How to determine the most stable carbanion?

[JMC117]

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I'm not sure that I understand how to do this. I've looked everywhere for more clarification. I know for carbocation it's 3>2>1>CH3. Does anyone know? Thanks in advance!

 

[Vicviper]

http://www.chem.wisc.edu/areas/reich/chem842/_chem842-01-intro%7B03%7D.htm

Check out that site, it's got some nice info. If I remember correctly, carbanion stability is based on similar factors to carbocation stability, like conjugation, inductive effects, and electronegativity of surrounding atoms.

 

[oreoeater82]

i think the stability of carbanions are just the opposite of carbocations... namely:

Me>1>2>3

I could be wrong though.

http://www.britannica.com/EBchecked/topic/94652/carbanion/1110/Reactions

read this about 3/4 of the way down and it will explain it👍

 

[Vicviper]

Oh, haha, yeah, that's what I meant! =p Haha, I meant to add in that they use similar factors, but have the opposite effects ... I think!

 

[JMC117]

oh ok, well that was easy enough thanks!

i hope you don't mind if i ask another question. should this be SN2 or E2? just to clarify, the answer is E2 but shouldn't it be SN2 because the strong base (OH) is small?

 

[tdkyun]

oh ok, well that was easy enough thanks!

i hope you don't mind if i ask another question. should this be SN2 or E2? just to clarify, the answer is E2 but shouldn't it be SN2 because the strong base (OH) is small?

I think both reactions are possible but the question specifically asks for the major product for elimination reaction

 

[JMC117]

Thanks for answering! I figured both were possible.

 

[oreoeater82]

as you probably are already aware... Sn2 and E2 reactions can occur simultaneously. E2 reactions are favored over Sn2 with the type of reaction conditions shown in this problem.

 

[Broncos85]

If it was a big bulky base like t-butoxide or LDA, instead of KOH, it would be E2 hoffman product. In addition, if the molecule was a primary halide with the KOH (strong small base), then it would be an SN2.