Chemistry 2023 Paper II 50 marks Solve

Q4

4.(a)(i) Complete the above reaction and write the steps involved in the reaction. (5 marks) 4.(a)(ii) Arrange the above alkenes in ascending order of their relative rate of bromination in methanol. (5 marks) 4.(a)(iii) Complete the above reactions and give suitable mechanism. (10 marks) 4.(b) Complete the above reaction and give suitable mechanism. (10 marks) 4.(c)(i) How many β-hydroxy carbonyl compounds may be theoretically formed in the above reaction? Write the structure of the products formed. (10 marks) 4.(c)(ii) Write the synthesis of benzonitrile starting from benzene (Hint: may involve more than one step). (10 marks)

हिंदी में प्रश्न पढ़ें

4.(a)(i) निम्नलिखित अभिक्रिया को पूरा करें और इसमें शामिल चरणों को लिखें। (5 अंक) 4.(a)(ii) निम्नलिखित एल्कीनों की मेथनॉल में ब्रोमीनकरण की आपेक्षिक दर को आरोही क्रम में लिखें। (A) (B) (C) (D) (5 अंक) 4.(a)(iii) निम्नलिखित अभिक्रियाओं को पूरा करें और उपयुक्त क्रियाविधि दें: (10 अंक) 4.(b) निम्नलिखित अभिक्रिया को पूरा करें और उपयुक्त क्रियाविधि दें: (10 अंक) 4.(c)(i) निम्नलिखित अभिक्रिया में सैद्धांतिक रूप से कितने β-हाइड्रॉक्सी कार्बोनिल यौगिक बन सकते हैं? बनने वाले उत्पादों की संरचना लिखिए। (10 अंक) 4.(c)(ii) बेंजीन से बेंजोनाइट्राइल का संश्लेषण लिखिए। (संकेत: अभिक्रिया में एक से अधिक चरण हो सकते हैं) (10 अंक)

Evaluate your answer to this question → See all 2023 Chemistry questions

Directive word: Solve

This question asks you to solve. The directive word signals the depth of analysis expected, the structure of your answer, and the weight of evidence you must bring.

See our UPSC directive words guide for a full breakdown of how to respond to each command word.

How this answer will be evaluated

Approach

Solve each sub-part systematically, beginning with reaction completion and mechanism elucidation for 4(a)(i), (iii) and 4(b), followed by rate analysis for 4(a)(ii), stereochemical enumeration for 4(c)(i), and multi-step synthesis for 4(c)(ii). Structure the answer with clear sub-headings, balanced chemical equations with electron-pushing arrows, and concise structural diagrams.

Key points expected

Correct identification of reaction types: electrophilic addition, nucleophilic substitution, aldol condensation, and Sandmeyer/Gattermann-type transformations
Accurate depiction of carbocation stability and Markovnikov/anti-Markovnikov regioselectivity in alkene bromination
Proper arrow-pushing mechanisms showing intermediates: cyclic bromonium ions, enolates, tetrahedral intermediates
Stereochemical analysis for β-hydroxy carbonyl formation: syn/anti aldol products, racemic mixtures, and crossed aldol possibilities
Logical synthetic sequence for benzonitrile: nitration → reduction → diazotization → Sandmeyer cyanation or Rosenmund-von Braun alternative

Evaluation rubric

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	20%	10	Demonstrates precise understanding of reaction types, correctly identifies electrophilic/nucleophilic character, and applies concepts like HSAB principle, Baldwin's rules, and Saytzeff/Zaitsev preferences where relevant	Identifies most reactions correctly but confuses SN1/SN2 or E1/E2 distinctions, or misapplies regioselectivity rules in alkene additions	Fundamental misconceptions: treats all carbonyl additions as irreversible, confuses kinetic/thermodynamic enolates, or misidentifies reaction classes entirely
Mechanism / equation	25%	12.5	Complete curved-arrow mechanisms with all intermediates explicitly drawn, proper stereochemistry at each step, and balanced equations with correct stoichiometry for multi-step sequences	Mechanisms shown with some arrow errors or missing intermediates; equations balanced but omitting solvent participation or counter-ions	Incomplete mechanisms, incorrect arrow directions, missing crucial steps like deprotonation, or unbalanced equations with incorrect products
Numerical accuracy	15%	7.5	Correctly calculates theoretical yield of β-hydroxy carbonyl stereoisomers (2^n analysis), applies Hammett σ-ρ relationships for rate ordering, and gives precise stoichiometric coefficients	Correct enumeration of products but without stereochemical justification, or correct rate order with incorrect reasoning about substituent effects	Arbitrary numbers without calculation basis, incorrect counting of stereoisomers, or rate orders contradicting electronic effects
Diagram / structure	25%	12.5	Clean structural formulas with wedge-dash stereochemistry, chair conformations where relevant, resonance structures for intermediates, and clear distinction between starting materials, reagents, and products	Structures drawn but with ambiguous stereochemistry, missing formal charges on intermediates, or condensed formulas where expanded structures are needed	Illegible structures, incorrect connectivity, missing functional groups, or failure to distinguish isomers in product mixtures
Application context	15%	7.5	Cites industrial relevance: bromination in pharmaceutical synthesis (e.g., ibuprofen intermediates), aldol in perfumery (jasminaldehyde), and benzonitrile in Indian dye industry (Mumbai/Pithampur manufacturing hubs)	Generic mention of synthetic utility without specific industrial or Indian context, or relevant but unexplained applications	No application context provided, or factually incorrect associations between reactions and their real-world uses

Practice this exact question

Write your answer, then get a detailed evaluation from our AI trained on UPSC's answer-writing standards. Free first evaluation — no signup needed to start.

Evaluate my answer →