Skip to content

Answer the following… (Class 12 Chemistry 2026, Q31b)

questionbuddy.in/q/cbse-12-chemistry-2026-56-1-1-q31b-draw-structure-dinitrophenyl-hydrazone-derivative

ChemistryCBSE Class 12 · Board exam 2026, set 56/1/1 · 5 marks · Long answer

CBSE Class 12 Chemistry 2026: question 31(b)

Set in the CBSE Class 12 board exam of 2026, paper 56/1/1, section E, question 31(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q31(b) · 5 marks · Long answerAldehydes, Ketones and Carboxylic Acids

Answer the following questions :
(i) Draw structure of the 2, 4-dinitrophenyl hydrazone derivative of benzaldehyde.
(ii) Arrange the following in increasing order of their reactivity towards HCN :
Di-tert. butyl ketone, Acetaldehyde, Acetone
(iii) Give a simple chemical test to distinguish between benzoic acid and ethyl benzoate.
(iv) Write the name of the reagent to convert Ethanenitrile to Ethanal.
(v) Draw the structure of 'X' in the following reaction :
cyclohexanol 'X'

Figure in the paper: Part (v) shows a cyclohexane ring bearing an –OH group, with arrow labelled CrO3 leading to 'X'. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 56/1/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

2,4-DNP condenses with C=O to form C=N–NH–Ar.

Hint 2

Bulky alkyl groups hinder nucleophilic attack on C=O.

Hint 3

A secondary alcohol is oxidised to a ketone; only an acid reacts with bicarbonate.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (i) The 2,4-DNP derivative of benzaldehyde is . The benzene ring on NH carries –NO₂ groups at positions 2 and 4.

    1 mark

  2. (ii) Reactivity towards HCN falls as steric hindrance and the +I effect at the carbonyl carbon increase:
    Di-tert-butyl ketone < Acetone < Acetaldehyde

    1 mark

  3. (iii) Add solution to each. Benzoic acid gives brisk effervescence of ; ethyl benzoate gives none.

    1 mark

  4. (iv) The reagent is DIBAL-H (diisobutylaluminium hydride) followed by . Alternatively, use followed by (Stephen reduction).

    1 mark

  5. (v) oxidises the secondary alcohol to a ketone. X = cyclohexanone, a six-membered ring with a C=O group.

    1 mark

Answer: (i) C₆H₅CH=N–NH–C₆H₃(NO₂)₂-2,4; (ii) Di-tert-butyl ketone < Acetone < Acetaldehyde; (iii) NaHCO₃ test (effervescence with benzoic acid); (iv) DIBAL-H then H₂O (or SnCl₂/HCl, H₃O⁺); (v) X = cyclohexanone

Where the marks are

  • Correct 2,4-DNP derivative structure (1 mark)
  • Correct increasing order (1 mark)
  • NaHCO₃ test with observations (1 mark)
  • DIBAL-H/H₂O or SnCl₂–HCl/H₃O⁺ (1 mark)
  • Cyclohexanone (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Aldehydes, Ketones and Carboxylic Acids, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 56/1/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.