CBSE 2024 · Region 2 · Set 1 · Q32 · 5 marks
(i)Account for the following :(1)Oxidation of aldehydes is easier as compared to ketones.(2)The alpha ( $\displaystyle \alpha$ ) hydrogen atoms of aldehydes are acidic in nature.(ii)Write the products in the following reactions :(1)
(2)
(iii)Give a simple chemical test to distinguish between ethanoic acid and ethanal. \[\](i)Draw structure of the $\displaystyle 2,4$-dinitrophenylhydrazone of benzaldehyde.(ii)Arrange the following in increasing order of their reactivity towards HCN : $\displaystyle \mathrm{CH}_{3} \mathrm{COCH}_{3},\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}-\mathrm{COCH}_{3}, \mathrm{CH}_{3} \mathrm{CHO}$(iii)How can you convert phenyl magnesium bromide to benzoic acid ?(iv)Give a simple chemical test to distinguish between benzaldehyde and ethanal.(v)Write the main product in the following reaction :
(i)
Account for the following :
(1)
Oxidation of aldehydes is easier as compared to ketones.
(2)
The alpha ( $\displaystyle \alpha$ ) hydrogen atoms of aldehydes are acidic in nature.
(ii)
Write the products in the following reactions :
(1)
(2)
(iii)
Give a simple chemical test to distinguish between ethanoic acid and ethanal. \[\]
(i)
Draw structure of the $\displaystyle 2,4$-dinitrophenylhydrazone of benzaldehyde.
(ii)
Arrange the following in increasing order of their reactivity towards HCN : $\displaystyle \mathrm{CH}_{3} \mathrm{COCH}_{3},\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}-\mathrm{COCH}_{3}, \mathrm{CH}_{3} \mathrm{CHO}$
(iii)
How can you convert phenyl magnesium bromide to benzoic acid ?
(iv)
Give a simple chemical test to distinguish between benzaldehyde and ethanal.
(v)
Write the main product in the following reaction :
Marking-scheme solution
(i)
($\displaystyle 1$)Because oxidation of aldehyde involves cleavage of C - H bond which is weaker than C - C bond of ketone.
(2)
Electron withdrawing nature of carbonyl group/ Due to resonance stabilization of the conjugate base.
(ii)
<smiles>CCCCCCCC(=O)c1ccccc1</smiles>
(2)
(iii)
On heating with \(\displaystyle \mathrm{NaOH}+\mathrm{I}_{2}\), ethanal gives yellow ppt.Of \(\displaystyle \mathrm{CHI}_{3}\) whereas ethanoic acid does not.
Aldehydes, Ketones and Carboxylic AcidsChemical Reactions of Aldehydes, Ketones and Carboxylic AcidsApplylong_answermedium
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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.