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Would you expect… (Class 12 Chemistry 2025, Q19)

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ChemistryCBSE Class 12 · Board exam 2025, set 56/1/1 · 2 marks · Very short answer

CBSE Class 12 Chemistry 2025: question 19

Set in the CBSE Class 12 board exam of 2025, paper 56/1/1, section B, question 19, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q19 · 2 marks · Very short answerAldehydes, Ketones and Carboxylic Acids

Would you expect benzaldehyde to be more reactive or less reactive in nucleophilic addition reactions than propanal ? Justify your answer.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 56/1/1.

Hints

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

Hint 1

Nucleophilic addition depends on how positive the carbonyl carbon is.

Hint 2

What effect does a benzene ring attached directly to C=O have through resonance?

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. Benzaldehyde is less reactive than propanal in nucleophilic addition reactions.

    1 mark

  2. In benzaldehyde the C=O group is conjugated with the benzene ring. Resonance releases electrons from the ring towards the carbonyl carbon and reduces the polarity of C=O. Its carbonyl carbon is therefore less electrophilic than that of propanal, so a nucleophile attacks it less easily.

    1 mark

Answer: Less reactive, because resonance with the benzene ring makes its carbonyl carbon less electrophilic

Where the marks are

  • States that benzaldehyde is less reactive (1 mark)
  • Resonance reduces the electrophilicity or polarity of the carbonyl carbon (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 paper2025 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.