I am trying to self learn solomon's organic chemistry book, but there is no explanation over why we should use THF in oxymercuration. After a quick search I found out that THF help stabilize in hydroboration, but is it the same for oxymercuration? and I still don't understand why and how THF can help stabilize in hydroboration.

  • $\begingroup$ It's the solvent. $\endgroup$
    – Zhe
    Aug 15, 2019 at 13:39

1 Answer 1


$\ce{THF}$ is a polar aprotic solvent, that is, it can stabilize positive charges but not negative ones since it won't form hydrogen bonds with the help of any of its own hydrogen atoms.

Thus the carbocationic intermediate, that is the mercurinium ion is still stabilized, allowing the reaction to proceed.

And in Hydroboration, $\ce{THF}$ acts as the solvent as well but plays the additional role of shifting the equilibrium between diborane and borane to the side of the latter. As you might know, the Boron atom of $\ce{BH3}$ is electron deficient, which plays a key role in the formation of the trialkylborane intermediate of the Hydroboration reaction. Formation of diborane quenches this electron deficiency of borane by the formation of two 3-centred, 2-electron bonds in the dimer.

  • $\begingroup$ so without THF, the mercurinium ion will be reactive and won't react as intended pathway? $\endgroup$
    – AegisNine
    Aug 16, 2019 at 11:22
  • 1
    $\begingroup$ @AegisNine It won't necessary be reactive but the lowering of energy of an intermediate is always desirable. It will solvate the intermediate. $\endgroup$ Aug 16, 2019 at 12:16
  • 1
    $\begingroup$ @FᴀʀʜᴀɴAɴᴀᴍ, What if we use a polar protic solvent? It still stabilises the mercurinium ion right. $\endgroup$
    – Vishnu
    Sep 22, 2019 at 12:20
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    $\begingroup$ @Intellex Yes. Only anionic intermediates are destabilized as such by solvent effects and that is in the case of a polar aprotic solvent. $\endgroup$ Sep 22, 2019 at 12:22

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