Chemistry 2022 Paper II 50 marks Explain

Q6

(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)

हिंदी में प्रश्न पढ़ें

(a) (i) निम्नलिखित अभिक्रियाओं में उत्पादों का अनुमान लगाइए: अपने उत्तर का औचित्य सिद्ध करने के लिए उपयुक्त क्रियाविधि प्रस्तावित कीजिए। (ii) औचित्य प्रदान करते हुए मुख्य तथा अल्प उत्पाद/उत्पादों को लिखिए। पुनःप्राप्त अभिक्रियक (अगर कोई है) की काइलतता पर टिप्पणी कीजिए। (5+10=15 अंक) (b) (i) ज़िग्लर-नाट्टा उत्प्रेरण के प्रयोग से आप पॉलीप्रोपिलीन (PP) का संश्लेषण कैसे करेंगे? क्रियाविधि बताइए तथा पारंपरिक बहुलकन (पॉलिमराइजेशन) की अपेक्षा फायदों की विवेचना कीजिए। (10 अंक) (ii) ε-कैप्रोलैक्टम से पर्लन को कैसे संश्लेषित करते हैं? अभिक्रिया की क्रियाविधि दीजिए। (5 अंक) (c) (i) निम्नलिखित अभिक्रियाओं में उत्पादों X, Y और Z की संरचना लिखिए तथा X के बनने की क्रियाविधि का उल्लेख कीजिए: (1) OsO₄, पिरिडीन (2) H⁺, H₂O; X →[HIO₄] Y + Z (10 अंक) (ii) निम्नलिखित अभिक्रिया में मुख्य तथा अन्य उत्पादों को लिखिए। मुख्य उत्पाद के बनने की विषम रसायन के साथ अभिक्रिया क्रियाविधि की विवेचना कीजिए: Ph-C(=O)-CH₃ →[m-CPBA] ? + ? (मुख्य उत्पाद + अन्य उत्पाद) (10 अंक)

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Directive word: Explain

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How this answer will be evaluated

Approach

Explain the reaction mechanisms and product formations across all four sub-parts, allocating approximately 30% time to (a)(i)-(ii) combined (15 marks), 30% to (b)(i)-(ii) combined (15 marks), and 40% to (c)(i)-(ii) combined (20 marks). Begin with clear product predictions and mechanisms for each transformation, using curved-arrow notation and stereochemical representations throughout. Conclude with comparative remarks on catalytic systems where relevant.

Key points expected

(a)(i) Correct prediction of products with detailed mechanistic pathway showing electron flow and intermediates
(a)(ii) Identification of major vs minor products with regio/stereochemical justification; analysis of chirality in recovered reactant
(b)(i) Ziegler-Natta synthesis of polypropylene: TiCl₄/AlEt₃ system, coordination-insertion mechanism, isotactic control, advantages over free-radical polymerization
(b)(ii) Perlon (Nylon-6) synthesis: ε-caprolactam ring-opening polymerization, acid/base-catalyzed mechanism with initiation and propagation steps
(c)(i) OsO₄ dihydroxylation product X, HIO₄ cleavage to carbonyl fragments Y and Z; syn-addition mechanism with cyclic osmate ester intermediate
(c)(ii) Baeyer-Villiger oxidation: regioselectivity based on migratory aptitude (Ph > CH₃), retention of configuration, stereochemical outcome with mechanism

Evaluation rubric

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	20%	10	Demonstrates flawless understanding of periplanar requirements in eliminations, migratory aptitude in Baeyer-Villiger (Ph > 3° > 2° > 1° > CH₃), stereospecificity of OsO₄ syn-dihydroxylation, and isotactic vs syndiotactic polymer microstructures; correctly identifies that HIO₄ cleaves vicinal diols to carbonyls	Identifies most products correctly but confuses syn/anti addition stereochemistry, misorders migratory aptitude, or conflates Ziegler-Natta with metallocene catalysis; minor errors in polymer tacticity definitions	Fundamental misconceptions such as anti-addition for OsO₄, incorrect migratory group identification in Baeyer-Villiger, or describing free-radical mechanism for Ziegler-Natta polymerization
Mechanism / equation	25%	12.5	All four mechanisms (elimination/addition in a, coordination-insertion in b(i), anionic ring-opening in b(ii), cyclic osmate ester/HIO₄ cleavage in c(i), Criegee intermediate in c(ii)) drawn with precise curved arrows, correct intermediates, and stereochemical fidelity; includes transition state representations where stereochemistry is determined	Mechanisms generally correct but missing key intermediates (e.g., omitting metallacyclobutane or Criegee intermediate), incomplete arrow pushing, or lacking stereochemical detail in transition states	Missing mechanisms entirely, incorrect arrow directions, impossible intermediates, or complete confusion between reaction types (e.g., SN1 vs E1 vs carbene mechanisms)
Numerical accuracy	10%	5	Correct stoichiometric relationships in polymerization (monomer:initiator ratios), proper calculation of oxidation states in catalytic cycles, accurate mass balance in HIO₄ cleavage products; quantitative comparison of polymer yields/efficiencies where relevant	Minor arithmetic errors in stoichiometry or oxidation state assignments that don't fundamentally undermine the mechanistic logic	Major errors in balancing equations, incorrect oxidation state assignments for Ti in Ziegler-Natta system, or impossible stoichiometry in product distributions
Diagram / structure	25%	12.5	Clear, unambiguous structural drawings with wedge-dash stereochemistry for all chiral centers; proper representation of polymer repeat units, regiochemical outcomes (head-to-tail vs head-to-head), and cyclic intermediates (osmate ester, Criegee); IUPAC-acceptable abbreviations for phenyl groups	Structures generally correct but stereochemistry implied rather than explicit, ambiguous bond angles, or inconsistent use of skeletal vs condensed formulas; polymer structures missing end groups	Unreadable or chemically impossible structures, missing double bonds, incorrect connectivity, complete absence of stereochemical indicators where required, or confusion between reactant and product structures
Application context	20%	10	Explicitly connects Ziegler-Natta catalysis to Indian petrochemical industry (Reliance, IOCL polypropylene production), discusses biodegradable alternatives to Perlon, relates OsO₄ dihydroxylation to pharmaceutical synthesis (Indian API industry), and comments on green chemistry alternatives (catalytic OsO₄ with NMO, enzymatic Baeyer-Villiger)	Brief mention of industrial relevance without specific Indian context, or generic statements about polymer applications without connecting to national manufacturing capabilities	No application context provided, or irrelevant digressions into unrelated industrial processes; failure to recognize that isotactic PP discovery revolutionized plastics industry including Indian market

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