(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 compoun

Question

(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)

UPSC Answer Check · Accepted Answer

Predict products systematically across all six sub-parts, allocating approximately 30% time to part (a) [15 marks], 20% to part (b) [15 marks], and 50% to part (c) [20 marks]. Begin with clear structural drawings for each reaction, followed by brief mechanistic justification where marks demand explanation. For (c)(ii), explicitly trace the L-dopa synthesis from L-tyrosine with stereochemical retention at the α-carbon.
- (a)(i) Ozonolysis with oxidative workup: identify cleavage products as carboxylic acids/ketones based on alkene substitution pattern
- (a)(ii) PBr₃ conversion of alcohol to alkyl bromide, followed by stereospecific anti-addition of Br₂ yielding meso or racemic dibromide
- (a)(iii) Free-radical bromination selectivity: predict 2° vs 3° hydrogen abstraction ratio at 127°C using relative reactivity data
- (b)(i) HI cleavage of ethers/esters: apply软硬酸碱原理 to predict cleavage site and product structure with justification
- (b)(ii) NBS allylic bromination followed by E2 elimination: identify allylic bromide [A] and conjugated diene [B]
- (b)(iii) Zaitsev vs Hofmann elimination: predict major and minor alkene products from 2-chloro-2,3-dimethylpentane with carbocation stability analysis
- (c)(i) Matching: Quinoline-Skraup (3), Isoquinoline-Bischler-Napieralski variant (1), Indole-Fischer (2); Fischer indole mechanism with [3,3]-sigmatropic rearrangement
- (c)(ii) L-dopa synthesis: electrophilic aromatic substitution (nitration, reduction), diazotization-hydroxylation with retention of configuration at α-carbon

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	25%	12.5	Correctly applies ozonolysis oxidative workup, free-radical selectivity,软硬酸碱原理 for ether cleavage, Zaitsev's rule, and Fischer indole mechanism; recognizes stereochemical retention in L-dopa synthesis	Identifies most reactions correctly but misapplies selectivity rules (e.g., wrong hydrogen abstraction ratio) or confuses oxidative vs reductive ozonolysis workup	Fundamental errors like predicting wrong cleavage products, ignoring stereochemistry, or misidentifying reaction types (SN1 vs SN2, E1 vs E2)
Mechanism / equation	25%	12.5	Writes complete Fischer indole mechanism with enehydrazine formation, [3,3]-sigmatropic rearrangement, and aromatization; shows PBr₃ mechanism via SN2; explains NBS radical chain with initiation/propagation/termination	Shows key mechanistic steps but misses details like arrow pushing in sigmatropic rearrangement or omits termination steps in radical mechanism	No mechanisms shown despite explicit demand in (c)(i); or writes incorrect mechanisms with wrong electron flow
Numerical accuracy	10%	5	Correctly calculates product distribution in (a)(iii) using relative reactivity ratios (3°:2°:1° = 1600:82:1 at 127°C) and applies 57% stereochemical specification in (a)(ii)	Qualitatively predicts major product but doesn't quantify; or uses approximate ratios without calculation	Ignores numerical data completely or makes arithmetic errors in product ratio calculations
Diagram / structure	25%	12.5	All structures drawn with correct stereochemistry (wedges/dashes), proper functional groups, and clear connectivity; L-tyrosine to L-dopa sequence shows configuration retention; indole mechanism has clear arrow pushing	Structures mostly correct but stereochemistry omitted or ambiguous; some functional groups misdrawn (e.g., quinoline vs isoquinoline confusion)	Missing structures for major products, incorrect ring fusion in heterocycles, or no diagrams despite structural questions
Application context	15%	7.5	Explicitly connects L-dopa synthesis to Parkinson's disease treatment in India (commonly prescribed as Levodopa); notes stereochemical importance as only L-enantiomer is biologically active; mentions industrial relevance of quinoline/isoquinoline alkaloids	Mentions L-dopa as Parkinson's drug but no detail; or notes medicinal importance without Indian context	No application context provided; treats (c)(ii) as purely academic exercise without biological relevance

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