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Part II
Q. 3
(a)Using Zaitsev's rule, predict which would be the major product of the following reaction. Also justify your answer. [Structure shown: Cyclopentane with Br and CH3 groups] + EtONa/EtOH, 55°C → [Two possible products shown] [4]
(b)Give the equation for the following reactions along with reaction conditions: Reduction of propyl bromide Synthesis of acetone from propene Synthesis of cyclohexane from phenol Oxidation of ethylene in hot and cold KMnO₄ [8]
(c)A compound with molecular formula C₄H₈O has a strong IR absorption spectrum at 1730 cm⁻¹. Its mass spectrum is tabulated below, and includes key peaks at m/z 44 (the base peak) and m/z 29. Propose a structure for the compound and write fragmentation equations showing how peaks having these m/z values arise. Table: Mass spectrum of an unknown compound m/z Intensity (as percent of base peak) m/z Intensity (as percent of M⁺ ) 27 59.0 72 M⁺ 100.0 28 15.0 73 M⁺ +1 4.5 29 54.0 74 M⁺ +2 0.3 39 23.0 41 60.0 [Recalculated to base on M⁺ ] 42 12.0 43 79.0 44 100.0 (base) 72 73.0 M⁺ 73 3.3 74 0.2 [8]
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Q. 4
(a)Answer the following:
(b)with positive charge] Write the structures of two chair conformations of 1-tert-butyl-1-methylcyclohexane. Which conformation is more stable? Explain your answer. Why alkenes are more reactive than alkanes in chemical reactions. [10]
(c)Nucleophilic Centers Nucleophiles are electron-rich species seeking electrophilic sites:
(d)1-tert-butyl-1-methylcyclohexane Conformations The two chair conformations involve the bulky tert-butyl group occupying either an equatorial or axial position.
(e)Reactivity: Alkenes vs. Alkanes Alkenes are more reactive than alkanes because they possess a π bond . The π electrons are held less tightly than σ electrons and are located above and below the plane of the carbon atoms, making them easily accessible to electrophilic attack . Alkanes are saturated, stable sp3 hydrocarbons with strong σ bonds, requiring high activation energy for substitution reactions. ( b ) Consider the following pairs of structures. Designate each chirality center as (R) or (S) and identify the relationship between them by describing them as representing enantiomers, diastereomers, constitutional isomers, or two molecules of the same compound. H-C(CH3)(F)(Br) and H3C-C(H)(Br)(F) [Stereochemical structures shown with dashes and wedges] H-C(CH3)(Br)(H3C) and Br-C(CH3)(H)(F) with H3C-C(H)(F)(CH3) [Stereochemical structures shown with dashes and wedges] [5]
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(15)
Q. 5
(a)Give structures (including stereochemistry where appropriate) for compounds A-D: Benzene + C₆H₅-CO-Cl (with AlCl₃) → A (with PCl₅ at 0°C) → B (C₉H₁₀Cl₂) B (with 2 NaNH₂ in mineral oil, heat) → C (C₉H₈) C (with H₂, Ni/B (P-2)) → D (C₉H₁₀) [Hint: The ¹H NMR spectrum of compound C consists of a multiplet at δ 7.20 (3H) and a singlet at δ 2.0 (3H).] [5]
(b)Which diene and dienophile would you employ in the synthesis of following? Give mechanism also. [Structure shown: Benzene ring with methyl groups and two ester groups (OMe)] [5]
(c)Propose a structure for an alcohol with molecular formula C₅H₁₂O that has the ¹H NMR spectrum given in Figure below. Assign the chemical shifts and splitting patterns to specific aspects of the structure you propose. [¹H NMR spectrum shown with peaks at: - 6H (appears to be around δ 0.9) - 1H (appears to be around δ 1) - 2H (appears to be around δ 1) - 3H (appears to be around δ 1)] [5]
(d)What are the common by-products generated during sugar manufacturing process. Discuss the applicability of each by-product in perspective of Pakistan. [5]
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Q. 6
(a)Starting with styrene, outline a synthesis of 1-bromo-2-phenylethane. [Structure shown: Benzene-CH=CH₂ → C₆H₅-CH₂-CH₂-Br] [5]
(b)Urea cycle is illustrated in figure below. Explain the significance of the urea cycle in the context of nitrogen metabolism. How does the urea cycle prevent the toxic accumulation of ammonia in the body? [figure] [5]
(c)Illustrate the mechanism for dehydrating an alcohol to produce an alkene, using ethanol as a specific example. [5]
(d)What is the role of grinding and milling processes in cement manufacturing. How do they impact the fineness of the final product? [5]
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(20)
Q. 7
(a)Compare and contrast the Lucas test and the dichromate test for alcohols. Provide a detailed explanation of the procedures, observations involved, and the specific observations or results expected in each test. Highlight the distinguishing features that allow these tests to differentiate between primary, secondary, and tertiary alcohols. [5]
(b)Compare the structure of saturated and unsaturated fatty acids and explain their impact on human health. [5]
(c)Describe the process of glycolysis. Include the key intermediates, enzymes involved, and the fate of pyruvate under aerobic and anaerobic conditions. [5]
(d)Explain the role of limestone in cement production and its impact on the chemical composition of the final product. [5]
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Q. 8
(a)Competition experiments are those in which two reactants at the same concentration (or one reactant with two reactive sites) compete for a reagent. Predict the major product resulting from each of the following competition experiments: [Structure shown with two Cl groups on a chain] + I⁻ in DMF → [Product] [Structure shown with two Cl groups on a chain] + H₂O in acetone → [Product] [8]
(b)Define phospholipids and discuss their structural components. Explain how the structure of phospholipids contributes to their unique properties in biological membranes. Describe the process of phospholipid synthesis. [6]
(c)Explain the role of enzymes in biomolecular reactions, providing examples of specific enzymatic reactions. [6]
The 2024 CSS Chemistry paper set by the Federal Public Service Commission. Question wording only; questions marked “Not yet checked” have not been compared with the official paper yet. Open the official paper beside the questions to check any of them.
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