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Transcript
CLAS – Chem 109 B - Ch. 10 e-mail: [email protected] website: http://clas.sa.ucsb.edu/staff/terri/ drop-in: T/R 2-3 and F 11-1 (SRB 3274) I. Alcohols ⇒ for this chapter you’ll see alcohols undergoing nucleophilic substitution, elimination and oxidation. 1° alcohol 2° alcohol 3° alcohol benzyl/allyl alcohol HI or HBr SN2 SN1 SN1 SN1 HCl / ZnCl2 SN2 SN1 SN1 SN1 PBr3 or PCl3 / pyridine SN2 SN2 SN1 SOCl2 / pyridine SN2 SN2 SN1 RSO2Cl in pyridine ex TsCl pre - SN2 pre - SN2 pre - E2 H2SO4 / Δ E2 E1 E1 E1 POCl3 / pyridine, cold E2 E2 E2 E2 H2CrO4 or K2Cr2O7 / H2SO4 Oxidation ⇒ carboxylic acid Oxidation ⇒ Ketone N/A 1° ⇒ carboxylic acid 2° ⇒ ketone PCC / CH2Cl2 Oxidation ⇒ Aldehyde Oxidation ⇒ Ketone N/A 1° ⇒ aldehyde 2° ⇒ ketone NaOCl / CH3COOH cold Oxidation ⇒ Aldehyde Oxidation ⇒ Ketone N/A 1° ⇒ aldehyde 2° ⇒ ketone ‘Swern’ 1. Me2SO, C2O2Cl2 cold 2. triethylamine Oxidation ⇒ Aldehyde Oxidation ⇒ Ketone N/A 1° ⇒ aldehyde 2° ⇒ ketone Reagent 1° or 2° ⇒ SN2 3° ⇒ SN1 1° or 2° ⇒ SN2 3° ⇒ SN1 1° or 2° ⇒ pre-SN2 3° ⇒ pre E2 II. Ethers ⇒ In this chapter you will see ethers undergoing nucleophilic substitution reactions with HI or HBr producing an alkyl halide (substituted product) and an alcohol (leaving group) - since the oxygen in the ether is bonded to 2 carbons your primary concern is to determine which one will be substituted – SN1 is preferred over SN2 because the ether is in acidic solution – therefore the order of preference is… benzylic/allylic (SN1) > 3° (SN1) > methyl (SN2) > 1° (SN2) > 2° (SN2) III. Epoxides ⇒ In this chapter you will see epoxides undergoing nucleophilic substitution (only SN2) reactions aka ring opening reactions - epoxides are ethers with lots of ring strain – the strain allows them to react with a large number of nucleophiles unlike typical ethers which only react with HI or HBr – similar to typical ethers your primary concern is to determine which carbon will be substituted – for epoxides the carbon that is substituted depends on if the epoxide is in acidic verses basic conditions Acidic (SN1-ish) ⇒ 3° > 2° > 1° Basic or Neutral (SN2) ⇒ 1° > 2° > 3° IV. Arene Oxides ⇒ In this chapter you will see arene oxides undergoing either nucleophilic substitution reactions same as epoxides in basic/neutral conditions or rearrangement reactions to produce phenol (primary focus) – since there’s a carbocation formed in the rearrangement reaction this will determine which carbon gets the OH – any additional substituents that can stabilize a carbocation (electron donating) will speed up rearrangement V. Amines ⇒ In this chapter you will see amines primarily acting as bases or nucleophiles – since the leaving group of amines are such a strong bases they cannot undergo substitution or elimination reactions VI. Quaternary ammonium hydroxides ⇒ In this chapter you will see quaternary ammonium hydroxides undergoing Hoffmann (aka anti-Zaitsev) elimination reactions (only E2)– there are four carbons bonded to the nitrogen and therefore there can be up to twelve β-carbons to choose from – however in an anti-Zaitsev elimination the order of preference is benzylic/allylic > 1° > 2° > 3° VII. Sulfur functional groups ⇒ In this chapter you will see thiols reacting as a nucleophile to produce sulfides aka thio esters – thio esters can also react as nucleophiles to produce sulfonium ions – sulfonium ions can undergo SN2 reactions Chapter 10 Practice 1. 2. 7. 8. 3. 9. 4. 10. 5. 11. 6. 12. 13. 26. 14. 27. 28. 15. 29. 16. CH3CH2CH2CH2CH2CH2OH 17. 18. 19. 30. 31. 32. 20. 33. 21. 34. 22. 35. 23. 36. 1. RCO3H 24. 2. HO-, H2O 37. 25. 1. OsO4 2. H2O2, H2O 38. 41. 39. 42. 40. 43. H3C N H CH3 44. Rank the following alcohols in order of increasing rate of dehydration in the presence of sulfuric acid. 45. Which primary amine will form the following product when undergoing 2 successive Hoffman degradations? 46. Indicate how the following compound could be synthesized using the given starting material and any necessary reagents. 47. What is the major product of rearrangement for the following arene oxide? 48. What is the major product of rearrangement for the following arene oxides? Which arene oxide is more likely to be carcinogenic? 49. Explain why elimination of 2-bromopentane produces 2-pentene whereas elimination of the quaternary ammonium ion produces 1-pentene. OH