hyperconjugation

[fatima....@gmail.com]

How in what way hyperconjuagtion is helpful in bringing out the stability of carbocation??

[arnab...@gmail.com]

On Wednesday, August 7, 2013 7:05:29 PM UTC-6, fatima....@gmail.com wrote:
> How in what way hyperconjuagtion is helpful in bringing out the stability of carbocation??

Hi Fatima,

If you see this link: http://padakshep.org/otp/subjects/chemistry/organic-chemistry/steric-electronic-effects/#Hyperconjugation , the chemical species on the right hand side of the second chemical equation under hyperconjugation section shows a neutral alkene compound and a proton. Therefore, the positive charge on the carbon has been neutralized which brings it down from high energy positively charged state. That is why it says that the carbocation is stabilized. BUT this is just a temporary relief for the compound...it does not remain in that state for long... the more this happens, the more it will be stabilized... so hyperconjugation is a good thing to bring stability.

[saurjadg]

IM pasting my reply to ur email. just so that other people can participate.
So a tertiary carbocation is more stable than a primary, this is because of inductive effect (+I effect) where the three methyl groups push electron to the positive (electron poor) C center thus stabilizing it. As tertiary cations have three Cs pushing electron and primary has none, tert is more stable than primary, I hope I made myself clear here.
But remember hyperconjugation always needs a network of sigma and pi bonds to operate...so in cases where we have a conjugated electron system and a methyl group which can form hyperconjugative structures with it, a methyl group has a more stabilizing effect than a trimethyl for eg

 (A) (CH3)3-C-CH=CH-CH2+ and (B) H-CH2-CH=CH-CH2+...

B can take part in hyperconjugation because the underlined boldfaced H -C bond electrons can conjugate with the double bond and the negative charge...this is not possible in A as there are no C-H sigma bonds which can conjugate with the double bond.