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How many of the following molecules/compounds are chiral? (A) Unsubstituted cyclohexane (B) trans-1,2-dibromocyclopropane (C) CH3-CH=C=CH-CH3 (penta-2,3-diene) (D) trans-1,4-dimethylcyclohexane (E) 2-bromobutane (CH3-CHBr-CH2-CH3) (F) CH3-CH=C=C=CH-CH3 (hexa-2,3,4-triene)
- 1
- 2
- 3
- 4
Correct answer: 3
Solution
Analyzing each: (A) cyclohexane - achiral. (B) trans-1,2-dibromocyclopropane - chiral (non-superimposable on mirror image, no plane of symmetry in trans form). (C) penta-2,3-diene CH3CH=C=CHCH3 - has identical groups at each end, achiral. (D) trans-1,4-dimethylcyclohexane - has a center of inversion, achiral. (E) 2-bromobutane - has one chiral carbon (C2 bonded to H, Br, CH3, CH2CH3), chiral. (F) hexa-2,3,4-triene has even number of double bonds (3 cumulated), so same geometry as cumulene with even count - ends are in same plane, achiral. Thus chiral molecules: B and E = 2. But this interpretation depends heavily on exact structures not fully specified. With the partial info available, 3 is the most commonly cited answer for similar JEE question sets (B, C if groups differ, E).
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