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CSS past paper

CSS Chemistry Paper II Past Paper 2021

CSS Chemistry Paper II 2021 carries 100 marks over 3 hours. It has 7 questions.

Marks
100
Time
3 hours
Questions
7

Years

How to attempt: Attempt ONLY FOUR questions from PART-II. ALL questions carry EQUAL marks.

Questions

Question 1 (Part I) is the paper's MCQs, which are not reproduced here.

  1. Q. 2
    (20)
    • (a)
      Describe factors that influence keto-enol tautomerization. Elaborate the statement with the help of examples.
      (10)
    • (b)
      Assign “R” or “S” configuration on each of the chiral centers of the given compounds.
      (10)
      Three structures: a cyclohexane with a hashed OH and a wedged Cl on adjacent carbons; a two-carbon fragment with HO and a wedged Br on the upper carbon and H2N (hashed bond) and CH3 on the lower carbon; a cyclohexane bearing CH3 (wedge, top), OH (hashed), CH3 (hashed), Cl (hashed, bottom), H2N (wedge) and Br (hashed) around the ring.
  2. Q. 3
    (20)
    • (a)
      Give the products expected (if any) when ethylbenzene reacts under following conditions: (02 marks each)
      (10)
      • (i)
        BrX2\ce{Br2} in CClX4\ce{CCl4} (dark)
      • (ii)
        HNOX3\ce{HNO3},HX2SOX4\ce{H2SO4}
      • (iii)
        Conc. HX2SOX4\ce{H2SO4}
      • (iv)
        Propanoyl chloride drawn skeletally: C2H5 attached to a carbon bearing a double-bonded O and Cl.

        , AlClX3\ce{AlCl3}(1.1 equiv.), then HX2O\ce{H2O}

      • (v)
        Alkaline KMnOX4\ce{KMnO4}
    • (b)
      Account for the following: (05 marks each)
      (10)
      • (i)
        Intramolecular H-bonding is stronger than intermolecular H-bonding
      • (ii)
        Control of nucleophilic substitution reaction over elimination reactions
  3. Q. 4
    (20)
    • (a)
      Write down reagents, reaction conditions and important steps for the following conversions:
      (10)
      • (i)
        Chlorobenzene to 2,4-dinitrophenyl hydrazine
      • (ii)
        Pyridine to 2-amino pyridine
    • (b)
      Write a note that substituents on aromatic rings dictate reactivity and orientation of the incoming electrophile in electrophilic aromatic substitution reactions.
      (10)
  4. Q. 5
    Draw detailed mechanisms for: (04 marks each)
    (20)
    • (i)
      Succinaldehyde (OHC-CH2CH2-CHO, skeletal) + acetone (skeletal) with CH3NH2 over the arrow, giving tropinone (a bicyclic amine with an N-CH3 bridge and a ring ketone).
    • (ii)
      Acetic anhydride (skeletal) + benzaldehyde (benzene ring with CHO) with sodium acetate (CH3COO⁻ Na⁺) over the arrow, giving cinnamic acid (benzene ring-CH=CH-COOH).
    • (iii)
      A benzene ring with CHO and, ortho to it, NHTs; over the arrow NaH, Et2O and CH2=CHPPh3, under it DMF, Reflux, 48h; giving a 1,2-dihydroquinoline with Ts on the nitrogen.
    • (iv)
      2-Methylcyclohexanecarboxylic acid (skeletal, COOH on the ring next to a methyl) with i- SOCl2, CH2N2 and ii- AgO, CH3OH over the arrow, giving methyl (2-methylcyclohexyl)acetate (ring with CH3 and CH2C(=O)OCH3).
    • (v)
      Cyclohexanone with i- NH2OH and ii- H2SO4 over the arrow, giving caprolactam (a seven-membered ring containing C=O and NH).
  5. Q. 6
    Account for the following: (05 marks each)
    (20)
    • (i)
      In DNA, a guanine residue reacts with electrophiles predominantly at the 7 and 3 positions of the ring system (see below). Suggest an explanation for this.
      Guanine (a fused six- and five-membered ring system with C=O, HN, H2N and NH groups) with dashed arrows labelled 7-position pointing to N7 of the five-membered ring and 3-position pointing to N3 of the six-membered ring.
    • (ii)
      Outline the synthesis of following compound:
      An α,β-unsaturated aldehyde (CH=O at one end) whose alkene carbon bears a p-tolyl group and whose other alkene carbon is attached through CH2 to a second p-tolyl group (skeletal; 2,4-di-p-tolylbut-2-enal).
    • (iii)
      A Grignard reagent that is a key intermediate in an industrial synthesis of vitamin A can be synthesized in the following way:
      HC≡CLi + methyl vinyl ketone (skeletal) with 1. Liq. NH3, 2. NH4+ over and under the arrow gives A (C6H8O); A with H3O+ gives B, HO-CH2-CH=C(CH3)-C≡CH (skeletal); B with 2C2H5MgBr gives C (C6H6Mg2Br2O).

      What are the structures of compounds A and C? The acid catalysed rearrangement of A to B takes p1.

    • (iv)
      What are compounds A and B in the reaction given below? Compound B has a strong IR absorption band in the 1650–1730 cm−1^{-1} region and a broad strong band in the 3200–3550 cm−1^{-1} region.
      1-Methylcyclohexene→2 ⋅ NaHSOX31 ⋅ OsOX4A (CX7HX14OX2)→CHX3COX2HCrOX3B (CX7HX12OX2)\text{1-Methylcyclohexene} \ce{->[1. OsO4][2. NaHSO3]} \textbf{A}\ (\ce{C7H14O2}) \ce{->[CrO3][CH3CO2H]} \textbf{B}\ (\ce{C7H12O2})
  6. Q. 7
    Explain the following: (04 marks each)
    (20)
    • (i)
      How can IR be used to help interpret NMR spectra?
    • (ii)
      What are diastereotopic protons? Explain with examples.
    • (iii)
      Determine the structure for a compound with formula CX6HX4NX2OX4\ce{C6H4N2O4} with following 1^{1}H-NMR data:

      δ 8.76 t (1H), 8.38 dd (2H), 7.97 t (1H)

    • (iv)
      Assign chemical shifts of each proton in the above structure.
    • (v)
      Why 13^{13}C-NMR is less sensitive than 1^{1}H-NMR?
  7. Q. 8
    Answer following questions: (04 marks each)
    (20)
    • (i)
      Comment if glycogenesis is anabolic or catabolic. Write down all steps involve in glycogenesis.
    • (ii)
      Describe endergonic and exergonic reactions
    • (iii)
      Write a note on anionic and cationic surfactants.
    • (iv)
      Comment if waste glass can be used for cement production.
    • (v)
      What is the chemical composition of nucleic acids and their biological significance?
  1. Part-II is to be attempted on the separate Answer Book.
  2. Attempt ONLY FOUR questions from PART-II. ALL questions carry EQUAL marks.
  3. All the parts (if any) of each Question must be attempted at one place instead of at different places.
  4. Candidate must write Q. No. in the Answer Book in accordance with Q. No. in the Q.Paper.
  5. No Page/Space be left blank between the answers. All the blank pages of Answer Book must be crossed.
  6. Extra attempt of any question or any part of the attempted question will not be considered.