《国外有机化学》 英文版 Chapter 8 Reactions of Alkenes

organic Chemistry, 5th Edition C--CHun L.G. Wade Jr Chapter 8 Reactions of alkenes Jo blackburn Richland college, dallas TX Dallas County Community College District c 2003. Prentice hall

Chapter 8 Reactions of Alkenes Jo Blackburn Richland College, Dallas, TX Dallas County Community College District © 2003, Prentice Hall Organic Chemistry, 5th Edition L. G. Wade, Jr

Reactivity of C=C C Electrons in pi bond are loosely held Electrophiles are attracted to the pi electrons Carbocation intermediate forms Nucleophile adds to the carbocation Net result is addition to the double bond > Chapter 8

Chapter 8 2 Reactivity of C=C • Electrons in pi bond are loosely held. • Electrophiles are attracted to the pi electrons. • Carbocation intermediate forms. • Nucleophile adds to the carbocation. • Net result is addition to the double bond. =>

Electrophilic Addition C Step 1: Pi electrons attack the electrophile E C+ Step 2: Nucleophile attacks the carbocation E E Nuc -C-C+ t Nuc C-C hapter 8

Chapter 8 3 Electrophilic Addition • Step 1: Pi electrons attack the electrophile. C C + E + C E C + C E C + + Nuc: _ C E C Nuc => • Step 2: Nucleophile attacks the carbocation

Types of Additions f Addition Product Elements Added] H OH ation halogenation H,OJ TX2 an oxidation OH hydrogenation halohydrin formtion [H,I, a reduction [HOXI, an oxidation OH OH hydroxyl at ion HX addition HOOH I. an oxidation HXI oxidative cle C=00= [O,I an oxidation cyclopropanation epoxidat ion CH, O. an oxidation a These are not the reagents used but simply the groups that appear in the product

Chapter 8 4 Types of Additions =>

Addition of HX(1) C Protonation of double bond yields the most stable carbocation Positive charge goes to the carbon that was not protonated CH3 CH3-C-CH-CH3 CH3-C-CH-CH3 Br Br X CH3 CH3-C-CH--CH3 十 > Chapter 8

Chapter 8 5 Addition of HX (1) Protonation of double bond yields the most stable carbocation. Positive charge goes to the carbon that was not protonated. X => + Br _ + + CH3 C CH3 CH CH3 H CH3 C CH3 CH CH3 H H Br CH3 C CH3 CH CH3

Addition of HX (2 C CH CH CH3-C=CH-CH3 CH3-C--CH-CH3 Br 十 H-Br C CH3-C--CH-CH3 CH3-C-CH-CH3 > Br h Bra Chapter 8

Chapter 8 6 Addition of HX (2) CH3 C CH3 CH CH3 H Br CH3 C CH3 CH CH3 H + + Br _ CH3 C CH3 CH CH3 H + Br _ CH3 C CH3 CH CH3 Br H =>

Regiospecificity C Markovnikov' s Rule: The proton of an acid adds to the carbon in the double bond that already has the most H's. Rich get richer” More general Markovnikov's Rule: In an electrophilic addition to an alkene, the electrophile adds in such a way as to form the most stable intermediate HCL HBr and hi add to alkenes to form Markovnikov products Chapter 8

Chapter 8 7 Regiospecificity • Markovnikov’s Rule: The proton of an acid adds to the carbon in the double bond that already has the most H’s. “Rich get richer.” • More general Markovnikov’s Rule: In an electrophilic addition to an alkene, the electrophile adds in such a way as to form the most stable intermediate. • HCl, HBr, and HI add to alkenes to form Markovnikov products. =>

Free-Radical Addition of hbr C In the presence of peroxides, HBr adds to an alkene to form the anti Markovnikov"product Only HBr has the right bond energy ·HC| bond is too strong HI bond tends to break heterolytically to form ions Chapter 8

Chapter 8 8 Free-Radical Addition of HBr • In the presence of peroxides, HBr adds to an alkene to form the “anti￾Markovnikov” product. • Only HBr has the right bond energy. • HCl bond is too strong. • HI bond tends to break heterolytically to form ions. =>

Free Radical Initiation c-Cu Peroxide o-o bond breaks easily to form free radicals heat R-0-0-R R-0·+·O-R Hydrogen is abstracted from hBr R-0·+H÷Br R-o-H Br hapter 8 Electrophile

Chapter 8 9 Free Radical Initiation • Peroxide O-O bond breaks easily to form free radicals. R O + H Br R O H + Br R O O R R O + O R heat • Hydrogen is abstracted from HBr. Electrophile =>

Propagation Steps C Bromine adds to the double bond Br Br Hydrogen is abstracted from Hbr C +"ⅡBr t Br Br Br h hapter 8 Electrophile=>10

Chapter 8 10 Propagation Steps • Bromine adds to the double bond. + C Br C + H Br C Br C H Br Electrophile => C Br Br C C C + • Hydrogen is abstracted from HBr