The reaction between propyne CHCCH and hydrogen chloride HCl is an electrophilic addition reaction. The mechanism involves the following steps:1. Protonation of the alkyne: The electrophilic hydrogen atom from HCl is attracted to the electron-rich triple bond of propyne. The triple bond acts as a nucleophile and attacks the hydrogen atom, forming a bond with it. This results in the formation of a carbocation intermediate and a chloride ion Cl .CHCCH + HCl CHCCH + Cl2. Attack of the nucleophile: The carbocation intermediate is electron-deficient and positively charged. The chloride ion Cl , which is a good nucleophile, attacks the carbocation, forming a bond with the carbon atom.CHCCH + Cl CHCClH=CHThe product obtained is 1-chloro-2-propene also known as 1-chloropropene or allyl chloride , which is a vinyl chloride compound with the molecular formula CH=CHCHCl.