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The reaction of cyclooctyne with HgSO4 in the presence of aqueous H2SO4gives,
A.
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B.
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C.
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D.
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Answer
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Hint: -The reaction of alkyne and HgSO4 in the presence of aqueous H2SO4 gives carbonyl compounds ,it may be aldehyde or may be ketone .This reaction is also known as Kucherov reaction.
Now. Let’s discuss the general Kucherov reaction which is shown below.

Complete step by step solution
Due to the presence of two pi-bonds, alkynes have a very low tendency for electrophilic addition than alkenes. But with the help of various promoter catalysts such as HgSO4 and CdSO4 electrophilic addition can take place.
Let us see the mechanism for the general reaction of alkyne with HgSO4 in the presence of aqueous H2SO4 ;
In the first step, protonation of alkyne will take place by the HgSO4 and nucleophile H20 which will react with the pi-bond of the alkyne. After the attack both removal of hydrogen ions will take place and there will be removal of HgSO4 using acidic work up. Then enol will be formed. Then these enols get tautomerized to ketone which is the desired product.
Keto-enol tautomerism is a very famous and they interconverted using acid or base. Normally keto form compounds are more stable than the enol form compound. But there are few examples where keto form is also very stable.
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Similarly, when cyclooctyne reacts then there will be a formation of enol which gets ketomerises to keto form as keto form is more stable.
The reaction that takes place is;
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Hence, option D is correct.

Note:

With the same mechanism, when alkenes are treated with the same reagents then there will be the formation of the corresponding alcohol.


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