CBSE 2024 · Region 3 · Set 1 · Q32 · 5 marks
(i)Write the major product(s) in the following reactions :
(2)
(3)
(ii)Give simple chemical tests to distinguish between the following pairs of compounds :(1)and(2)Pentanal and Pentan-$\displaystyle 3$-one(i)Give reasons for the following :(1)In semicarbazide, only one $\displaystyle -\mathrm{NH}_{2}$ group is involved in the formation of semicarbazone.(2)Acetaldehyde is more reactive than acetone towards addition of HCN.(ii)(1)Arrange the following in decreasing order of their acidic strength : $\displaystyle \mathrm{CH}_{3} \mathrm{COOH}, \quad \mathrm{O}_{2} \mathrm{~N}-\mathrm{CH}_{2}-\mathrm{COOH}, \quad \mathrm{HCOOH}$(2)Name the reagent in the following reaction : \[\begin{aligned} \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}- & \mathrm{CH}_{2}-\mathrm{CN} \xrightarrow{?} \\ & \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{CHO} \end{aligned} \](iii)Write the reaction involved in Hell-Volhard-Zelinsky reaction.
(i)
Write the major product(s) in the following reactions :
(2)
(3)
(ii)
Give simple chemical tests to distinguish between the following pairs of compounds :
(1)
and
(2)
Pentanal and Pentan-$\displaystyle 3$-one
(i)
Give reasons for the following :
(1)
In semicarbazide, only one $\displaystyle -\mathrm{NH}_{2}$ group is involved in the formation of semicarbazone.
(2)
Acetaldehyde is more reactive than acetone towards addition of HCN.
(ii)(1)
Arrange the following in decreasing order of their acidic strength : $\displaystyle \mathrm{CH}_{3} \mathrm{COOH}, \quad \mathrm{O}_{2} \mathrm{~N}-\mathrm{CH}_{2}-\mathrm{COOH}, \quad \mathrm{HCOOH}$
(2)
Name the reagent in the following reaction : \[\begin{aligned} \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}- & \mathrm{CH}_{2}-\mathrm{CN} \xrightarrow{?} \\ & \mathrm{CH}_{3}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{CHO} \end{aligned} \]
(iii)
Write the reaction involved in Hell-Volhard-Zelinsky reaction.
Marking-scheme solution
(i)
(1)
Because one - \(\displaystyle \mathrm{NH}_{2}\) group adjacent to carbonyl group is involved in resonance with it .
(2)
Steric and electronic reasons / In acetone two alkyl groups reduce the electrophilicity of the carbonyl carbon more effectively than in acetaldehyde.
(ii) ($\displaystyle 1$) \(\displaystyle \mathrm{O}_{2} \mathrm{~N}-\mathrm{CH}_{2} \mathrm{COOH}>\mathrm{HCOOH}>\mathrm{CH}_{3} \mathrm{COOH}\)
(2) DIBAL H / H2O
(iii)
\(\displaystyle \mathrm{X}=\mathrm{Cl}, \mathrm{Br}\)
Aldehydes, Ketones and Carboxylic AcidsChemical Reactions of Aldehydes, Ketones and Carboxylic AcidsApplylong_answerhard
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CBSE Class 12 Chemistry past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.