1. The "peroxide effect" 6.8 Free-radical Addition of HBr to Alkenes

2. acetic acid Br CH 3 CH 2 CHCH 3 CH 2 CH 3 CH 2 CH HBr (80%) Markovnikov's Rule

3. only product in absence of peroxides CH 3 CH 2 CH 2 CH 2 Br only product when peroxides added to reaction mixture Br CH 3 CH 2 CHCH 3 CH 2 CH 3 CH 2 CH HBr Addition of HBr to 1-Butene

4. CH 3 CH 2 CH 2 CH 2 Br only product when peroxides added to reaction mixture CH 2 CH 3 CH 2 CH HBr addition opposite to Markovnikov's rule occurs with HBr (not HCl or HI) Addition of HBr to 1-Butene

5. Addition of HBr with a regiochemistry opposite to Markovnikov's rule can also occur when initiated with light with or without added peroxides. + HBr h (60%) CH 2 CH 2 Br H Photochemical Addition of HBr

6. Addition of HBr opposite to Markovnikov's rule proceeds by a free-radical chain mechanism. Initiation steps:.... OR R O.... O. R........OR. + Mechanism

7. Addition of HBr opposite to Markovnikov's rule proceeds by a free-radical chain mechanism. Initiation steps:.... OR R O....+ Br O. R........OR. + O. R....H.... : + O R.... H. Br....: Mechanism

8. Propagation steps: + CH 3 CH 2 CH CH 2. Br....:. CH 3 CH 2 CH CH 2 Br :.... Mechanism

9. Propagation steps: + + CH 3 CH 2 CH CH 2. Br....:. CH 3 CH 2 CH CH 2 Br :..... CH 3 CH 2 CH CH 2 Br :.... H Br....:.. CH 3 CH 2 CH 2 CH 2 Br:... Br....: Mechanism

10. 6.9 Addition of Sulfuric Acid to Alkenes

11. follows Markovnikov's rule: yields an alkyl hydrogen sulfate CH 3 CHCH 3 OSO 2 OH CH 3 CH CH 2 HOSO 2 OH Isopropyl hydrogen sulfate Addition of H 2 SO 4

12. + slow + fast CH 3 CH CH 2 H.. SO 2 OH.. + CH 3 CH CH 3.. SO 2 OH.. : – O O CH 3 CHCH 3 OSO 2 OH :.. Mechanism

13. H—OH HO—SO 2 OH + CH 3 CHCH 3 O SO 2 OH heat CH 3 CHCH 3 O H + Alkyl hydrogen sulfates undergo hydrolysis in hot water

14. 1. H 2 SO 4 2. H 2 O, heat (75%) Application: Conversion of alkenes to alcohols OH

15. not all alkenes yield alkyl hydrogen sulfates on reaction with sulfuric acid these do: H 2 C=CH 2, RCH=CH 2, and RCH=CHR' H 2 C=CH 2, RCH=CH 2, and RCH=CHR' these don't: R 2 C=CH 2, R 2 C=CH 2, and R 2 C=CR 2 But...