Organic Chemistry

1. Organic Chemistry Chapter 10

2. Functional Groups

3. The Key To Substitution Reactions • The Leaving Group Goes

4. Substitution Rx of R-OH • Alcohols have polar groups which make substitution probable • Alcohols have a strongly basic leaving group (OH-) which make it not probable • Protonationconverts an alcohol to a good leaving group

5. Mechanisms • Wow… we get to draw one…….. From yahoo images

6. Substitution Rx of R-OH • HBr and HI work well for SN2 reactions. • HCl does not work well because Cl is a poorer nucleophile. • Rate can be increased using ZnCl2 • Zn2+ is a Lewis Acid • Complexes with the O: • (this weakens the C-O bond)

7. Lucas Test • .

8. Rearramgement • OH ya, don’t forget -

9. “Grain” and “Wood Alcohol” • .

10. Conversion of Alcohols • Use phosphorous trihalides or thionyl chloride • Better yields and no rearrangements • PCl3, PBr3, PI3, or SOCl2 Do the Mechanism…………………….. From yahoo images

11. Conversion of Alcohols Pyridine is used as the solvent because it prevents formation of HCl or HBr and is a poor nucleophile.

12. D D D pyridine pyridine pyridine Conversion of Alcohols • Commonly Used Methods for Converting Alcohols into Alkyl Halides • ROH + HBr RBr • ROH + HI RI • ROH + HCl RCl • ROH + PBr3 RBr • ROH + PCl3 RCl • ROH + SOCl2 RCl

13. Sulfonate esters leaving groups • Conversion of alcohols to sulfonyl chlorides • p-toluenesulfonyl chloride (tosyl chloride, TsCl) • methylsulfonyl chloride (mesyl chloride, MsCl) • trifluoromethanesulfonyl chloride (trif) • They are up to 100 x better than Cl-as leaving groups

14. Sulfonic acid has apKa of – 6.5 wow!! That ought to be on stable base now don’t ya think?

15. Reaction steps

16. Dehydration of Alcohols • Zaitsev’s Rule – more substituted formed

17. Dehydration of Alcohols • Dehydration is the reverse of Hydration • vary conditions to control equilibrium • Remove the alkene by distillation

18. Dehydration of Alcohols • Reaction may involve rearrangement

19. Dehydration of Alcohols • rearrangements with ring opening

20. Dehydration of Alcohols E and Z produced, major product will have most bulky groups on opposite sides

21. Dehydration with POCl3 • Uses a better leaving group • Conditions are not as extreme • Phosphorous oxychloride and pyridine • No rearrangements • Mildly basic conditions favor E2

22. Oxidation of Alcohols Look at reaction and conditions For Primary and Secondary Alcohols From yahoo images

23. Substitution Rx of Ethers • Ethers can be activated by acid • High concentration of HI, HBr will form the alkyl halide

24. Ethers as Solvents • Ethers are relatively unreactive so they are frequently used as solvents • diethyl ether (ether) • tetrahydrofuran (THF) • 1,4-dioxane • 1,2-dimethoxyethane (DME) • methyl t-butyl ether (MTBE)

25. Addition of Peroxyacids ...from chapter 4... • Alkenes can be oxidized to an epoxide by a peroxyacid.

26. Reactions of Epoxides • Because of 3 membered ring, epoxides are much more reactive than normal ethers • Undergo ring opening reactions at room temp

27. Reactions of Epoxides(oxiranes) Formation of glycols (addition of H2O)

28. Reactions of Epoxides(oxiranes)) Unsymmetrical additions yield the product resulting from Nu: attack on the more substituted carbon

29. Reactions of Epoxides(oxiranes) Under basic conditions, Nu: attack is at the less hindered C The epoxide is reactive enough that you don’t need to protinate to get the reaction to go

30. Crown Ethers

31. Crown Ethers • Cyclic compounds with ether linkages • Bind cations as “host” and “guest”

32. Crown Ethers • Naming – [x]-crown-Y • X = total number of atoms in the ring • Y = total number of oxygens

33. Thiols and Sulfides

34. Thiols and Sulfides • Thiols are sulfur analogs of alcohols • Also called mercaptans (mercury capturing)

35. Thiols and Sulfides • Thiols are named by adding suffix “thiol” • Remember to keep the e • Common names are alkyl mercaptans

36. Physical Properties-Thiols • The difference in electronegativity between S (2.5) and H (2.1) is 0.4. • This creates a bond with low polarity • show little association by hydrogen bonding • have lower boiling points and are less soluble in water than alcohols of comparable MW

37. Thiols act as Nucleophiles • Thiolate anions are weak bases (weaker than alkoxides) and in protic solvents are better nucleophiles (better than alkoxides since they don’t H bond)

38. Sulfides or thioethers • Sulfur analogs are called sulfides or thioethers • Most sulfides react readily to form sulfonium salts

39. Sulfides or thioethers • The sulfonium salt easily reacts in a substitution reaction:

41. Organometallic Compounds So far, we have seen reaction in which carbon is bonded to a more electronegative atom. What happens when it is connected to a less electronegative atom?

42. Organometallic Compounds A compound that contains a carbon-metal bond Organolithium Organomagnesium (Grignard Reagent)

43. Organometallic Compounds

44. Organometallic Compounds Organometalics act as nucleophiles Reactions must be carried out in very dry solvents and nothing acidic Can be in the reaction mixture

45. Organometallic Compounds The greater the polarity difference, the greater the reactivity of an organometalic reagent

46. Coupling Reactions • Gilman Reaction • Heck Reaction • Stille Reaction • Suzuki Reaction

47. Henry Gilman 1893-1986 Gilman Reagents Prepared from an organolithium reagent and copper(I) iodide

48. Henry Gilman 1893-1986 Gilman Reagents • Gilman reagents can be used to form new carbon-carbon bonds by cross-coupling with alkyl oraryl or vinylic halides (Note: cannot use SN2 with aryl or vinylic halides)

49. The Heck Reaction

50. The Stille Reaction