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In the reaction CH3-CH2-Li + ethyne

Do the lithium and a hydrogen from ethyne just switch places? And how would i draw the curved arrow notation for this? I'm assuming from the C-Li bond in one to the C-H bond in the other and vice versa? Will upload a pic of my attempt when I get home.

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  • $\begingroup$ It would be quite difficult to make exact mechanism here, alkyllithiums are oligomers and would react via intermediate pi-complexes. $\endgroup$
    – Mithoron
    Commented Sep 28, 2017 at 14:34

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Terminal alkynes are weak acids, but they are still stronger ones than alkenes and alkanes. This actually means they would readily react with conjugate bases of weaker acids, giving them the proton. So yes, since ethyne is a stronger acid than ethane (and ethyl anion is a stronger base than ethynyl anion - the list for bases is reverse due to obvious reasons), they will exchange H and Li.

Below you can see a mechanism I would use to describe the problem in your question. C-Li bond has significant contribution of both covalent and ionic components, so I wrote it as both in equilibrium: enter image description here

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    $\begingroup$ >Terminal alkynes are weak acids, but they are still stronger ones than alkenes and alkanes. || A lot stronger than alkenes and alkanes, I'd say. You can create enough deprotonated alkyne with KOH in non-aqueous media for it to work as intermidiate in many reactions. No so luck with alkanes and alkynes. $\endgroup$
    – permeakra
    Commented Sep 28, 2017 at 10:06
  • $\begingroup$ Unless the "alkene" is cyclopentadiene, maybe? $\endgroup$
    – Oscar Lanzi
    Commented Sep 28, 2017 at 14:41
  • $\begingroup$ Calling cp an alkene is like calling DNA an alcohol, because come on, it has OH group in deoxyribose fragment. $\endgroup$
    – MEL Science
    Commented Sep 28, 2017 at 20:03

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