UPSC Civil Services (Mains), Chemistry optional · 2022 · Paper II
Q8(b)(i). λmax of two polyenes by Woodward–Fieser rules
Question
Calculate the λmax values of the following compounds (1) and (2). [structures of two steroidal polyenes given in the paper]
Answer in brief
(1) λmax = 253 + 60 + 25 + 15 = 353 nm; (2) λmax = 214 + 30 + 20 + 10 = 274 nm.
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CoversWoodward–Fieser rulesλmax calculationhomoannular dieneheteroannular dieneUV spectroscopy
All parts of Question 8
- 8(a)(i) Carbonyl stretching frequency of two acetylcyclohexenes5 marks
- 8(a)(ii) Dehydration of 1,2-dimethylcyclohexanol; telling the alkenes apart by IR10 marks
- 8(b)(i) λmax of two polyenes by Woodward–Fieser rules10 marks
- 8(b)(ii) λmax of 1,3-butadiene and 1,3,5-hexatriene5 marks
- 8(c)(i) McLafferty rearrangement; fragmentation of butyl butyrate10 marks
- 8(c)(ii) C₂H₂BrCl with J = 16 Hz; two dienones from UV data10 marks