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

7、the Diels Alder Reaction,provided the orbitals are of similar energy.The reaction is facilitated by electron-withdrawing groups on the dienophile,since this will lower the energy of the LUMO.本讲稿第二十三页，共五十一页 There are“inverse demand”Diels Alder Reactions that involve the overlap of the HOMO of the die

8、nophile with the LUMO of the diene.This alternative scenario for the reaction is favored by electron-donating groups on the dienophile and an electron-poor diene.本讲稿第二十四页，共五十一页The endo product is usually favored by kinetic control due to secondary orbital interactions.本讲稿第二十五页，共五十一页The reaction is d

9、iastereoselective.本讲稿第二十六页，共五十一页5.Substitution Reactions5.1 Nuclephilic Substitution ReactionsSN1SN2本讲稿第二十七页，共五十一页SN1SN2Tertiary alkyl Primary alkylPoor nucleophile Good nucleophilePolar solvent Nonpolar solventGood Leaving group Poor leaving group本讲稿第二十八页，共五十一页5.2 Electrophilic Aromatic Substitutio

10、n Reactions本讲稿第二十九页，共五十一页5.3 Nucleophilic Aromatic Substitution ReactionsR=group with both-I and-C effects本讲稿第三十页，共五十一页6.Elimination reactionsE1E2E1cbSaytzeff ruleHofmann rule本讲稿第三十一页，共五十一页Hofmann rule本讲稿第三十二页，共五十一页-branches results in Hofmann product本讲稿第三十三页，共五十一页本讲稿第三十四页，共五十一页7.Name Reactions7.1.A

11、ldol condensation本讲稿第三十五页，共五十一页7.2.Arndt-Eistert Synthesis-Wolff rearrangement 本讲稿第三十六页，共五十一页7.3.Benzoin Condensation本讲稿第三十七页，共五十一页X.Linghu,J.S.Johnson,Angew.Chem.,2003,115,2638Key Intermediate:本讲稿第三十八页，共五十一页7.4.Claisen Condensation Key Intermediate:本讲稿第三十九页，共五十一页Dieckmann Condensation本讲稿第四十页，共五十一页7

12、.5.Cannizzaro Reaction本讲稿第四十一页，共五十一页7.6.Diazotisation本讲稿第四十二页，共五十一页7.7.Haloform Reaction 本讲稿第四十三页，共五十一页7.8.Hell-Volhard-Zelinsky Reaction本讲稿第四十四页，共五十一页本讲稿第四十五页，共五十一页7.9.Mannich Reaction本讲稿第四十六页，共五十一页7.10.Michael Additiondonors acceptors 本讲稿第四十七页，共五十一页7.11.Arbuzov ReactionMichaelis-Arbuzov Reaction本讲稿第四十八页，共五十一页7.12.Reformatsky Reaction本讲稿第四十九页，共五十一页7.13.Wolff-Kishner Reduction本讲稿第五十页，共五十一页本讲稿第五十一页，共五十一页