Chemistry MCQs for NEET — Practice Questions with Answers

The reagent $Hg^{2+} / H_2SO_4$ is used to convert alkynes to ketones. In this case, But-1-yne would be converted to Butane-2-one through a hydration reaction in the presence of mercury(II) sulfate as a catalyst. This reaction involves the addition of water (H-OH) across the triple bond, following Markovnikov's rule, resulting in the formation of a ketone.

$ CH \equiv CH \xrightarrow [] {HBr} CH_2 = CH - Br \xrightarrow [] { Hbr} CH_3-CHBr_2 $ Ethylidene bromide

$ CH \equiv CH \xrightarrow [] { HCN} CH_2 = CH - CN $

$ CH_3 -CH_2 - C \equiv CH \xrightarrow[] { KMnO4 / KOH } CH_3 CH_2 COOH + CO_2 + H_2 O $ (terminal alkyne) Oxidation of terminal alkyne gives acid and $ CO_2 $

$ CH_3 -C \equiv C - CH_3 \xrightarrow [KOH] { KMnO_4} CH_3COOH + CH_3COOH $ (nonterminal alkyne) Oxidation of nonterminal alkyne gives mixture of two acids

$ CH \equiv CH + CH_3CH_2 MgBr \rightarrow CH_3CH_3 + CH \equiv CMgBr $

According to Que-76

Reductive ozonolysis of But-2-yne gives Buta-2,3-dione. In reductive ozonolysis, the alkyne is cleaved by ozone (O3) and reduced to form diketones. Specifically, But-2-yne is broken down into two molecules of Buta-2,3-dione as the carbon-carbon triple bond is split and each carbon forms a double bond with oxygen.

The reduction of alkynes to trans-alkenes can be achieved using sodium or lithium in liquid ammonia. This is known as the Birch reduction. For 2-hexyne, using $ Li / NH_3 $ will yield trans-2-hexene.