explain the stability 0f carbocations with the concept of hyperconjugation
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hey friend here is your answer^^
we know that greater the number of alpha H, greater is the stability of carbocation.
But consider this:
CH3CH2+CHX3CHX2X+ and. CH3CH2CH2+CHX3CHX2CHX2X+
The first one has 3 alpha H while the second one has 2. So first one is more stable, as our teachers say. But even C-C sigma bond can participate in hyperconjugation, isn't it?
Going with that, second one has equal no bond resonating structures and even higher inductive effect of ethyl group. So second one should be more stable (without overruling the dominance of hyperconjugation).
Stability of carbocations
If we now consider the various types of cation, we should be able to rationalise the order of stability.
The methyl group is completely unstabilised through hyperconjugation, due to the stereoelectronic requirement that the σ bond be located on the adjacant carbon (of which the methyl cation has none).
Primary carbocations have a maximum of 3 σ-bonds capable of hyperconjugation, secondary a maximum of 6, tertiary a maximum of 9– hence why the tertiary is the most stable cation out of the simply alkyl groups (the allyl and benzyl systems in the diagram 1above are stabilised through delocalisation of the charge onto the pi system).
Going back to your question of ethyl vs propyl carbocations, you can hopefully now see that they have the same number of σ-bonds in the correct position to participate in hyperconjugation.
have a nice day ...~~
we know that greater the number of alpha H, greater is the stability of carbocation.
But consider this:
CH3CH2+CHX3CHX2X+ and. CH3CH2CH2+CHX3CHX2CHX2X+
The first one has 3 alpha H while the second one has 2. So first one is more stable, as our teachers say. But even C-C sigma bond can participate in hyperconjugation, isn't it?
Going with that, second one has equal no bond resonating structures and even higher inductive effect of ethyl group. So second one should be more stable (without overruling the dominance of hyperconjugation).
Stability of carbocations
If we now consider the various types of cation, we should be able to rationalise the order of stability.
The methyl group is completely unstabilised through hyperconjugation, due to the stereoelectronic requirement that the σ bond be located on the adjacant carbon (of which the methyl cation has none).
Primary carbocations have a maximum of 3 σ-bonds capable of hyperconjugation, secondary a maximum of 6, tertiary a maximum of 9– hence why the tertiary is the most stable cation out of the simply alkyl groups (the allyl and benzyl systems in the diagram 1above are stabilised through delocalisation of the charge onto the pi system).
Going back to your question of ethyl vs propyl carbocations, you can hopefully now see that they have the same number of σ-bonds in the correct position to participate in hyperconjugation.
have a nice day ...~~
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