第六章常见反应机理精选文档.ppt
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1、第六章常见反应机理本讲稿第一页,共五十一页Step 1:Chain initiation:formation of radicals from nonradical speciesStep 2:Step 3:Chain propagation:reaction of radicals and a molecules to form a new radical1.1 Alkane halogenation reaction1.A Radical Chain Mechanism本讲稿第二页,共五十一页Chain termination(Destruction of radicals):Dispro
2、portionationCoupling本讲稿第三页,共五十一页Bond dissociation energy(kJ/mol)本讲稿第四页,共五十一页Enthalpy change H?Entropy change S?Free energy change G?本讲稿第五页,共五十一页How about the chlorination of methane?How about the bromination of propene?Activity:FClBrI;Allyl,3 2 1Selectivity:FClBr 2 1本讲稿第六页,共五十一页1.2 Radial Oxidation
3、with Oxygen Chain initiationChain propagation本讲稿第七页,共五十一页Draw a mechanism for the following reaction本讲稿第八页,共五十一页1.3.Radical addition reactionInitiationPropagationH-O 428H-Cl 432H-Br 368C-Br 272,H-Cl 432,H-C 403,pi键键682368本讲稿第九页,共五十一页2.Electrophilic addition to C,C multiple bonds2.1.Carbocation mecha
4、nismDirection:The more stable carbocation form preferentially Caution:Carbocation rearrangement!本讲稿第十页,共五十一页本讲稿第十一页,共五十一页2.2.Nium reaction mechanismminor contributing structureSterospecificity:Anti addition本讲稿第十二页,共五十一页The electronegativity tell you which one is E+.本讲稿第十三页,共五十一页2.3.Oxymercuration-Re
5、duction本讲稿第十四页,共五十一页A bridged mercurinium:three-center/two-electron bond本讲稿第十五页,共五十一页3.Nucleophilic addition to C,C multiple bonds本讲稿第十六页,共五十一页4.Concerted addition to C,C multiple bondsA syn addition mechanism4.1.Catalytic hydrogenation本讲稿第十七页,共五十一页4.2.Hydroboration-Oxidation本讲稿第十八页,共五十一页本讲稿第十九页,共五十
6、一页4.3.OsO4-OxidationCatalytic amount OsO4(expensive and highly toxic)with peroxide本讲稿第二十页,共五十一页4.4.KMnO4-Oxidation本讲稿第二十一页,共五十一页4.5.Diels-Alder reaction本讲稿第二十二页,共五十一页Overlap between the highest occupied MO of the diene(HOMO)and the lowest unoccupied MO of the dienophile(LUMO)is thermally allowed in
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