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Alicyclics

Alicyclics Aliphatic compounds containing rings, cycloalkanes, cycloalkyl halides, cycloalkyl alcohols, cyclic ethers, cycloalkenes, cycloalkadienes, etc. Cycloalkanes. cyclopropane cyclobutane cyclopentane cyclohexane . methylcyclopentane 1,1-dimethylcyclobutane.

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Alicyclics

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  1. Alicyclics Aliphatic compounds containing rings, cycloalkanes, cycloalkyl halides, cycloalkyl alcohols, cyclic ethers, cycloalkenes, cycloalkadienes, etc.

  2. Cycloalkanes cyclopropane cyclobutane cyclopentane cyclohexane

  3. methylcyclopentane 1,1-dimethylcyclobutane trans-1,2-dibromocyclohexane

  4. cycloalkenes 3 4 2 5 1 6 cyclopentene 3-methylcyclohexene 1,3-cyclobutadiene

  5. cyclohexanol ethyl cyclopentyl ether cyclohexyl alcohol

  6. Cycloalkanes, syntheses: • Modification of a ring compound: • 1. reduction of cycloalkene • 2. reduction of cyclic halide • a) hydrolysis of Grignard reagent • b) active metal & acid • 3. Corey House • B. Ring closures

  7. A. Modification of a cyclic compound: H2, Ni Sn, HCl Mg; then H2O

  8. Li CuI + CH3CH2-Br CH2CH3 must be 1o Corey-House

  9. ring closures • CH2=CH2 + CH2CO, hv  • Br-CH2CH2CH2CH2CH2-Br + Zn  • etc.

  10. cycloalkanes, reactions: • halogenation • 2. combustion • 3. cracking • 4. exceptions Cl2, heat + HCl

  11. exceptions: H2, Ni, 80o CH3CH2CH3 Cl2, FeCl3 Cl-CH2CH2CH2-Cl H2O, H+ CH3CH2CH2-OH conc. H2SO4 CH3CH2CH2-OSO3H HI CH3CH2CH2-I

  12. exceptions (cont.) + H2, Ni, 200o CH3CH2CH2CH3 ??????????

  13. internal bond deviation heat of angles from 109.5 combustion 60o-49.5o 166.6 90o-19.5o 164.0 108o -1.5o158.7

  14. Cyclopropane undergoes addition reactions that other cycloalkanes and alkanes do not. This is because of angle strain in the small ring. Because the bond angles are less than the optimal 109.5o for maximum overlap, the bonds are weaker than normal carbon-carbon single bonds and can be added to. Cyclobutane has angle strain that is less than that for cyclopropane, reacts with H2/Ni at a higher temperature, but does not react like cylcopropane in the other exceptional reactions.

  15. internal bond deviation heat of angles from 109.5 combustion 60o-49.5o 166.6 90o-19.5o 164.0 108o -1.5o158.7 120o +11.5o157.4 128.5o +19o158.3 135o +25.5o158.6

  16. Cyclohexane does not have any angle strain! It isn’t a flat molecule. By rotating about the carbon-carbon bonds, it can achieve 109.5o bond angles.

  17. conformations of cyclohexane chair twist boat boat

  18. The chair conformation of cyclohexane is free of both angle strain and torsional strain (deviation from staggered). This is the most stable conformation.

  19. The boat conformation is free of angle strain, but has a great deal of torsional strain (eclipsed). To relieve the strain, it twists slightly to form the twist boat:

  20. a = axial positions in the chair conformation e = equatorial positions

  21. CH3 in axial position CH3 in equatorial position is more stable

  22. Cycloalkenes, syntheses: • Modification of a ring compound: • 1) dehydrohalogenation of an alkyl halide • 2) dehydration of an alcohol • 3) dehalogenation of vicinal dihalides • (B. Ring closures)

  23. KOH(alc) H+, Δ cyclohexene Zn

  24. Cycloalkenes, reactions: • addition of H2 8. hydroboration-oxid. • addition of X2 9. addition of free radicals • addition of HX 10. addition of carbenes • addition of H2SO4 11. epoxidation • addition of H2O,H+ 12. hydroxylation • addition of X2 + H2O 13. allylic halogenation • oxymerc-demerc. 14. ozonolysis • 15. vigorous oxidation

  25. H2, Pt Br2, CCl4 trans-1,2-dibromocyclohexane

  26. HBr H2SO4 H2O, H+ Markovnikov orientation

  27. Br2 (aq.) H+, dimer. HF, 0o

  28. HBr, peroxides polymerization CH2CO, hν Peroxybenzoic acid

  29. KMnO4 cis-1,2-cyclohexanediol HCO3H trans-1,2-cyclohexanediol Br2, heat

  30. stereoselective

  31. cyclic alcohols, halides, ethers as expected: PBr3 Na H+ CH3COOH + NaOCl

  32. NaOH 2o alkyl halide => E2 Mg H2O conc. HI, heat conc. HBr, heat 2 Br-CH2CH2-Br 1,4-dioxane

  33. Alicyclic compounds are chemically like their open chain analogs. The exceptions are for small ring compounds where angle strain may give rise to reactions that are not typical of other molecules.

  34. Epoxides: ethylene oxide propylene oxide cyclopentene oxide (oxirane) (methyloxirane) Synthesis: C6H5CO3H cis-2-butene β-butylene oxide

  35. epoxides, reactions: • acid catalyzed addition OH CH2CH2 OH H2O, H+ OH CH3CH2-O-CH2CH2 CH3CH2OH, H+ OH CH2CH2 Br HBr

  36. 2. Base catalyzed addition OH CH2CH2 OH CH3CH2-O-CH2CH2-OH H2N-CH2CH2-OH CH3CH2CH2CH2-OH

  37. mechanism for acid catalyzed addition to an epoxide

  38. mechanism for base-catalyzed addition to an epoxide:

  39. acid catalyzed addition to unsymmetric epoxides? OH + H2O, H+ CH3CHCH2 OH which oxygen in the product came from the water? 18OH CH3CHCH2 OH + H218O, H+

  40. CH3 O + CH3OH,H+ CH3CHCH2 OH Br + HBr  CH3CHCH2 OH

  41. Base? 18OH + Na18OH, H218O CH3CHCH2 OH OCH3 + CH3OH, CH3ONa CH3CHCH2 OH NH2 + NH3 CH3CHCH2 OH

  42. Acid: Z + HZ CH3CHCH2 OH Base: Z + Z-, HZ CH3CHCH2 OH

  43. “variable transition state” Z acid: — C — C — OH ‡ Bond breaking is occurring faster than bond making, making the carbon slightly positive. C δ+ : 3o > 2o > 1o δ+ δ+ base: Z — C — C — O ‡ Bond breaking is occurring at the same time as bond breaking, there is no charge on the carbon. Steric factors are most important: 1o > 2o > 3o δ-

  44. Acid: Z + HZ CH3CHCH2 OH Cδ+: Z to 2o carbon Base: Z + Z-, HZ CH3CHCH2 OH steric factors: Z to 1o carbon

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