Addition of HBr twice to alkynes to give geminal dibromides

by James

Description: Addition of two equivalents of hydrogen bromide (HBr) to alkynes results in geminal dibromides. Content available for Reactionguide members only. Not a member? Get access for about 30 cents / day!

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Ian Hunt January 26, 2012 at 1:18 am

Hmmm… a couple of concerns here…. first vinyl carbocations are quite unstable and I think they should (if formed) rearrange to allyl cations which would be much more stable. I recall reading that there are no known examples of rearrangements…. thus the implication would be that the vinyl cation is not formed. Many texts tend to show a concerted process with 2 HX involved (which is supported by termolecular kinetics.

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