Secondary carbanion less stable than primary?

Question

I know carbocation stability proceeds tert>sec>prim, but does that mean carbanions are opposite?

one more detail. My problem is showing a butane with a lone pair on the second carbon. I have to compare relative stabilities with a CH2 substituent on a cyclohexane. I need to know WHY one or the other is less stable.

Thanks first guy, that is what I put, I just wanted to be sure.

Answer 1

Yes, carbanions have a -ve charge unlike the +ve charge in carcocations.

The cyclohexane one (radical) is more stable since more resonance structures are possible.

Answer 2

Figure that the stability of a carbanion is determined by
1) inductive effect. Electronegative atoms adjacent to the charge will stabilise the charge.
2) hybridisation of the charge-bearing atom. The greater the s-character of the charge -bearing atom, the more stable is the anion
3) The extent of conjugation of the anion. Resonance effect can stabilise the anion

Answer 3

carbanion is an intermediate formed in Grignard rxn or organometalllic rxn...they work by SN2 mechanism which prefers as you know primary alkyl halide groups and they do not like tertiary or bulkyl groups at all because of steric hindrances. Tertiary prevents the nucleohphile from attacking the right carbon.