Indian Forest Service (Mains), Chemistry optional · 2021 · Paper II

Q2(d)(i). Elimination of 2-bromobutane

5 marks
Topic: Elimination reactions
Answered

Question

Give the reaction of 2-bromobutane with alcoholic KOH, justify the major alkene stereochemistry, and state the coupling constant of its olefinic protons.

Answer in brief

Hot alcoholic KOH gives mainly (E)-but-2-ene, with (Z)-but-2-ene and but-1-ene as minor products; the trans vicinal coupling is typically about 15–16 Hz.

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Topic notes: elimination reactions (E1, E2, E1cB, Saytzeff and Hofmann, anti-periplanar, Chugaev, Cope), with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversE2 eliminationZaitsev rule2-bromobutanetrans-but-2-enevicinal coupling constant

All parts of Question 2

2(a) Thermal closure of octatriene10 marks
2(b) Hydrolysis of tert-butyl chloride10 marks
2(c)(i) p-Toluidine to m-bromotoluene5 marks
2(c)(ii) Hofmann elimination5 marks
2(d)(i) Elimination of 2-bromobutane5 marks
2(d)(ii) Chalcone, cyanide addition and reduction5 marks