Nucleophilicity and Basicity
- Thread starter Andre3k
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Check out the acids...Like Halogens...Cl- will not touch a Hydrogen but is a decent nucleophile.
CN- is also a good nucleophile and HCN is somewhat of a strong acid.
Good question, this always annoyed me but these examples should help you understand this concept.
CN- is also a good nucleophile and HCN is somewhat of a strong acid.
Good question, this always annoyed me but these examples should help you understand this concept.
Why wont Cl- touch a proton? Since when?
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I don't mean it literally...I mean HCl is a strong acid and full dissociates in water. Basically saying that Cl- is an EXTREMELY weak base.
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Not a great nucleophile, but a decent one.
As for CN-:
CN- is a strong nucleophile and a weak base I think.
Daaaamn, good question!! At first I wanted to say that when basicity and nucleophilicity do not correlate, then it is usually a matter of sterics. For example, imagine a lone pair of electons on a big bulky molecule. It might be able to pick up some H's in solution or pluck an H off the other substrate (acid), but it's too bulky to attack an electrophilic site. So it would be a good base but poor nucleophile. I think one example - although maybe not a good one - is pyrimidine. It has a lone pair that you could consider more restrained from nuc attack by that bulky ring, compared with a more simple nuc like CH3O-. Pyrimidine can still pluck H's off of other molecules, making it a decent base. (My orgo prof used this example for one lecture.. 'pluck' was his term too, not mine, heh)
And I might be completely wrong on all this sterics stuff. It's been a while for me.
But there are some good websites that explain that the difference lies between thermo and kinetic control, and substitution vs elimination. Maybe this makes more sense?
-Nucleophilic attack is a kinectic controlled situation, where the lone pair attacks the carbon/electrophile. Think substitution SN1 SN2 rxns.
-A base reaction occurs under thermodynamic control, when the lone pair attacks a proton. Think elimination E1 and E2 rxns.
http://courses.cvcc.vccs.edu/CHM_Bowman/Lecture Notes Ch 8 Nucleophilicity.doc
http://www.chem.ucalgary.ca/courses/351/Carey/Ch08/ch8-6.html
meh??? awesome question. Does the dat get into these kind of details?
