Question

What is the action of the following reagents on propyne?
(a) Chlorine gas
(b) hydrogen iodide

Answer 1

Propyne is an alkyne and it is an unsaturated hydrocarbon with the formula ${C_3}{H_4}$. In organic chemistry, a reagent is a compound or substance that is added to a system to cause a chemical reaction or to test if a chemical reaction occurs or not.

Complete answer: (a) When propyne reacts with an excess amount of chlorine gas, hydrochloric acid is formed. Alkynes undergo a halogenation reaction when they react with halogens. The chemical reaction between propyne and chlorine gas takes place in the following way:

(b) When alkynes react with hydrogen halides, trans-vinyl halides are formed. If the reaction takes place in the presence of excess hydrogen halide, then geminal dihalide is formed. This reaction is an example of electrophilic addition and the major product is determined from the markovnikov’s rule. When an alkyne is treated with one equivalent of hydrogen halide, vinyl halides are formed. When propyne reacts with hydrogen iodide, $2 - {\text{iodopropene}}$ is formed. The chemical reaction between propyne and hydrogen iodide takes place in the following way:

Note:
When alkynes react with hydrogen halides, the major product is predicted by using the Markovnikov’s rule i.e the hydrogen gets attached to the carbon which already has the most number of hydrogen atoms attached to it. This reaction proceeds via a termolecular mechanism. The reaction which involves the simultaneous collision of three ions, atoms or molecules is called a termolecular reaction.