Do E2 elimination reactions occur in alkenes? If not, what mechanism is used?

If they do, are they limited by any stereochemical rules as alkanes do (antiperiplanar)?

My question is pernitent to the alkyne reaction mechanism, where both the E and Z alkenes undergo elimination to form the alkyne.enter image description here

My guess is E2 mechanism is possible for the Z alkene, while the E alkene undergoes E1


1 Answer 1


No E1elimination. E2 in both cases. The E-isomer has a good overlap; syn elimination. The Z-isomer goes through anti elimination.

  • $\begingroup$ Thank you. I am guessing no E1 due to the instability of a vinylic carbocation But I have never heard of syn elimination before Are there any resources you'd recommend? $\endgroup$
    – Diracc
    Commented Nov 29, 2017 at 5:48
  • $\begingroup$ You are right about the carbocation. For syn elimination in vinyl halides, See chemistry.stackexchange.com/questions/23966/… $\endgroup$
    – user55119
    Commented Nov 29, 2017 at 16:11

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