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There is a specific part of the biosynthesis of terpenes that makes me confused:

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According to this mechanism, the double bond of the isopentenyl pyrophosphate attacks the primary carbocation, when it would make more sense to attack the tertiary carbocation that could be formed by resonance. Am I missing something here? Clearly, this is not a concerted process if the mechanism is displayed in this way, and an intramolecular resonance conversion would be faster than a nucleophilic attack.

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    $\begingroup$ There is only one carbocation! There is no "resonance conversion" between two distinct carbocations, one primary and one tertiary. Resonance forms do not interconvert! Anyway, the regioselectivity is probably enzyme-controlled. $\endgroup$ – orthocresol Dec 29 '17 at 18:53
  • $\begingroup$ Yeah, sorry about that. I was trying to make a point though. $\endgroup$ – phi2k Dec 29 '17 at 23:23
  • $\begingroup$ Enzyme-controlled and helped by sterics (it’s easier to attack the primary position than the tertiary one). $\endgroup$ – Jan Dec 30 '17 at 17:00

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