Formation and Reactions Part 1 The CC bonds of a molecule under construction constitute its scaffolding Reactions which form new CC bonds are exceptionally useful synthetically SN2 reactions which use a ID: 288581
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Slide1
Carbanions
:
Formation and Reactions
Part 1Slide2
The C-C bonds of a molecule under construction constitute its scaffolding. Reactions which form new C-C bonds are exceptionally useful synthetically. SN2 reactions, which use a
carbanion
as a nucleophile represent one solution to this problem.Slide3
General Types of
CarbanionsSlide4
Formation of Stabilized
Carbanions
Note that, for this reaction to succeed, the
carbanion
must be a weaker base than the base employed to
deprotonate
its conjugate acid.Slide5
Bases often used to form (stabilized)
carbanions
Increasing
BasicitySlide6
Formation of
Alkynyl
Anions(can be formed by deprotonation)Slide7
AlkynesSlide8Slide9Slide10Slide11Slide12
Reactions of
Alkynyl
AnionsSlide13Slide14Slide15Slide16Slide17Slide18Slide19Slide20Slide21Slide22Slide23Slide24Slide25Slide26Slide27Slide28Slide29
Other
Carbanions
Formed by Deprotonation(Enolate Anions)Slide30Slide31Slide32Slide33Slide34Slide35Slide36
Grignard and
Organolithium
Species(Unstabilized Carbanions)Slide37
Formation of
Organometallics
by Reaction of Organohalides with Magnesium and Lithium MetalSlide38Slide39Slide40Slide41Slide42Slide43Slide44Slide45Slide46Slide47Slide48
Formation of
Carbanions
by Halogen-Metal Exchange Reactions
This works when R’-M is a more stable
organometallic
(
carbanion
) than R-M.
This reaction is often used to form vinyl- and aryl-
carbanions
, where the sp
2
hybridized orbital has more ‘s-character’ than the starting sp
3
hybridized orbital.Slide49Slide50
Formation of
Organometallics
by Halogen-Metal ExchangeSlide51Slide52Slide53Slide54
Reactions of
Organomagnesium
and Organolithium SpeciesSlide55Slide56Slide57Slide58Slide59Slide60Slide61Slide62Slide63Slide64Slide65Slide66Slide67Slide68Slide69Slide70Slide71Slide72