1、Chapter 6 Familiar reaction mechanisms1. A Radical Chain Mechanism2. Electrophilic addition to C,C multiple bonds3. Nucleophilic addition to C,C multiple bonds4. Concerted addition to C,C multiple bonds5. Substitution reactions6. Elimination reactions7. Name reactions,Step 1:,Chain initiation: forma
2、tion of radicals from nonradical species,Step 2:,Step 3:,Chain propagation: reaction of radicals and a molecules to form a new radical,1.1 Alkane halogenation reaction,1. A Radical Chain Mechanism,Chain termination (Destruction of radicals ):,Disproportionation,Coupling,Bond dissociation energy (kJ/
3、mol),Enthalpy change H ?Entropy change S ?Free energy change G ?,How about the chlorination of methane?How about the bromination of propene?,Activity: FClBrI; Allyl, 3 2 1,Selectivity: F 2 1,1.2 Radial Oxidation with Oxygen,Chain initiation,Chain propagation,Draw a mechanism for the following reacti
4、on,1.3. Radical addition reaction,Initiation,Propagation,H-O 428H-Cl 432H-Br 368,C-Br 272, H-Cl 432,H-C 403, pi键682368,2. Electrophilic addition to C,C multiple bonds,2.1. Carbocation mechanism,Direction: The more stable carbocation form preferentially,Caution: Carbocation rearrangement!,2.2. Nium r
5、eaction mechanism,minor contributing structure,Sterospecificity: Anti addition,The electronegativity tell you which one is E+.,2.3. Oxymercuration-Reduction,A bridged mercurinium: three-center/two-electron bond,3. Nucleophilic addition to C,C multiple bonds,4. Concerted addition to C,C multiple bond
6、sA syn addition mechanism,4.1. Catalytic hydrogenation,4.2. Hydroboration-Oxidation,4.3. OsO4-Oxidation,Catalytic amount OsO4 (expensive and highly toxic)with peroxide,4.4. KMnO4-Oxidation,4.5. Diels-Alder reaction,Overlap between the highest occupied MO of the diene (HOMO) and the lowest unoccupied
7、 MO of the dienophile (LUMO) is thermally allowed in 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.,There are “inverse demand” Diels Alder Reactions tha
8、t involve the overlap of the HOMO of the dienophile 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.,The endo product is usually favored by kinetic control due to secondary orbital interactions
9、.,The reaction is diastereoselective.,5. Substitution Reactions,5.1 Nuclephilic Substitution Reactions,SN1,SN2,SN1,SN2,Tertiary alkyl Primary alkylPoor nucleophile Good nucleophilePolar solvent Nonpolar solventGood Leaving group Poor leaving group,5.2 Electrophilic Aromatic Substitution Reactions,5.
10、3 Nucleophilic Aromatic Substitution Reactions,R= group with both -I and -C effects,6. Elimination reactions,E1,E2,E1cb,Saytzeff rule,Hofmann rule,Hofmann rule,-branches results in Hofmann product,7. Name Reactions7.1. Aldol condensation,7.2. Arndt-Eistert Synthesis-Wolff rearrangement,7.3. Benzoin
11、Condensation,X. Linghu, J. S. Johnson, Angew. Chem., 2003, 115, 2638,Key Intermediate:,7.4. Claisen Condensation,Key Intermediate:,Dieckmann Condensation,7.5. Cannizzaro Reaction,7.6. Diazotisation,7.7. Haloform Reaction,7.8. Hell-Volhard-Zelinsky Reaction,7.9. Mannich Reaction,7.10. Michael Addition,donors,acceptors,7.11. Arbuzov ReactionMichaelis-Arbuzov Reaction,7.12. Reformatsky Reaction,7.13. Wolff-Kishner Reduction,
