(a) (i) Complete the following reaction by showing stepwise reaction mechanism for the formation of products :

(ii) The compound A is optically active and upon treating A with alcoholic sodium ethoxide, it looses its optical activity. Justify :

(b)

Question

(a) (i) Complete the following reaction by showing stepwise reaction mechanism for the formation of products :

(ii) The compound A is optically active and upon treating A with alcoholic sodium ethoxide, it looses its optical activity. Justify :

(b) (i) If more than one equivalent of Br₂ at high temperature are allowed to react with cyclopentane, how many dibromocyclopentanes would you expect as products? Draw their structures and name them.

(ii) How will you convert p-nitrotoluene to m-nitrotoluene?

(c) By using appropriate reagents and conditions, how will you convert phenol into coumarin? Give suitable mechanism for this transformation.

UPSC Answer Check · Accepted Answer

Begin with a brief introduction acknowledging the diverse reaction types covered. For part (a), spend ~25% time on mechanism with curved arrows and stereochemistry; for (b)(i), allocate ~20% on systematic enumeration of dibromo isomers with clear naming; for (b)(ii), devote ~15% on the diazotization route with positional control; for (c), reserve ~40% on the Pechmann condensation mechanism with all intermediates. Conclude by summarizing the synthetic strategies employed.
- Part (a)(i): Complete stepwise mechanism showing carbocation formation, rearrangement if any, and nucleophilic attack with proper curved arrow notation
- Part (a)(ii): Explanation of racemization via SN1/SN2/E2 pathway with formation of planar intermediate or elimination leading to achiral product
- Part (b)(i): Enumeration of all dibromocyclopentane stereoisomers (1,1-; 1,2-cis/trans; 1,3-cis/trans) with correct IUPAC names including stereodescriptors
- Part (b)(ii): Synthetic route via nitration of toluene, oxidation to benzoic acid, nitration at meta position, then reduction and re-oxidation OR diazotization-based approach
- Part (c): Pechmann condensation using malic acid/sulfuric acid or Knoevenagel-type condensation with β-keto ester, showing all mechanistic steps including electrophilic aromatic substitution and lactonization
- Stereochemical analysis: Identification of meso compounds, enantiomeric pairs, and optical activity changes in relevant parts
- Reagent and condition specificity: Concentrated H₂SO₄, high temperature, alcoholic NaOEt, etc. with their mechanistic implications

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	22%	8	Demonstrates flawless understanding of carbocation stability, SN1/SN2/E2 competition, aromatic substitution orientation effects, and Perkin/Pechmann condensation chemistry; correctly identifies that 1,2-dibromocyclopentane has cis/trans stereoisomers and that 1,3-substitution pattern exists	Shows basic understanding of reaction types but confuses SN1/SN2 conditions, misidentifies some isomers, or makes minor errors in orientation rules for aromatic substitution	Fundamental misconceptions about mechanism types, incorrect orientation predictions, or failure to recognize stereochemical relationships in cyclopentane derivatives
Mechanism / equation	24%	8	All three required mechanisms (part a, part c, and implied in part b) shown with complete curved arrow notation, proper intermediate structures, and correct electron flow; includes deprotonation steps and regeneration of catalyst where applicable	Mechanisms shown but with missing curved arrows, incomplete intermediate depictions, or incorrect arrow directions; omits key steps like proton transfers	Mechanisms absent or fundamentally wrong with incorrect arrow placement, missing intermediates, or violation of basic mechanistic principles
Numerical accuracy	14%	5	Correctly counts 5 distinct dibromocyclopentane structures (1,1-; 1,2-cis; 1,2-trans; 1,3-cis; 1,3-trans) with proper accounting for enantiomers where relevant; accurate stoichiometric reasoning for 'more than one equivalent' condition	Identifies most isomers but misses one stereoisomer pair or confuses 1,2- and 1,3- substitution patterns; minor counting errors	Severely undercounts or overcounts isomers; fails to distinguish constitutional from stereoisomers; ignores stereochemistry entirely
Diagram / structure	22%	8	All structures drawn with correct stereochemistry (wedge/dash for chiral centers), proper ring conformations where relevant, clear numbering for IUPAC names, and unambiguous depiction of coumarin bicyclic system; 3D representation for optical activity discussion	Structures drawn but with inconsistent stereochemical notation, flat representations where 3D needed, or unclear connectivity; acceptable but not precise	Structures incorrect, missing, or chemically impossible; poor handwriting/line quality making structures ambiguous; no attempt at stereochemical representation
Application context	18%	6	Connects coumarin synthesis to natural product and pharmaceutical importance (warfarin, psoralens); explains why meta-nitration requires indirect route due to ortho/para directing methyl group; discusses industrial relevance of free radical bromination	Brief mention of application context without elaboration; standard textbook connections without synthesis of why these transformations matter synthetically	No application context provided; treats all reactions as purely academic exercises without real-world or synthetic planning relevance

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