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KCET 2021 Chemistry Solved Paper

Question : 6 of 60

Marks: +1, -0

A, B and C respectively are

Solution:

Ethyne on reaction with

\mathrm{HgSO}_4 / \mathrm{H}_2\mathrm{SO}_4

gives ethanol (i.e.

\mathrm{CH}_2=\mathrm{CH}-\mathrm{OH}

) which interconvert (i.e. tautomerises) to give acetaldehyde

(\mathrm{CH}_3\mathrm{CHO})

\mathrm{CH}\equiv\mathrm{CH}\xrightarrow[\mathrm{H}_2\mathrm{SO}_4]{\mathrm{HgSO}_4}\mathrm{CH}_2=\mathrm{CH}-\mathrm{OH}\overset{\text{Tautomeriscs}}{\rightleftharpoons}\mathrm{CH}_3\mathrm{CHO}

PCC is an oxidising agent, which oxidised the alcohol to aldehyde. Therefore,

(B)

is an alcohol, i.e. ethanol.

\mathrm{CH}_3\mathrm{CH}_2\mathrm{OH}\xrightarrow{\text{PCC}}\mathrm{CH}_3\mathrm{CHO}

Ethane nitrile on reaction with

\mathrm{SnCl}_2 / \mathrm{HCl}

followed by acid hydrolysis give acetaldehyde.

\mathrm{CH}_3\mathrm{CN}\xrightarrow[(ii)\,\mathrm{H}_3\mathrm{O}^+]{(i)\,\mathrm{SnCl}_2/\mathrm{HCl}}\mathrm{CH}_3\mathrm{CHO}

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