CHEM 2332H Lecture Notes - Acid Dissociation Constant, Electrophile, Ketone
15 Jul 2014
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Formation & alkylation of enolates pka ~ 20. If add sn2 electrophile: ch3i rates: k[a][ch3i] where k = constant we"ll see a lot of alkoxide sn2 product b/c pka"s are close to each other. Solution: use very strong & non nucleophilic base: There"s a pka difference of 20 from the previous one ---> it"s all going to go to the enolateno ketone left. Ochem page 1 pka~ 16-18 pka > 50. Lda + ketone: deprotonation: quantitative & generally irreversible put in just a bit extra lda to make sure rxn goes to completion. If enolate equilibration by acid/base, unreacted ketone is the most likely acid (in the next problem set!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Can react enolate w/ electrophile in sn2 rxn, a good sn2 electrophile (w/ br or i as leaving group) react on c, not oxygen: lda, 1. 05 equiv, ph-ch2-br. *enolates of esters & amides can also be prepared from lda, and they also do sn2 @ c atom.
