UPSC Civil Services (Mains), Chemistry optional · 2023 · Paper II

Q6(c)(ii). Order of chemical shift of the lettered protons

10 marks
Topic: Spectroscopy
Question only

Question

Assign and arrange the lettered protons (Ha, Hb, Hc, (CH₃)d, He) in the increasing order of their chemical shift value in the ¹H NMR spectrum. [structure given in the paper]

Model answer

The free solution for 2023 answers questions 1, 2, 3, 5 and 8, the ones picked in its time plan. Question 6 is answered in full in the Chemistry Paper II, 2021 to 2025 book, with every part of every paper.

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UPSC Civil Services (Main) Chemistry Paper II: Model Answers 2021 to 2025

All eight questions of each paper, with the question printed above its answer
Mechanisms drawn out and labelled on the scheme
Topic-wise weightage and a topic-wise index

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Topic notes: ¹H and ¹³C NMR: chemical shift, spin–spin coupling and coupling constants, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverschemical shift¹H NMRdeshieldingaldehyde protonvinylic proton

All parts of Question 6

6(a)(i) Energy change of HCl + D₂ → DCl + HD10 marks
6(a)(ii) C=O bands of butyric acid, its ethyl ester and its anhydride5 marks
6(b)(i) Products A, B and C10 marks
6(b)(ii) Tacticity: isotactic, syndiotactic and atactic polymers5 marks
6(c)(i) Structure of C₁₆H₂₅NO from IR and ¹H NMR10 marks
6(c)(ii) Order of chemical shift of the lettered protons10 marks