1. © Prentice Hall 2001Chapter 101 On Line Course Evaluation for Chemistry 350/Section 26260 We are participating in the online course evaluation Please log on http://web.utk.edu/~SAIS/http://web.utk.edu/~SAIS/ Click on Spring 2003 Evaluation That will take you to http://ecommerce.cas.utk.edu/SAIS/NetI Dinput.asp http://ecommerce.cas.utk.edu/SAIS/NetI Dinput.asp Your password is your email address

2. © Prentice Hall 2001Chapter 102 Williamson Ether Synthesis The Williamson ether synthesis is a good way to prepare ethers

3. © Prentice Hall 2001Chapter 103 Williamson Ether Synthesis This reaction is an S N 2 reaction and therefore benefits from a high concentration of alkoxide ion

4. © Prentice Hall 2001Chapter 104 Williamson Ether Synthesis The alkoxide ion is prepared by using sodium metal or sodium hydride to remove a proton from an alcohol

5. © Prentice Hall 2001Chapter 105 Williamson Ether Synthesis If you want to synthesize butyl propyl ether you have a choice of starting materials

6. © Prentice Hall 2001Chapter 106 Williamson Ether Synthesis If you want to prepare tert-butyl ethyl ether the starting materials must be an ethyl halide and tert-butoxide ion ethyl bromide tert-butoxide tert-butyl ethyl ethene ion ether

7. © Prentice Hall 2001Chapter 107 Williamson Ether Synthesis When ethoxide ion and tert-butyl bromide are used, only the elimination product is produced ethoxide ion tert-butyl bromide 2-methylpropene

8. © Prentice Hall 2001Chapter 108 Substitution and Elimination Reactions in Synthesis S N 1/E1 conditions are rarely useful synthetically

9. © Prentice Hall 2001Chapter 109 Designing a Synthesis II For simple syntheses it is possible to look at the starting material and see if there is any obvious pathway to the target molecule

10. © Prentice Hall 2001Chapter 1010 Designing a Synthesis II The only reaction available to an alkane is halogenation

11. © Prentice Hall 2001Chapter 1011 Designing a Synthesis II An E2 reaction with a high concentration of a strong bulky base should ensure elimination in favor of substitution

12. © Prentice Hall 2001Chapter 1012 Designing a Synthesis II Bromination of the cyclohexene then should give an allylic bromide which can be subjected to another E2 reaction Overall

13. © Prentice Hall 2001Chapter 1013 Designing a Synthesis II How would you carry out the following?

14. © Prentice Hall 2001Chapter 1014 Designing a Synthesis II Bromination would add selectively to the tertiary carbon Under E2 conditions a tertiary halide would yield only the elimination product

15. © Prentice Hall 2001Chapter 1015 Designing a Synthesis II We know also that Br 2 addition to an alkene yields only the anti product Overall we might propose:

16. © Prentice Hall 2001Chapter 1016 Designing a Synthesis II Retrosynthetic analysis is useful for more complex syntheses

17. © Prentice Hall 2001Chapter 1017 Designing a Synthesis II Only method we know to prepare a ketone is to add water to an alkyne

18. © Prentice Hall 2001Chapter 1018 Designing a Synthesis II The alkyne can be prepared by two successive E2 reactions on a vicinal dihalide

19. © Prentice Hall 2001Chapter 1019 Designing a Synthesis II The vicinal dihalide can be prepared via halogenation of an alkene

20. © Prentice Hall 2001Chapter 1020 Designing a Synthesis II The alkene can be prepared from the starting material via dehydrohalogenation

21. © Prentice Hall 2001Chapter 1021 Designing a Synthesis II From this analysis we might suggest the following synthesis: