COMEDK 2025 Evening Solved Paper

Concept:Reductive ozonolysis cleaves each $C=C$ bond into two $C=O$ groups. If a vinylic carbon has no hydrogen (disubstituted), it forms a ketone; if it has one hydrogen, it forms an aldehyde.Explanation:Analyze each option based on the substitution at the double bond carbons.Option A: 1,2-butadiene ($\mathrm{CH}_2=C=CH-\mathrm{CH}_3$) gives a mixture including formaldehyde (from terminal $=CH_2$) and other aldehydes/ketones.Option B: 1,4-cyclohexadiene has each vinylic carbon as $CH$ (one H), so only aldehydes are produced.Option C: But-2-ene ($\mathrm{CH}_3-CH=CH-\mathrm{CH}_3$) has each vinylic carbon as $CH$ (one H), yielding two molecules of acetaldehyde (aldehyde).Option D: 2,3-dimethylbut-2-ene has the structure $(\mathrm{CH}_3)_2C=C(\mathrm{CH}_3)_2$. Each double-bond carbon is disubstituted (no H). Reductive ozonolysis gives only ketones:$$(\mathrm{CH}_3)_2C=C(\mathrm{CH}_3)_2 \xrightarrow{\mathrm{O_3/Zn}} 2\,\mathrm{CH_3COCH_3}$$Thus, only option D yields ketones exclusively.Answer:Option D