Question

$\text{Ethynylbenzene}\stackrel{H{g}^{2+}/H^{+}}{\to }\text{Product}$

What is the major product of the following reaction?

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

Like alkanes and alkenes, alkynes are also immiscible in water and do not react with water. However when one molecule of water adds to an alkyne is warmed with $HgS{O}_4$ and dil. $H_{2}S{O}_4$ at 333 K it forms a carbonyl compound.
The addition of $H_{2}O$ to the alkynes follows Markovnikov's rule. This gives the major product.
Markovnikov's rule : Negative part of the addendum (adding molecule) gets attached to that doubly bonded C which posses lesser number of hydrogen atoms.
Here, the enol form formed after tha addition of $H_{2}O$ shows Keto-enol tatutomerism to give stable keto form.


Hence, the major product of the given reaction is compound (B)