Question

SOLVED PROBLEM 7-3 When the following compound is heated in methanol, several different products are formed. Propose mechanisms to account for the four products shown. CH-Br CH heat CH,OH -OCH; + -OCH PARTIAL SOLUTION With no strong base and a good ionizing solvent, we would expect a first-order reaction. But this is a primary alkyl halide, so ionization is difficult unless it rearranges. It might rearrange as it forms, but we'll imagine the cation forming then rearranging. H. Br: CH CH heat (hydride shift) H.C-C СН,ОН TH HC-CH H_C-CH2 TH W. CH CH 10 carbocation 3 carbocation HH нс (alkyl shift] HC *C H - H-CC-H [HẠC-CH, HC-CH; H-C--H HH 1° carbocation 2° carbocation From these rearranged intermediates, either loss of a proton (El) or attack by the solvent ( SI) gives the observed products. Note that the actual reaction may give more than just these products, but the other products are not required for the problem. [ HC- CH] H PROBLEM 7-18 Finish Solved Problem 7-3 by showing how the rearranged carbocations give the four prod. ucts shown in the problem. Be careful when using curved arrows to show deprotonation and/or nucleophilic attack by the solvent. The curved arrows always show movement of electrons, not movement of protons or other species.

Answer 1

solution: The given reaction is (H₂-Br CH3 heat Снзон OCH, Mechanism. In this reaction no strong buse and polar aprotic solvent.. The solvent is polar protc. Thus the under go might be E or SNI mechanism, and not SN² and E, mechanism. CH₂ - Br. heat , CHA 7 hydride T Shift CH₃OH H₂C - I MC -cZH 4- CH₂ c Shift he CH₂ I carbocation 3 carbocation [ Heleng at alkyl shift CH2 ĄC CH2 Hi @CH I carbocation - CH₂ 2 carbocation heat in CH3OH it forms I carbocation. The i carbocution is unstable thus it under goes hydride shift to give 3 carbocation. It is more stable than 1 carbocation because electron donating effect (II) of alkyl group. → The i carbocation under ques alkyl (1,2 alkyl shift) shift to give 2 carbocation. It is more stable than 1 carbocation because I effect of alkyl group. The stability of carbocation is

OCH, 7 E, elimination нс - не нс — сна + ио- си, + сиз не CH, SNt reaction но си fo - CH2 Нc — с 1 Неси, + но си, 1. си, и, си. H . Ex elimination өсн + Hр- сна + СНа-он, HR с Н . SNA о - сизно - сна вси + + 40 - сна HC CH₂ о сиз Reaction ① and ② under goes Es pathway are elimination unimolecular. > Reaction @ e 4 under goes SN pathway de substitution nucleophilic unimolecular-