Q10(c). Band width and colour; ν(C=O) of acids and ketones
Explain the following: (i) p-nitroaniline and anthracene both absorb near 375 nm but p-nitroaniline is yellow while anthracene is colourless. (ii) Monomeric saturated aliphatic carboxylic acids show carbonyl stretching frequency near 1760 cm⁻¹ while the saturated aliphatic ketones near 1720 cm⁻¹.
Model answer
The free solution for 2024 answers questions 1, 4, 5, 6, 7 and 9, the ones picked in its time plan. Question 10 is answered in full in the Geo-Scientist Chemistry Paper III, 2021 to 2025 book, with every part of every paper.
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UPSC Combined Geo-Scientist (Main) Chemistry Paper III: Model Answers 2021 to 2025
- All ten questions of each paper, with the question printed above its answer
- Instruments drawn as labelled diagrams, numericals worked with units
- Topic-wise weightage and a topic-wise index
CoversUV-visible spectroscopyband width and colourp-nitroanilineIR carbonyl stretchinginductive effectcarboxylic acid
All parts of Question 10
- 10(a)(i) Anisole with dibromocarbene: ring expansion to a tropone5 marks
- 10(a)(ii) Benzophenone with aluminium isopropoxide at 250 °C5 marks
- 10(b) Structure from ¹H and ¹³C NMR: C₁₅H₁₄O5 marks
- 10(c) Band width and colour; ν(C=O) of acids and ketones5 marks
- 10(d)(i) Mass spectral fragmentation of an ester and a cyclohexene5 marks
- 10(d)(ii) Structure from IR, ¹H and ¹³C NMR: C₁₀H₉NO₂5 marks