1. CH3CO2H vs CH3CS2H
2. CH3S(O)CH3 vs CH3SCH3
3. CH3NH2 vs CH3C(O)NH2

What makes something a good nucleophile?
Title: Re: nucleophilicity
Post by: orgopete on October 23, 2012, 11:43:17 PM: Quote from: butlerw2 on October 22, 2012, 01:09:03 PM
The table is saying that CH3CO2H is a very weak nucleophile and CH3OH is a weak nucleophile. So, is my textbook wrong for saying CH3CO2H is a better nucleophile?

I think everyone will agree with your textbook. Try replacing the word weak with poor. I think you have switched the nucleophilicity. An sp2 hybridization is more electron withdrawing than sp3. That effect probably alters the nucleophilicity and acidity.
Title: Re: nucleophilicity
Post by: orgo814 on October 24, 2012, 08:13:08 PM: so the carbonyl group with the electron withdrawing effect makes it a better nucleophile?
Title: Re: nucleophilicity
Post by: orgopete on October 26, 2012, 01:00:52 AM: Quote from: butlerw2 on October 22, 2012, 01:09:03 PM
The table is saying that CH3CO2H is a very weak nucleophile and CH3OH is a weak nucleophile. …

Language problem?
As nucleophiles, CH3OH(weak)>CH3CO2H(very weak)
I reason the sp2 oxygen is electron withdrawing and reduces donation of non-bonded electrons of CH3CO2H's OH group. This would also increase acidity of CH3CO2H compared to CH3OH.