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Assume a tetrahedral carbon with a leaving group reacts via the SN1 mechanism. This carbon is initially sp3 hybridized, and after the departure of the leaving group, the resulting tertiary carbocation is sp2 hybridized with an empty p orbital. My understanding of why this carbocation has an empty p orbital instead of an empty sp3 orbital is that the carbocation's 3 valence electrons "rehybridize" into 3 sp2 orbitals, leaving an empty p orbital behind. I believe this occurs because sp2 orbitals are more stable than sp3 orbitals since orbitals with more s character are lower in energy. However, I just learned that the solvolysis of vinyl halides yields a carbocation with an empty sp2 orbital (https://chemistry.stackexchange.com/a/14483). Based on my understanding of tertiary carbocations, this vinylic carbocation would "rehybridize" into 2 sp orbitals, nothing would happen to its filled p orbital, and it would leave behind another empty p orbital. Therefore, I've concluded that my understanding of "rehybridization" must be wrong. Can someone help me understand what's actually going on in terms of orbitals during the formation of carbocations?

Clarification: If I wasn't completely clear, my main question is why vinylic carbocations have an empty sp2 orbital while tertiary carbocations have an empty p orbital. I think my problem here is that I have a misunderstanding of "rehybridization" during the formation of a carbocation that I explain above.

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  • $\begingroup$ chemistry.stackexchange.com/questions/78672/… $\endgroup$
    – Mithoron
    Commented Oct 31, 2023 at 1:24
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    $\begingroup$ Does this answer your question? Do vinyl cations adopt a classical or non-classical structure? $\endgroup$
    – Mithoron
    Commented Oct 31, 2023 at 1:25
  • $\begingroup$ @Mithoron Thanks for these. However, they don't necessarily answer my primary question of why vinyl carbocations have an empty sp2 orbital while tertiary carbocations have an empty p orbital. $\endgroup$
    – allen.ch36
    Commented Oct 31, 2023 at 2:02
  • $\begingroup$ Answers that ron wasn't right this time. Your thinking was better, but you still didn't foresee it could be non-classical instead of linear. $\endgroup$
    – Mithoron
    Commented Oct 31, 2023 at 12:56

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