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 “antiMarkovnikov” 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