My understanding is that in alkyl-substituted alkenes there is hyperconjugation between $𝜎(\ce{C−X})$ and $𝜋^∗(\ce{C=C})$. I also have read that more alkyl-substituted alkenes are many folds more reactive in addition reactions. I understand how hyperconjugation stabilizes alkyl-substituted carbocations.

However, based on the fact that alkyl-substituted alkenes are more "stable", and the fact that the hyperconjugation between their $𝜎(\ce{C−X})$ and $𝜋^∗(\ce{C=C})$ causing a delocalization of electrons at the $\ce{C=C}$ double bond, wouldn't the alkyl-substituted alkene be less reactive? Obviously stability comes into play, and additionally the loss of electron density at the $\ce{C=C}$ double bond should mean that the $𝜋$ bond is less of a nucleophile so would prevent attraction of electrophilic addition.

One way I came up to justify this is maybe that the stability from the hyperconjugation of the carbocation outweighs stability from hyperconjugation of alkene. Or that somehow the hyperconjugation between $σ(\ce{C-X})$ and $π^∗(\ce{C=C})$ adds electron density to the $𝜋^∗$ making it more attractive to electrophiles that can break the $\ce{C=C}$ double bond. Of course, I am only using these as justifications to fill in misunderstandings.


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