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Chemistry · 2026 · 5 marks
Aldehydes, Ketones and Carboxylic AcidsChemical Reactions of Aldehydes, Ketones and Carboxylic Acids5 marksApplylong answer
CBSE 2026 · Region 4 · Set 1 · Q32
(a) (i) How will you bring about the following conversions: (I) Bromobenzene to 1-phenylethanol (II) Benzene to m-nitroacetophenone (ii) An organic…
(i)
How will you bring about the following conversions :
(I)
Bromobenzene to $\displaystyle 1$-phenylethanol
(II)
Benzene to m-nitroacetophenone
(ii)
An organic compound with the molecular formula $\displaystyle \mathrm{C}_{8} \mathrm{H}_{8} \mathrm{O}$ forms $\displaystyle 2,4$-DNP derivative, reduces Tollens' reagent and undergoes Cannizzaro reaction. On vigorous oxidation with acidic or alkaline $\displaystyle \mathrm{KMnO}_{4}$ it gives Benzene-$\displaystyle 1,2$-dicarboxylic acid. Identify the compound and write the products when it undergoes Cannizzaro reaction.
(iii)
Arrange the following compounds in increasing order of their acid strength : $\displaystyle \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}, \mathrm{O}_{2} \mathrm{~N}-\mathrm{CH}_{2}-\mathrm{COOH}, \mathrm{CF}_{3}-\mathrm{COOH}, \mathrm{HCOOH}$
(i)
Write the products formed when benzaldehyde reacts with the following reagents :
(I)
$\displaystyle 2,4$-Dinitrophenylhydrazine
(II)
Acetophenone in the presence of dilute NaOH followed by heating
(ii)
Give reasons for the following :
(I)
Benzoic acid does not undergo Friedel-Crafts reaction.
(II)
Carboxylic acids have higher boiling point than alcohols of comparable molecular mass.
(iii)
Write simple chemical test to distinguish between propanal and propanone.
Marking-scheme solution
(i)
(I)
(II)
(ii)
(iii)
C6H5COOH < HCOOH < O2N-CH2-COOH < CF3-COOH
(i)
(I)
(II)
(ii)
(I)
Because of the formation of salt where carboxyl group is deactivating and gets
bonded with lewis acid (Anhydrous AlCl3).
(II)
Because of more extensive association of carboxylic acid molecules through
intermolecular hydrogen bonding./ Dimer formation takes place.
(iii)
On warming with freshly prepared ammoniacal solution of AgNO3 (Tollens’
reagent) propanal forms bright silver mirror whereas propanone does not.
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CBSE Class 12 Chemistry past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.