When propyne reacts with hydrogen chloride, the product is 2-chloropropene. This reaction is an example of electrophilic addition, in which the hydrogen chloride molecule adds to the double bond of the propyne molecule. The hydrogen atom from the hydrogen chloride molecule adds to the carbon atom of the double bond that is bonded to the fewer hydrogen atoms, while the chlorine atom adds to the other carbon atom.

The reaction can be represented as follows:

```

CH3-C≡CH + HCl → CH3-CH=CHCl

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