UPSC Civil Services (Mains), Chemistry optional · 2021 · Paper II
Q8(b)(ii). Two UV bands of acetone
Question
The UV spectrum of acetone exhibits two signals of different intensities, one at λmax 280 nm and the other at λmax 190 nm. Assign the corresponding electronic transitions to the observed signals.
Answer in brief
280 nm (weak, ε ≈ 15) is the n → π* transition of C=O; 190 nm (strong, ε ≈ 1000) is the π → π* transition.
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CoversUV spectroscopyn→π* transitionπ→π* transitionacetoneλmaxmolar absorptivity
All parts of Question 8
- 8(a)(i) Products X and Y in four reagent problems15 marks
- 8(a)(ii) 2-Methylbut-1-ene with diborane5 marks
- 8(b)(i) C₉H₁₈O with a single ¹H NMR line10 marks
- 8(b)(ii) Two UV bands of acetone5 marks
- 8(c)(i) ¹H NMR spectrum of methyl propenoate10 marks
- 8(c)(ii) Two carbonyl bands of chloroacetone5 marks