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The reaction of a terminal alkyne with $\ce{NaNH2}$ leads to the loss of hydrogen ion from the terminal carbon.

But what will happen if the alkyne is a non-terminal one? How would $\ce{NH2-}$ attack then? Would any reaction even happen?

As an example, what would happen in case of this following reaction:

$$\ce{H3C-C#C-CH3 + NaNH2 ->[\text{liq.}~NH3] ?}$$

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  • $\begingroup$ I don't believe if any major reaction would take place. This species isn't acidic enough. $\endgroup$ Commented Apr 19, 2021 at 11:56
  • $\begingroup$ One of the questions I did asked which of the following compounds would give optically inactive compounds with the set of reagents I gave above, and this was one of the options. It had marked this option as one of the correct ones. So essentially there is no reaction taking place and the product will have the same stereochemistry as the original reactant right? This is what I thought so, a reaction didn't seem reasonable $\endgroup$
    – Ashish
    Commented Apr 19, 2021 at 12:01
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    $\begingroup$ The answer depends upon the conditions of the reaction. In the presence of NH3 as solvent it is unlikely that alkyle-allene-alkyne isomerization will occur. Under the correct conditions the propargylic hydrogen is acidic enough for NaNH2 to form the anion reversibly and in low concentration and effect isomerization to the allene and ultimately to the anion of but-1-yne. This zipper reaction is a variant of the Varrentrapp reaction. ursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/Varrentrapp/… $\endgroup$
    – user55119
    Commented Apr 19, 2021 at 14:22
  • $\begingroup$ @NilayGhosh thanks! Seems like a possible dupe, I'll close this question once I confirm the answer $\endgroup$
    – Ashish
    Commented May 5, 2021 at 5:19
  • $\begingroup$ @user55119 possibly that is so the case. How does $\ce{NH3}$ as a solvent affect it though ? $\endgroup$
    – Ashish
    Commented May 5, 2021 at 5:21

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