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Suppose we take these two compounds:

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The first carbocation can rearrange to produce the second one by hydride shift. Which is more stable ? Why ?

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    $\begingroup$ The compound to the left seems like a carbonyl in disguise. How did you get there? $\endgroup$
    – Variax
    Dec 29 '16 at 9:33
  • $\begingroup$ @Variax Hydride shift. $\endgroup$ Dec 29 '16 at 9:37
  • $\begingroup$ @Variax chem.libretexts.org/Reference/Organic_Chemistry_Glossary/… $\endgroup$ Dec 29 '16 at 9:37
  • $\begingroup$ What I meant is how did you obtain the first carbocation in the first place? $\endgroup$
    – Variax
    Dec 29 '16 at 9:55
  • $\begingroup$ By heating a diol with concentrated sulfuric acid and then a hydride shift. I don't think it matters how I got the carbocations. I just want to compare the relative stabilities of the two interconvertible structures. $\endgroup$ Dec 29 '16 at 10:09
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I am inclined to consider the second one as a "bona-fide" carbocation, if that makes sense. The first one resembles a protonated aldehyde rather than a carbocation, so relatively speaking, the first one should be more "stable".

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  • $\begingroup$ The question deserves a more thorough answer than ‘I think’. $\endgroup$
    – Jan
    Dec 29 '16 at 23:36

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