What will be the major product when m-cresol is reacted with propargyl bromide (HC ≡ C - CH$$_2$$Br) in presence of K$$_2$$CO$$_3$$ in acetone?

Williamson Ether Synthesis

This reaction follows the mechanism of a classic Williamson Ether Synthesis, which proceeds via an $$\text{S}_\text{N}2$$ nucleophilic substitution pathway:

1. Deprotonation: Potassium carbonate ($$\text{K}_2\text{CO}_3$$) acts as a mild base. It selectively removes the acidic phenolic proton ($$-\text{OH}$$) from m-cresol to generate a highly nucleophilic m-cresolate (phenoxide) anion.
2. Nucleophilic Attack: The phenoxide oxygen atom attacks the electrophilic $$\text{sp}^3$$ carbon attached to the bromine atom in propargyl bromide ($$\text{HC}\equiv\text{C--CH}_2\text{Br}$$).
3. Leaving Group Departure: The bromide ion ($$\text{Br}^-$$) leaves simultaneously, forming a new carbon-oxygen ($$\text{C--O}$$) ether linkage.

Detailed Evaluation of Each Option:

• Option A: Electrophilic Ring Substitution Products

  This statement is incorrect. Under these conditions, the base deprotonates the oxygen atom, making it the most nucleophilic site. Ring alkylation (Friedel-Crafts style) does not compete with the rapid $$\text{S}_\text{N}2$$ displacement on oxygen.




• Option B (Correct Matrix): Propargyl m-Tolyl Ether

  This statement is correct. The nucleophilic phenoxide ion directly bonds with the propargyl group ($$-\text{CH}_2\text{--C}\equiv\text{CH}$$), giving an ether product where the intact m-cresol ring skeleton is preserved with a newly appended propargyloxy side chain: $$\text{CH}_3\text{--C}_6\text{H}_4\text{--O--CH}_2\text{--C}\equiv\text{CH}$$.




• Option C & D: Elimination or Alkyne Addition Products

  These statements are incorrect. Mild bases like $$\text{K}_2\text{CO}_3$$ in acetone do not cause elimination reactions on terminal propargyl halides, nor is there any active reagent or catalyst present to add across the triple bond ($$\text{C}\equiv\text{C}$$).

Conclusion:

The reaction cleanly transforms the phenolic group into an ether linkage through an $$\text{S}_\text{N}2$$ substitution without altering the aromatic ring or the terminal alkyne structure.

Answer: Option B — Propargyl m-tolyl ether