Alkenes, Reactions

NR      some NR        Acids Bases Metals Oxidation Reduction Halogens R-H R-X R-OH R-O-R Alkenes

Alkenes, reactions. Addition ionic free radical Reduction Oxidation Substitution

Reactions, alkenes: 1.Addition of hydrogen (reduction). 2.Addition of halogens. 3.Addition of hydrogen halides. 4.Addition of sulfuric acid. 5.Addition of water (hydration). 6.Addition of aqueous halogens (halohydrin formation). 7.Dimerization. 8.Alkylation.

9.Oxymercuration-demercuration. 10.Hydroboration-oxidation. 11.Addition of free radicals. 12.Polymerization. 13.Addition of carbenes. 14.Epoxidation. 15.Hydroxylation. 16.Allylic halogenation 17.Ozonolysis. 18.Vigorous oxidation.

1.Addition of hydrogen (reduction). | | | | — C = C — + H 2 + Ni, Pt, or Pd  — C — C — | | H H a) Requires catalyst. b)#1 synthesis of alkanes CH 3 CH=CHCH 3 + H 2, Ni  CH 3 CH 2 CH 2 CH 3 2-butene n-butane

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)

heat of hydrogenation: CH 3 CH=CH 2 + H 2, Pt  CH 3 CH 2 CH 3 + ~ 30 Kcal/mole ethylene32.8 propylene30.1 cis-2-butene28.6 trans-2-butene27.6 isobutylene28.4

fats & oils: triglycerides O CH 2 —O—CCH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 | O CH—O—CCH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 | O CH 2 —O—CCH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 “saturated” fat

O CH 2 —O—CCH 2 CH 2 CH 2 CH 2 CH=CH 2 CH 2 CH 2 CH 3 | O CH—O—CCH 2 CH 2 CH 2 CH 2 CH=CH 2 CH 2 CH 2 CH 3 | O CH 2 —O—CCH 2 CH 2 CH=CHCH 2 CH 2 CH 3 Ω - 3 “unsaturated” oil

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.

polyunsaturated oils + H 2, 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. 

2) Addition of halogens. | | | | — C = C — + X 2  — C — C — | | X X a)X 2 = Br 2 or Cl 2 b)test for unsaturation with Br 2 CH 3 CH 2 CH=CH 2 + Br 2 /CCl 4  CH 3 CH 2 CHCH 2 Br Br 1-butene 1,2-dibromobutane

3.Addition of hydrogen halides. | | | | — C = C — + HX  — C — C — | | H X a)HX = HI, HBr, HCl b)Markovnikov orientation CH 3 CH=CH 2 + HI  CH 3 CHCH 3 I CH 3 CH 3 CH 2 C=CH 2 + HBr  CH 3 CCH 3 Br

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.

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.”

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.

CH 3 CH 2 CH=CH 2 + HCl  CH 3 CH 2 CHCH 3 Cl CH 3 CH 3 CH 3 CH=CCH 3 + HBr  CH 3 CH 2 CCH 3 Br CH 3 CH=CHCH 3 + HI  CH 3 CH 2 CHCH 3 I

An exception to Markovikov’s Rule: CH 3 CH=CH 2 + HBr, peroxides  CH 3 CH 2 CH 2 Br CH 3 CH 3 CH 3 C=CH 2 + HBr, peroxides  CH 3 CHCH 2 Br “anti-Markovnikov” orientation note: this is only for HBr.

Markovnikov doesn’t always correctly predict the product! CH 3 CH 3 CH 2 =CHCHCH 3 + HI  CH 3 CH 2 CCH 3  I Rearrangement!

why Markovinkov? CH 3 CH=CH 2 + HBr  CH 3 CHCH 2 1 o carbocation |   H or? CH 3 CHCH 2 2 o carbocation  | more stable H + Br -  CH 3 CHCH 3 | Br

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.

4.Addition of sulfuric acid. | | | | — C = C — + H 2 SO 4  — C — C — | | H OSO 3 H alkyl hydrogen sulfate Markovnikov orientation. CH 3 CH=CH 2 + H 2 SO 4  CH 3 CHCH 3 O O-S-O OH

5.Addition of water. | | | | — C = C — + H 2 O, H +  — C — C — | | H OH a) requires acid b)Markovnikov orientation c)low yield  CH 3 CH 2 CH=CH 2 + H 2 O, H +  CH 3 CH 2 CHCH 3 OH

| | H + | | — C = C — + H 2 O  — 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.

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

CH 3 CH=CH 2 + Br 2 + H 2 O + NaCl  CH 3 CHCH 2 + CH 3 CHCH 2 + CH 3 CHCH 2 Br Br OH Br Cl Br

Some evidence suggests that the intermediate is not a normal carbocation but a “halonium” ion: | | — C — C — Br  The addition of X 2 to an alkene is an anti-addition.

6.Addition of halogens + water (halohydrin formation): | | | | — C = C — + X 2, H 2 O  — C — C — + HX | | OH X a)X 2 = Br 2, Cl 2 b)Br 2 = electrophile CH 3 CH=CH 2 + Br 2 (aq.)  CH 3 CHCH 2 + HBr OH Br

7.Dimerization: CH 3 CH 3 CH 3 CH 3 C=CH 2 + H 2 SO 4, 80 o C  CH 3 C-CH=CCH 3 CH 3 + CH 3 CH 3 CH 3 C-CH 2 C=CH 2 CH 3

carbocation as electrophile

8.Alkylation: CH 3 CH 3 CH 3 C=CH 2 + CH 3 CHCH 3 + HF, 0 o C  CH 3 CH 3 CH 3 C-CH 2 CHCH 3 CH 3 2,2,4-trimethylpentane ( “isooctane” ) Used to increase gasoline yield from petroleum and to improve fuel performance.

intermolecular hydride (H: - ) transfer

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

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

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

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

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

4. Exhaust stroke: CO 2 + H 2 O are pushed out of the cylinder.

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 => 1.More powerful engine. 2.Lighter engine (greater power to weight ratio). 3.Greater fuel economy.

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.

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. 

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) O 2, spark  CO 2 + H 2 O + heat

The fuel limits how high the compression ratio can be before the engine knocks. CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 knocks like crazy at n-heptanelow compression. CH 3 CH 3 CH 3 CCH 2 CHCH 3 resists knocking CH 3 2,2,4-trimethylpentane ( “isooctane” )

Octane rating: a measure of the resistance of a fuel to knock in an internal combustion engine at high compression ratios. Determined by comparing the fuel to mixtures of: n-heptane (octane number = 0) and 2,2,4-trimethylpentane (octane number = 100) in a test engine.

Tetraethyl lead, (CH 3 CH 2 ) 4 Pb, was discovered to increase the octane rating of gasoline. Lead is extremely toxic, especially in small children where exposure leads to nerve damage. All gasoline in the US is now “lead free”. Tetraethyl lead has been replaced by “alkylates” and catalytically reformed hydrocarbons.

Compression vs. Octane Number 5:1 72 6:1 81 7:1 87 8:1 92 9: : : :1 108

Use the octane rating recommended by your car maker! Using a higher octane gasoline only puts more of your money into the fuel company’s pockets.

9.Oxymercuration-demercuration. | | | | — C = C — + H 2 O, Hg(OAc) 2  — C — C — + acetic | | acid OH HgOAc | | | | — C — C — + NaBH 4  — C — C — | | | | OH HgOAc OH H alcohol

oxymercuration-demercuration: a)#1 synthesis of alcohols. b)Markovnikov orientation. c)100% yields. d)no rearrangements CH 3 CH 2 CH=CH 2 + H 2 O, Hg(OAc) 2 ; then NaBH 4  CH 3 CH 2 CHCH 3 OH

With alcohol instead of water: alkoxymercuration-demercuration: | | | | — C =C — + ROH, Hg(TFA) 2  — C — C — | | OR HgTFA | | | | — C — C — + NaBH 4  — C — C — | | | | OR HgTFA OR H ether

alkoxymercuration-demercuration: a)#2 synthesis of ethers. b)Markovnikov orientation. c)100% yields. d)no rearrangements CH 3 CH=CH 2 + CH 3 CHCH 3, Hg(TFA) 2 ; then NaBH 4  OH CH 3 CH 3 CH 3 CH-O-CHCH 3 diisopropyl ether Avoids the elimination with 2 o /3 o RX in Williamson Synthesis.

Ethers nomenclature syntheses 1. Williamson Synthesis 2. alkoxymercuration-demercuration reactions 1. acid cleavage

10.Hydroboration-oxidation. | | — C = C — + (BH 3 ) 2  — C — C — | | diborane H B — | | | | | — C — C — + H 2 O 2, NaOH  — C — C — | | | | H B — H OH | alcohol

hydroboration-oxidation: a)#2 synthesis of alcohols. b)Anti-Markovnikov orientation.  c)100% yields. d)no rearrangements CH 3 CH 2 CH=CH 2 + (BH 3 ) 2 ; then H 2 O 2, NaOH  CH 3 CH 2 CH 2 CH 2 -OH

CH 3 CH 3 C=CH 2 + H 2 O, Hg(OAc) 2 ; then NaBH 4  CH 3 Markovnikov CH 3 CCH 3 OH CH 3 CH 3 C=CH 2 + (BH 3 ) 2 ; then H 2 O 2, NaOH  CH 3 anti-Markovnikov CH 3 CHCH 2 OH

Alcohols: nomenclature syntheses 1. oxymercuration-demercuration 2. hydroboration-oxidation hydrolysis of a 1 o / CH 3 alcohol

11.Addition of free radicals. | | | | — C = C — + HBr, peroxides  — C — C — | | H X a)anti-Markovnikov orientation. b)free radical addition CH 3 CH=CH 2 + HBr, peroxides  CH 3 CH 2 CH 2 -Br

Mechanism for free radical addition of HBr: Initiating steps: 1) peroxide  2 radical 2) radical + HBr  radical:H + Br (Br electrophile) Propagating steps: 3) Br + CH 3 CH=CH 2  CH 3 CHCH 2 -Br (2 o free radical) 4) CH 3 CHCH 2 -Br + HBr  CH 3 CH 2 CH 2 -Br + Br 3), 4), 3), 4)… Terminating steps: 5)Br + Br  Br 2 Etc.

In a free radical addition to an alkene, the electrophilic free radical adds to the vinyl carbon with the greater number of hydrogens to form the more stable free radical. In the case of HBr/peroxides, the electrophile is the bromine free radical (Br). CH 3 CH=CH 2 + HBr, peroxides  CH 3 CH 2 CH 2 -Br

12.Polymerization. CH 2 =CH 2 + heat, pressure  -(CH 2 CH 2 )- n n = 10,000+ polyethylene CH 3 CH=CH 2 polymerization  -(CH 2 CH)- n CH 3 polypropylene CH 2 =CHCl poly…  -(CH 2 CH)- n Cl polyvinyl chloride (PVC)

Plastics: man-made polymers that at some time in their manufacture are soft and pliable. Thermoplastics: plastics that soften when heated. Free radical polymerization. | | | | | | R + — C = C —  R — C — C + — C = C —  | |

13.Addition of carbenes. | | | | — C = C — + CH 2 CO or CH 2 N 2, hν  — C — C —  CH 2 CH 2 “carbene” adds across the double bond | | — C = C —  CH 2

| | | | — C = C — + CHCl 3, t-BuOK  — C— C — CCl 2  -HCl CCl 2 dichlorocarbene | | — C = C —  CCl 2

14. Epoxidation. | | C 6 H 5 CO 3 H | | — C = C — + (peroxybenzoic acid)  — C— C — O epoxide Free radical addition of oxygen diradical. | | — C = C —  O

15. Hydroxylation. (mild oxidation) | | | | — C = C — + KMnO 4  — C — C — syn | | OH OH OH | | | | — C = C — + HCO 3 H  — C — C — anti peroxyformic acid | | OH glycol

CH 3 CH=CHCH 3 + KMnO 4  CH 3 CH-CHCH 3 OH OH 2,3-butanediol test for unsaturation purple KMnO 4  brown MnO 2 CH 2 =CH 2 + KMnO 4  CH 2 CH 2 OH OH ethylene glycol “anti-freeze”

16.Allylic halogenation. | | | | | | — C = C — C — + X 2, heat  — C = C — C — + HX | | H  allyl X CH 2 =CHCH 3 + Br 2, 350 o C  CH 2 =CHCH 2 Br + HBr a) X 2 = Cl 2 or Br 2 b) or N-bromosuccinimide (NBS)

CH 2 =CHCH 3 + Br 2  CH 2 CHCH 3 Br Br addition CH 2 =CHCH 3 + Br 2, heat  CH 2 =CHCH 2 -Br + HBr allylic substitution

17.Ozonolysis. | | | | — C = C — + O 3 ; then Zn, H 2 O  — C = O + O = C — used for identification of alkenes CH 3 CH 3 CH 2 CH=CCH 3 + O 3 ; then Zn, H 2 O  CH 3 CH 3 CH 2 CH=O + O=CCH 3

18.Vigorous oxidation. =CH 2 + KMnO 4, heat  CO 2 =CHR + KMnO 4, heat  RCOOH carboxylic acid =CR 2 + KMnO 4, heat  O=CR 2 ketone

CH 3 CH 2 CH 2 CH=CH 2 + KMnO 4, heat  CH 3 CH 2 CH 2 COOH + CO 2 CH 3 CH 3 CH 3 C=CHCH 3 + KMnO 4, heat  CH 3 C=O + HOOCCH 3

CH 3 CH=CHCH 3 + KMnO 4  CH 3 CHCHCH 3 OHOH mild oxidation  glycol CH 3 CH=CHCH 3 + hot KMnO 4  2 CH 3 COOH vigorous oxidation

Reactions, alkenes: 1.Addition of hydrogen 2.Addition of halogens 3.Addition of hydrogen halides 4.Addition of sulfuric acid 5.Addition of water/acid 6.Addition of halogens & water (halohydrin formation) 7.Dimerization 8.Alkylation

9.Oxymercuration-demercuration 10.Hydroboration-oxidation 11.Addition of free radicals 12.Polymerization 13.Addition of carbenes 14.Epoxidation 15.Hydroxylation 16.Allylic halogenation 17.Ozonolysis 18.Vigorous oxidation

CH 3 CH 3 CH 3 C=CH 2 + H 2, Pt  CH 3 CHCH 3 isobutylene CH 3 “ + Br 2 /CCl 4  CH 3 C-CH 2 Br Br CH 3 “ + HBr  CH 3 CCH 3 Br CH 3 “ + H 2 SO 4  CH 3 CCH 3 O SO 3 H

CH 3 CH 3 CH 3 C=CH 2 + H 2 O, H +  CH 3 CCH 3 isobutylene OH CH 3 “ + Br 2 (aq.)  CH 3 C-CH 2 Br OH CH 3 CH 3 CH 3 CH 3 C=CH 2 + H 2 SO 4, 80 o C  CH 3 C-CH=CCH 3 (dimeriz.) CH 3 CH 3 CH 3 + CH 3 C-CH 2 C=CH 2 CH 3

CH 3 CH 3 CH 3 C=CH 2 + CH 3 CHCH 3 + HF, 0 o C  CH 3 CH 3 CH 3 C-CH 2 CHCH 3 CH 3 CH 3 CH 3 CH 3 C=CH 2 + H 2 O,Hg(OAc) 2 ; then NaBH 4  CH 3 CCH 3 OH CH 3 “ + (BH 3 ) 2 ; then H 2 O 2, OH -  CH 3 CHCH 2 OH

CH 3 CH 3 CH 3 C=CH 2 + HBr, peroxides  CH 3 CHCH 2 isobutylene Br CH 3 “ + polym.  -(CH 2 C)- n CH 3 “ + CH 2 CO, hv  CH 3 C–CH 2 CH 2 CH 3 “ + PBA  CH 3 C–CH 2 O

CH 3 CH 3 CH 3 C=CH 2 + KMnO 4  CH 3 C–CH 2 isobutylene OH OH CH 3 “ + Br 2, heat  CH 2 C=CH 2 + HBr Br CH 3 “ + O 3 ; then Zn/H 2 O  CH 3 C=O + O=CH 2 CH 3 “ + KMnO 4, heat  CH 3 C=O + CO 2