# Reaction of vinylacetylene (but-1-en-3-yne) with HCl

Vinylacetylene contains both a double bond and a triple bond. We know that alkenes are more reactive to electrophillic addition reactions, so I thought that the $$\ce{H+}$$ from $$\ce{HCl}$$ would get abstracted via the double bond. However, the final answer says the product is 2-chloroprene, which is possible only if the triple bond abstracts it.

My teacher said that it was because of the carbocation stability and the abstraction of $$\ce{H+}$$ by triple bond forms a stabler carbocation and leads to conjugation and hence is favoured.

But then Wikipedia says that a 1,4 addition takes place and an allene rearrangement takes place.This means that the triple bond is the one that reacts first , but in a 1,4 fashion to form an allene which then rearranges. I was unable to find a mechanism for this allene rearrangement, why is this 1,4 addition favoured, and why it takes place. Also, what is the correct explanation: the first one or the second one?

• The allene rearrangement is catalysed by CuCl May 4 '20 at 9:05
• @Waylander. Yes but how does the rearrangement happen? Also is the explanation given by my teacher correct? He does not talk about this rearrangement at all. May 5 '20 at 3:27