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Alkenes, Reactions

Alkenes, Reactions. R-H R-X R-OH R-O-R Alkenes. Acids Bases Metals Oxidation Reduction Halogens. Alkenes, reactions . Addition ionic free radical Reduction Oxidation Substitution. Reactions, alkenes: Addition of hydrogen (reduction).

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Alkenes, Reactions

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  1. Alkenes, Reactions

  2. R-H R-X R-OH R-O-R Alkenes Acids Bases Metals Oxidation Reduction Halogens

  3. Alkenes, reactions. Addition ionic free radical Reduction Oxidation Substitution

  4. Reactions, alkenes: • Addition of hydrogen (reduction). • Addition of halogens. • Addition of hydrogen halides. • Addition of sulfuric acid. • Addition of water (hydration). • Addition of aqueous halogens (halohydrin formation). • Dimerization. • Alkylation.

  5. Oxymercuration-demercuration. • Hydroboration-oxidation. • Addition of free radicals. • Polymerization. • Addition of carbenes. • Epoxidation. • Hydroxylation. • Allylic halogenation • Ozonolysis. • Vigorous oxidation.

  6. Addition of hydrogen (reduction). • | | | | • — C = C — + H2 + Ni, Pt, or Pd  — C — C — • | | • H H • a)Requires catalyst. • #1 synthesis of alkanes • CH3CH=CHCH3 + H2, Ni  CH3CH2CH2CH3 • 2-butene n-butane

  7. Alkanes Nomenclature Syntheses 1. addition of hydrogen to an alkene 2. reduction of an alkyl halide a) hydrolysis of a Grignard reagent b) with an active metal and acid 3. Corey-House Synthesis Reactions 1. halogenation 2. combustion (oxidation) 3. pyrolysis (cracking)

  8. heat of hydrogenation: CH3CH=CH2 + H2, Pt  CH3CH2CH3 + ~ 30 Kcal/mole ethylene 32.8 propylene 30.1 cis-2-butene 28.6 trans-2-butene 27.6 isobutylene 28.4

  9. fats & oils: triglycerides O CH2—O—CCH2CH2CH2CH2CH2CH2CH2CH2CH3 | O CH—O—CCH2CH2CH2CH2CH2CH2CH2CH2CH3 | O CH2—O—CCH2CH2CH2CH2CH2CH2CH3 “saturated” fat

  10. O CH2—O—CCH2CH2CH2CH2CH=CH2CH2CH2CH3 | O CH—O—CCH2CH2CH2CH2CH=CH2CH2CH2CH3 | O CH2—O—CCH2CH2CH=CHCH2CH2CH3 Ω - 3 “unsaturated” oil

  11. Saturated triglycerides are solids at room temperature and are called “fats”. butter fat, lard, vegetable shortening, beef tallow, etc. Unsaturated triglycerides have lower mp’s than saturated triglycerides. Those that are liquids at room temperature are called “oils”. (All double bonds are cis-.) corn oil, peanut oil, Canola oil, cottonseed oil, etc.

  12. polyunsaturated oils + H2, Ni  saturated fats liquid at RT solid at RT oleomargarine butter substitute (dyed yellow) Trans-fatty acids formed in the synthesis of margarine have been implicated in the formation of “bad” cholesterol, hardening of the arteries and heart disease. 

  13. 2) Addition of halogens. • | | | | • — C = C — + X2 — C — C — • | | • X X • X2 = Br2 or Cl2 • test for unsaturation with Br2 • CH3CH2CH=CH2 + Br2/CCl4  CH3CH2CHCH2 • Br Br • 1-butene 1,2-dibromobutane

  14. Addition of hydrogen halides. • | | | | • — C = C — + HX  — C — C — • | | • H X • HX = HI, HBr, HCl • Markovnikov orientation • CH3CH=CH2 + HI  CH3CHCH3 • I • CH3 CH3 • CH2C=CH2 + HBr  CH3CCH3 • Br

  15. Markovnikov’s Rule: In der Hinzufügung einer Säure zu einem alkene wird der Wasserstoff zum Vinylkohlenstoff gehen, der schon den größeren Anzahl Wasserstoffe hat. In the addition of an acid to an alkene the hydrogen will go to the vinyl carbon that already has the greater number of hydrogens.

  16. Regla de Markovnikov: En la adición iónica de un ácido al doble enlace de un alqueno, el hidrógeno de aquél se une al átomo de carbono que ya tiene el mayor número de hidrógenos. “Al que tiene, le será dado.” “El que tiene, recibirá.”

  17. Dans l'addition d'un acide à un alcène l'hydrogène ira au carbone de vinyle qui a déjà le nombre plus grand de hydrogène. 알켄에 산의 추가안에 수소는 이미 수소의 더 중대한 수가 있는 비닐 탄소에는에 갈 것이다. アルケンへの酸の付加で水素はビニールカーボンにへ行く既に水素の大きい数がある。 В дополнении кислоты к алкен водород будет идти в углерод винила, который уже имеет больший номер(число) водорода.

  18. CH3CH2CH=CH2 + HCl CH3CH2CHCH3 Cl CH3 CH3 CH3CH=CCH3 + HBr CH3CH2CCH3 Br CH3CH=CHCH3 + HI  CH3CH2CHCH3 I

  19. An exception to Markovikov’s Rule: CH3CH=CH2 + HBr, peroxides CH3CH2CH2Br CH3 CH3 CH3C=CH2 + HBr, peroxides CH3CHCH2Br “anti-Markovnikov” orientation note: this is only for HBr.

  20. Markovnikov doesn’t always correctly predict the product! CH3 CH3 CH2=CHCHCH3 + HI  CH3CH2CCH3 I Rearrangement!

  21. why Markovinkov? CH3CH=CH2 + HBr  CH3CHCH2 1o carbocation |   H or? CH3CHCH2 2o carbocation  | more stable H + Br- CH3CHCH3 | Br

  22. In ionic electrophilic addition to an alkene, the electrophile always adds to the carbon-carbon double bond so as to form the more stable carbocation.

  23. Addition of sulfuric acid. • | | | | • — C = C — + H2SO4 — C — C — • | | • H OSO3H • alkyl hydrogen sulfate • Markovnikov orientation. • CH3CH=CH2 + H2SO4  CH3CHCH3 • O • O-S-O • OH

  24. Addition of water. • | | | | • — C = C — + H2O, H+ — C — C — • | | • H OH • a) requires acid • Markovnikov orientation • low yield  • CH3CH2CH=CH2 + H2O, H+  CH3CH2CHCH3 • OH

  25. | | H+ | | — C = C — + H2O  — C — C — | | OH H Mechanism for addition of water to an alkene to form an alcohol is the exact reverse of the mechanism (E1) for the dehydration of an alcohol to form an alkene.

  26. How do we know that the mechanism isn’t this way? One step, concerted, no carbocation

  27. CH3CH=CH2 + Br2 + H2O + NaCl  CH3CHCH2 + CH3CHCH2 + CH3CHCH2 Br Br OH Br Cl Br

  28. Some evidence suggests that the intermediate is not a normal carbocation but a “halonium” ion: | | — C — C — Br  The addition of X2 to an alkene is an anti-addition.

  29. Addition of halogens + water (halohydrin formation): • | | | | • — C = C — + X2, H2O  — C — C — + HX • | | • OH X • X2 = Br2, Cl2 • Br2 = electrophile • CH3CH=CH2 + Br2(aq.)  CH3CHCH2 + HBr • OH Br

  30. Dimerization: • CH3 CH3 CH3 • CH3C=CH2 + H2SO4, 80oC  CH3C-CH=CCH3 • CH3 • + • CH3 CH3 • CH3C-CH2C=CH2 • CH3

  31. carbocation as electrophile

  32. Alkylation: • CH3CH3 • CH3C=CH2 + CH3CHCH3 + HF, 0oC  • CH3 CH3 • CH3C-CH2CHCH3 • CH3 • 2,2,4-trimethylpentane • ( “isooctane” ) • Used to increase gasoline yield from petroleum and to improve • fuel performance.

  33. intermolecular hydride (H:-) transfer

  34. Internal combustion engine (four-stroke). Also called an Otto engine.

  35. 1. Intake stroke: air/fuel mixture is drawn into the cylinder.

  36. 2. Compression stroke: air/fuel mixture is compressed.

  37. Ignition of air/fuel mixture by spark at approximately 0o top dead center.

  38. 3. Power stroke: expanding gases push piston down driving crank shaft around.

  39. 4. Exhaust stroke: CO2 + H2O are pushed out of the cylinder.

  40. <http://www.k-wz.de/vmotor/v_omotore.html>

  41. Compression is the key to building a more powerful four-stroke engine. The more the air/fuel mixture is compressed prior to ignition, the more efficient is the conversion of heat energy into mechanical motion. Increasing the compression ratio => • More powerful engine. • Lighter engine (greater power to weight ratio). • Greater fuel economy.

  42. But, compression of the air/fuel mixture above a certain point causes “knocking”.  PV = nRT T  P If, during compression of an air/fuel mixture, the temperature goes high enough, the mixture may explode prematurely.

  43. A knocking sound is produced by an internal combustion engine when fuel ignites spontaneously and prematurely (pre-ignition) during the compression cycle in an engine’s combustion chamber. Consequently, the piston will be forced down when it should be traveling upwards on its compression stroke. At best, knocking reduces the performance of the engine; at worst, it can damage the engine’s moving parts. 

  44. Fuel for four-stroke internal combustion engines: Gasoline ( historically a waste product from the production of kerosene ). Gasoline is a complex mixture of hydrocarbons distilled from petroleum. It is mixed with air to form an explosive mixture. Gasoline + (xs) O2, spark  CO2 + H2O + heat

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