Chapter9

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Chapter9

  1. 1. Chapter 9 Spring 2009
  2. 3. Alcohol nomenclature using IUPAC rules <ul><li>Step 1 Name the longest carbon chain containing the –OH. Change the –e ending to the suffix –ol. </li></ul><ul><li>Step 2 Number the carbon chain to give the –OH group the lower number, and apply all other rules of nomenclature. </li></ul>
  3. 4. Step 1: The longest carbon chain above is 5 carbons long, therefore, the base name of the molecule is pentanol. Step 2: The molecule should be numbered from right to left, placing the –OH group on C2, and the methyl groups on C3 and C4. The name is thus, 3,4-dimethyl-2-pentanol .
  4. 5. Naming cyclic alcohols The –OH group is assigned the C1 position. The second substituent then gets the lowest number. The name of the compound is 3-isopropyl-cyclopentanol
  5. 7. 4-ethyl-3-isopropyl-2-heptanol 2-ethyl-5,5-dimethylcyclohexanol
  6. 8. When an alcohol is a substituent
  7. 9. When an alcohol is a substituent 3-(2-hydroxyethyl)cyclohexanol
  8. 10. Ether nomenclature using IUPAC rules <ul><li>Name the simpler alkyl group + O atom as an alkoxy substituent by changing the –yl ending of the alkyll group to –oxy. (examples on next page) </li></ul><ul><li>Name the remaining alkyl group as an alkane, with the alkoxy group as a substituent bonded to this chain </li></ul>
  9. 11. Common alkoxy groups
  10. 12. 1. Name the longer chain as the alkane and the shorter chain as the alkoxy group Above the longest chain is a hexane. Longest chain 2. Use IUPAC rules to finish the name. The substituent should have the smallest number possible. Thus, number from right to left. 3-methoxyhexane methoxy
  11. 14. 2-methyl-1-ethoxycyclopentane 1-butoxy-2,2-dimethylhexane
  12. 15. Cyclic ethers
  13. 16. Naming epoxides This is oxirane – the simplest epoxide These are named as substituted oxiranes 1,2-dimethyloxirane 1,1-dimethyloxirane To name an epoxide as a substituent, it is called an epoxy. This is then 1,2-epoxycyclohexane
  14. 17. Preparation of alcohols and ethers
  15. 18. The nucleophile <ul><li>OH - is commonly supplied as NaOH or KOH </li></ul><ul><li>The alkoxide is most commonly generated from its corresponding alcohol. </li></ul>
  16. 19. Draw the product of the following two-step sequence [1] In the first step the base NaH removes the proton from the alcohol [2] In the second step of the process the alkoxide acts as a nucleophile displacing the leaving group in an S N 2 reaction
  17. 20. Preparation of epoxides Starting reagent is a halohydrin Two-step process:
  18. 21. Reactions of… <ul><li>Alcohols </li></ul><ul><li>Dehydration – elimination of –OH and –H from an α and β position to yield an alkene. </li></ul>
  19. 22. Dehydration in Acid <ul><li>Alcohols undergo dehydration in the presence of a strong acid. </li></ul><ul><li>Acids commonly used for dehydration: </li></ul>p -toluenesulfonic acid TsOH sulfuric acid
  20. 23. Zaitsev Rule <ul><li>The more substituted the alkene is the major product when a mixture of constitutional isomers is possible. </li></ul>
  21. 24. Recall the Mechanism for an E1 Reaction Again, this the kinetically and thermodynamically favored route
  22. 25. Provide the mechanism for the less favored route.
  23. 26. Provide the mechanism for the less favored route.
  24. 27. Also remember, 1° alcohols will react via an E2 mechanism
  25. 28. Unexpected products in an elimination reaction <ul><li>Reason, more stable carbocations are formed from less stable ones by a shift of a hydrogen atom or alkyl group. The shifts are called 1,2-shifts because: </li></ul>If R = -CH 3 then called a methyl shift If H then a hydride shift
  26. 29. Think of the possibilities A 1,2-methyl shift occurs during the dehydration of this compound A 1,2-hydride shift occurs during the dehydration of this compound
  27. 30. Used curved arrows to show the methyl shift when 3,3-dimethyl-2-butanol is treated with sulfuric acid. Used curved arrows to show the hydride shift when 3-methyl-2-butanol is treated with sulfuric acid.
  28. 33. Sometimes it is necessary to use a little more finesse in order to do a dehydration reaction with an alcohol. Reaction conditions
  29. 34. And what I mean by that is… <ul><li>You can execute a dehydration reaction with POCl 3 and pyradine in order to avoid the use of strong acid. </li></ul>
  30. 35. Conversion of alcohols into Alkyl Halides <ul><li>R-OH + H-X  R-X + H 2 O </li></ul><ul><li>Remember </li></ul><ul><li>R-OH + X -  R-X + HO - too poor a leaving group </li></ul>
  31. 36. 1° alcohols will react via an S N 2 mechanism
  32. 37. 2° and 3 ° alcohols will react via an S N 1 mechanism
  33. 38. Cl - is the poorest of the halide nucleophiles, and thus, needs help
  34. 39. Let’s not forget stereochemistry
  35. 41. Predict the product(s)
  36. 43. Conversion of alcohols to alkyl chlorides <ul><li>Example: </li></ul><ul><li>CH 3 -CH 2 -OH + SOCl 2  CH 3 -CH 2 -Cl + SO 2 + Cl - </li></ul>pyradine
  37. 44. Conversion of alcohols to alkyl bromides <ul><li>Example: </li></ul><ul><li>CH 3 -CH 2 -OH + PBr 3  CH 3 -CH 2 -Br + HOPBr 2 </li></ul>
  38. 45. Can be used for all HI ROH  RI Best for CH 3 OH and 1° and 2° alcohols PBr 3 + pyridine ROH  RCBr Can be used for all HBr ROH  RCBr Best for CH 3 OH and 1° and 2° alcohols SOCl 2 + pyridine ROH  RCl Can be used for all HCl ROH  RCl Usefullness reagent reaction
  39. 46. Conversion of alcohols to tosylates <ul><li>Reaction: </li></ul>
  40. 47. Mechanism:
  41. 50. Reaction of Ethers with Strong Acids <ul><li>Example: </li></ul>
  42. 51. Mechanism
  43. 53. Use curved arrows to indicate the mechanism.
  44. 54. Reactions of epoxides <ul><li>Ring opening with strong nucleophiles </li></ul>Which way do we go?
  45. 55. In an unsymmetrical epoxide, the nucleophile attacks at the less substituted carbon atom.
  46. 56. Reactions with acids – HX The nucleophile adds here to the more substituted carbon because it is more able to accept a partial positive charge.

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