UPSC Chemistry 2022 — Paper II

(a) Ionization of 3,4-dichloro-1,2,3,4-tetramethylcyclobutene in SbF₅-SO₂ at –75 °C produces a reaction intermediate of its own kind. Predict the intermediate and comment on its stability and aromaticity. (10 marks) (b) Predict the structures of X and Y, and also mention the major product: (10 marks) (c) Out of the following list of reactants along with the reagents, identify the reaction which is not a condensation reaction. Propose a suitable mechanism for the products formed in this reaction: (10 marks) (i) Acetaldehyde is reacted with dilute KOH (ii) Benzaldehyde is reacted with acetic anhydride in presence of sodium acetate (iii) Benzaldehyde is reacted with malonic ester in presence of a base (iv) Benzaldehyde is reacted with concentrated KOH (d) Write down the structure(s) of the product(s) obtained in the following reactions. Provide suitable justification and propose the mechanisms: (10 marks) (i) [reaction diagram not shown] (ii) [reaction diagram not shown] (e) Predict the product(s) formed on heating the cyclopentadiene and provide a suitable justification to your answer. (10 marks)

(a) Predict the products X and Y in the following reactions: (5×3=15 marks) (i) [compound] →(1) O₃ (2) H₂O₂→ X + Y (ii) [compound] →PBr₃→ [intermediate] →Br₂ (57%)→ X (iii) CH₃—CH(CH₃)—CH₃ →Br₂/hv, 127 °C→ X + Y (b) (i) What happens when the compound A is heated with one equivalent of HI? Give the structure of the product. Justify your answer: (5 marks) A [structure not shown] (ii) Predict [A] and [B] in the following reaction: (5 marks) [Starting compound] →NBS, CCl₄→ [A] →NaOEt, EtOH/Δ→ [B] (iii) Give the structures of alkenes expected after dehydrohalogenation of 2-chloro-2,3-dimethylpentane by sodium ethoxide. (5 marks) (c) (i) Match the following for the synthesis of class of compounds listed in Set-I with the reactants and reagents of Set-II: (10 marks) Set-I: (A) Quinoline, (B) Isoquinoline, (C) Indole Set-II: (1) Cinnamaldehyde, hydroxylamine, P₂O₅; (2) Acetaldehyde, phenylhydrazine, acid; (3) Glycerol, aniline, acid, nitrobenzene; (4) α-Halocarbonyl compound, thiourea Propose the mechanism for the synthesis of indole. (ii) Write the reaction sequence for the synthesis of L-dopa (B), a drug for the treatment of Parkinson's disease, from L-tyrosine (A), an α-amino acid: (10 marks)

The compound A, acetal of acetaldehyde, on reaction with B, under given reaction conditions, yields C and the final product D : (i) Write down the structures of the products C and D. Propose a mechanism with suitable explanation. (ii) Write down the product(s) if ortho-ester E is used instead of the compound A under the similar reaction conditions :

(a) (i) Complete the following reaction by showing stepwise reaction mechanism for the formation of products : (ii) The compound A is optically active and upon treating A with alcoholic sodium ethoxide, it looses its optical activity. Justify : (b) (i) If more than one equivalent of Br₂ at high temperature are allowed to react with cyclopentane, how many dibromocyclopentanes would you expect as products? Draw their structures and name them. (ii) How will you convert p-nitrotoluene to m-nitrotoluene? (c) By using appropriate reagents and conditions, how will you convert phenol into coumarin? Give suitable mechanism for this transformation.

(a) Write the structures of nucleosides and nucleotides, and discuss the primary structures of DNA and RNA. (10 marks) (b) Write down the products obtained after photolysis of 2-methylcyclohexanone in solution phase. Explain the formation of products. (10 marks) (c) (i) By using appropriate reactants, reagents and conditions and using acetylene as starting material, how will you synthesize the following compound? (ii) Identify the products W, X, Y and Z in the following reactions: (10 marks) (d) (i) How will you distinguish between NH stretching absorption of a primary amine and a secondary amine by using IR spectroscopy? (ii) How will you distinguish among primary, secondary and tertiary alcohols on the basis of PMR spectroscopy? (8 marks) (e) Given below are the IR and NMR spectral characteristics of three compounds: (i) IR : 1750 cm⁻¹; NMR : δ 2·0 (s, 3H), 5·1 (s, 2H) and 7·3 (s, 5H) (ii) IR : 1740 cm⁻¹; NMR : δ 3·5 (s, 3H), 3·6 (s, 2H) and 7·4 (s, 5H) (iii) IR : 3200–2800 (various bands) and 1700 cm⁻¹; NMR : δ 2·75 (t, 2H), 2·95 (t, 2H), 7·4 (s, 5H) and 12·0 (s, 1H) Match each of these spectral data with one of the following structures: (1), (2), (3), (4), (5) (10 marks)

(a) (i) Predict the products in the following reactions: Propose suitable mechanism to justify your answer. (ii) Giving justification, write the major and minor product(s). Comment upon the chirality of recovered reactant (if any). (5+10=15 marks) (b) (i) How will you synthesize polypropylene (PP) by using Ziegler-Natta catalysis? Discuss the mechanism and its advantages over conventional polymerization. (10 marks) (ii) How is Perlon synthesized from ε-Caprolactam? Give the mechanism of the reaction. (5 marks) (c) (i) Write the structures of the products X, Y and Z in the following reactions and indicate the mechanism for the formation of X: (1) OsO₄, Pyridine (2) H⁺, H₂O; X →[HIO₄] Y + Z (10 marks) (ii) Write the major and minor products in the following reaction. Discuss the stereochemistry along with reaction mechanism for the formation of the major product: Ph-C(=O)-CH₃ →[m-CPBA] ? + ? (Major product + Minor product) (10 marks)

(a) Discuss the different types of secondary structures of proteins and compare these structures with tertiary structure of proteins. 15 marks (b) Complete the following reactions and give suitable mechanisms for the formation of products: (i) CH₃—CH₂—CH₂—C(=O)—Cl (1) 2NaBH₄ → ? (2) H₃O⁺ (ii) CH₃—C≡C—CH₃ Na in liq. NH₃ → ? 10+5=15 marks (c) (i) A compound (A) containing C, H and O has molecular weight 102 and displays two signals in the ¹H NMR spectrum at δ 1·1 (d) and 3·55 (septet) in the integral ratio of 6:1. Treatment of A with 1 mole of HI gives rise to B and C. In the IR spectrum, B gives a strong absorption band at 3330 cm⁻¹, whereas its ¹H NMR spectrum shows signals at δ 1·05(d, 6H), 3·6 (septet, 1H) and 4·4 (s, 1H, disappeared with D₂O). The ¹H NMR spectrum of C gives signals at δ 1·9(d, 6H) and 4·25 (septet, 1H). Reaction of A with excess of HI gives only C. Identify A, B and C. Write all the reactions involved. 10 marks (ii) Three isomeric compounds having MF C₅H₁₀O give positive 2,4-DNP test and display the following NMR spectral characteristics. Identify the compounds. Among them, one isomeric compound on treatment with KOH (concentrated) gives two products. Write their structures also: (1) A triplet at δ1.05 and a quartet at δ2.47 (2) Two singlets (3) A doublet at δ1.0, a singlet at δ2.1 and a septet at δ2.2 10 marks

(a) (i) Among the following compounds I and II, which has more carbonyl stretching frequency in IR spectra? Explain: I II 5 marks (ii) Complete the following reaction. Write the structures of A, B and C, and explain how IR spectroscopy is helpful to distinguish among them: H₃C OH CH₃ H⁺ A + B + C 10 marks (b) (i) Calculate the λ_max values of the following compounds: (1) (2) 10 marks (ii) Explain why 1,3-butadiene exhibits a lower λ_max for π → π* transitions compared to that of 1,3,5-hexatriene. 5 marks (c) (i) What is McLafferty rearrangement? Discuss the mass spectral fragmentation of butyl butyrate with the following given data of ions: m/z 101, m/z 73, m/z 71 and m/z 56 Write the structures of fragment ions. 10 marks (ii) (1) A compound with MF C₂H₂BrCl exhibits two doublets (J = 16 Hz) in its PMR spectrum. Suggest a suitable structure along with other possible structures. (2) How can the structures of A and B be decided based on their UV spectral data? [ λ_max = 296 nm (ε_max = 10700) and λ_max = 281 nm (ε_max = 20800) ] 10 marks