123.202 Lecture 10 - alkenes

1. ..LECTURE TEN the last ©gonzales2010@ﬂickr (mono)alkenes

2. PREVIOUSLY... diol formation HO OH KMnO4 H H

3. ozonolysis i. O3(g) ii. Zn/H2O O O cleaves alkenes

4. mechanismwell, the steps involved... O O O O O O O O Zn/H2O O O O

5. radical chemistry ©Renaissance Pictures

6. free radical to alkenes addition of HBr HBr ROOR H Br anti Markovnikov addition

7. mechanism step initiation O R 2x R O R O R O H Br O Br R H radical chain reaction

8. ‘curly fishhook’ a radical is one electron

9. ‘curly fishhook’ need two electrons to form a bond

10. mechanism step propagation Br Br H Br H Br Br Br

11. chain carrier Br

12. mechanism step termination Br Br Br Br Br Br Br Br

13. ©Oberazzi@ﬂickr

14. radical stability < < missing one electron

15. 11 HBr addition to styrenes H HBr Br Br we H known

16. but... H Ph HBr Ph Br single product

18. resonance stabilisation H Br H H H H Br benzylic cation H stable

19. NO resonance stabilisation H H Br

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