Hoá học hữu cơ - Chương 7: Hydrocarbon chưa no mạch hơ

HOAHOÁÙ HOHỌÏCC HHƯỮŨU CƠCƠ OrganicOrganic ChemistryChemistry CHƯƠNG 7 HYDROCARBON CHƯA NO MẠCH HỞ GIỚI THIỆU CHƯƠNG 7.1. ALKENES 7.2. ALKADIENES 7.3. ALKYNES 7.1. ALKENES 7.1.1. DANH PHÁP & ĐỒNG PHÂN 7.1.2. CÁC PHƯƠNG PHÁP ĐIỀU CHẾ 7.1.3. TÍNH CHẤT 7.1.4. Ứng dụng IntroductionIntroduction ►► RelativeRelative StabilitiesStabilities ofof AlkenesAlkenes ƒƒ GenerallyGenerally ciscis alkenesalkenes areare lessless stablestable thanthan transtrans alkenesalkenes becausebecause ofof stericsteric hinderancehinderance ƒƒ CisCis alkenesalkenes areare moremore reactivereactive thanthan transtrans alkenesalkenes (hydrogenation(hydrogenation reaction)reaction) IntroductionIntroduction ►► RelativeRelative StabilitiesStabilities ofof AlkenesAlkenes ƒƒ TheThe moremore highlyhighly substitutedsubstituted doubledouble bond,bond, thethe greatergreater thethe alkenealkene’’ss stabilitystability TetrasubstitutedTetrasubstituted >> trisubstitutedtrisubstituted >> disubsituteddisubsituted >> monosubstitutedmonosubstituted ƒƒ WithinWithin thethe disubstituteddisubstituted series:series: 1,11,1 disubstituteddisubstituted >> transtrans >> ciscis >> IUPACIUPAC NomenclatureNomenclature ►►ParentParent isis longestlongest chainchain containingcontaining thethe doubledouble bond.bond. ►►--aneane changeschanges toto --eneene.. (or(or --dienediene,, --trienetriene)) ►►NumberNumber thethe chainchain soso thatthat thethe doubledouble bondbond hashas thethe lowestlowest possiblepossible number.number. ►►InIn aa ring,ring, thethe doubledouble bondbond isis assumedassumed toto bebe betweenbetween carboncarbon 11 andand carboncarbon 2.2. =>=> AlkeneAlkene SubstituentsSubstituents = CH2 -CH = CH2 -CH2 -CH = CH2 methylene vinyl allyl (methylidene) (ethenyl) (2-propenyl) Name: => CisCis--transtrans IsomerismIsomerism ►►SimilarSimilar groupsgroups onon samesame sideside ofof doubledouble bond,bond, alkenealkene isis cis.cis. ►►SimilarSimilar groupsgroups onon oppositeopposite sidessides ofof doubledouble bond,bond, alkenealkene isis trans.trans. ►►CycloalkenesCycloalkenes areare assumedassumed toto bebe cis.cis. ►►TransTrans cycloalkenescycloalkenes areare notnot stablestable unlessunless thethe ringring hashas atat leastleast 88 carbons.carbons. =>=> NameName these:these: H CH3 Br Br CC CC CH3CH2 H H H trans-2-pentene cis-1,2-dibromoethene => ). ). ). ). rules to rules to entgegen entgegen zusammen zusammen Prelog Prelog (for (for - - (for (for E E Z Z Ingold Ingold - - Nomenclature Nomenclature Z Z - - Cahn Cahn E E => Use the If high priority groups are on the same side, the name is If high priority groups are on opposite sides, the name is assign priorities to groups attached each carbon in the double bond. Use the If high priority groups are on the same side, the name is If high priority groups are on opposite => sides, the name is assign priorities to groups attached each carbon in the double bond. ► ► ► ► ► ► Example,Example, EE--ZZ 1 1 2 Cl H C H 1 3 Cl CH CH3 CC CC H CH2 H 2 2 1 2 2Z 5E (2Z, 5E)-3,7-dichloro-2,5-octadiene => StabilityStability ofof AlkenesAlkenes ►►MeasuredMeasured byby heatheat ofof hydrogenation:hydrogenation: AlkeneAlkene ++ HH22 →→ AlkaneAlkane ++ energyenergy ►►MoreMore heatheat released,released, higherhigher energyenergy alkene.alkene. 30.3 kcal 27.6 kcal => SubstituentSubstituent EffectsEffects ►►MoreMore substitutedsubstituted alkenesalkenes areare moremore stable.stable. HH22C=CHC=CH22 << RR--CH=CHCH=CH22 << RR--CH=CHCH=CH--RR << RR--CH=CRCH=CR22 << RR22C=CRC=CR22 unsubunsub.. << monosubmonosub.. << disubdisub.. << trisubtrisub.. << tetratetra sub.sub. ►►AlkylAlkyl groupgroup stabilizesstabilizes thethe doubledouble bond.bond. ►►AlkeneAlkene lessless stericallysterically hindered.hindered. => DisubstitutedDisubstituted IsomersIsomers ►►Stability:Stability: ciscis << geminalgeminal << transtrans isomerisomer ►►LessLess stablestable isomerisomer isis higherhigher inin energy,energy, hashas aa moremore exothermicexothermic heatheat ofof hydrogenation.hydrogenation. CisCis--22--butenebutene CH3 CH3 28.628.6 kcalkcal CC HH IsobutyleneIsobutylene (CH(CH33))22C=CHC=CH22 28.028.0 kcalkcal TransTrans--22--butenebutene H CH3 27.627.6 kcalkcal CC CH3 H => AlkenesAlkenes andand CycloalkenesCycloalkenes 1.1. LocateLocate thethe longestlongest chainchain containingcontaining thethe doubledouble bondbond 2.2. ChangeChange thethe namename ofof thethe correspondingcorresponding parentparent alkanealkane fromfrom --aneane toto --eneene 3.3. TheThe compoundcompound isis numberednumbered toto givegive oneone ofof thethe alkenealkene carbonscarbons thethe lowestlowest numbernumber 4.4. NumberNumber thethe doubledouble bondbond byby thethe numbernumber ofof thethe firstfirst atomatom inin thethe doubledouble bondbond 5.5. NameName substituentssubstituents asas withwith alkanesalkanes 6.6. TheThe doubledouble bondbond ofof aa cycloalkenecycloalkene mustmust bebe inin positionposition 11 andand 22 AlkenesAlkenes andand CycloalkenesCycloalkenes 1-butene 2-hexene 1-methylcyclopentene 3,5-dimethylcyclohexene AlkeneAlkene SynthesisSynthesis OverviewOverview ►►E2E2 dehydrohalogenationdehydrohalogenation ((--HX)HX) ►►E1E1 dehydrohalogenationdehydrohalogenation ((--HX)HX) ►►DehalogenationDehalogenation ofof vicinalvicinal dibromidesdibromides ((--XX22)) ►►DehydrationDehydration ofof alcoholsalcohols ((--HH22O)O) =>=> RemovingRemoving HXHX viavia E2E2 ►►StrongStrong basebase abstractsabstracts HH++ asas XX-- leavesleaves fromfrom thethe adjacentadjacent carbon.carbon. ►►TertiaryTertiary andand hinderedhindered secondarysecondary alkylalkyl halideshalides givegive goodgood yields.yields. ►►UseUse aa bulkybulky basebase ifif thethe alkylalkyl halidehalide usuallyusually formsforms substitutionsubstitution products.products. =>=> SomeSome BulkyBulky BasesBases CH(CH ) CH3 _ 3 2 N CH(CH ) H3C C O 3 2 H NCH3 CH3 H3C tert-butoxide diisopropylamine 2,6-dimethylpyridine (CH3CH2)3N : triethylamine => HofmannHofmann ProductProduct ►► BulkyBulky basesbases abstractabstract thethe leastleast hinderedhindered HH++ ►► LeastLeast substitutedsubstituted alkenealkene isis majormajor product.product. H CH3 _ H3C CH3 CH3CH2 H CH3CH2O CC CC CH3 C C CH2 CH CH OH CH3 H C H H Br H 3 2 H 3 71% 29% H CH3 _ H C CH CH CH H (CH ) CO 3 3 3 2 3 3 CC CC CH3 C C CH2 => CH CH OH CH3 H C H H Br H 3 2 H 3 28% 72% PreparationPreparation ►► DehydrohalogenationDehydrohalogenation H B H B X X DehydrohalogenationDehydrohalogenation:: AnAn E2E2 ReactionReaction ►► BaseBase removeremove aa protonproton onon thethe ββ--carboncarbon ►► TS:TS: developingdeveloping doubledouble bond,bond, leavingleaving XX H BB HH BB HBHB XX XX XX ƒƒ concertedconcerted removalremoval ofof thethe proton,proton, formationformation ofof thethe doubledouble bond,bond, andand departuredeparture ofof thethe leavingleaving groupgroup ƒƒ BothBoth alkylalkyl halidehalide andand basebase coconcentrationsncentrations affectaffect raterate andand thereforetherefore thethe reactionreaction isis 2nd2nd orderorder E2:E2: DiastereomersDiastereomers Ph H H Br CH3 Br H H H Ph ≡ HCH3 Ph Ph CH3 PhPh Br Ph H => Ph CH3 StereospecificStereospecific reaction:reaction: ((SS,, RR)) producesproduces onlyonly transtrans product,product, ((RR,, RR)) producesproduces onlyonly ciscis.. E2:E2: CyclohexanesCyclohexanes LeavingLeaving groupsgroups mustmust bebe transtrans diaxialdiaxial.. =>=> E2:E2: VicinalVicinal DibromidesDibromides ►►RemoveRemove BrBr22 fromfrom adjacentadjacent carbons.carbons. ►►BrominesBromines mustmust bebe antianti--coplanarcoplanar (E2).(E2). ►►UseUse NaINaI inin acetone,acetone, oror ZnZn inin aceticacetic acid.acid. I- Br H CH3 H CH3 CC H3C H => CH H 3 Br RemovingRemoving HXHX viavia E1E1 ►►SecondarySecondary oror tertiarytertiary halideshalides ►►FormationFormation ofof carbocationcarbocation intermediateintermediate ►►WeakWeak nucleophilenucleophile ►►UsuallyUsually havehave substitutionsubstitution productsproducts tootoo =>=> DehydrationDehydration reactionreaction ►► ReactionReaction H H2SO4 H2O OH heat ►► EliminationElimination isis favoredfavored overover substitutionsubstitution atat higherhigher temperaturestemperatures ►► PrimaryPrimary alcoholsalcohols areare mostmost difficultdifficult toto dehydrate,dehydrate, tertiarytertiary areare thethe easiesteasiest ►► RearrangementsRearrangements ofof thethe carboncarbon skeletonskeleton cancan occuroccur DehydrationDehydration ofof AlcoholsAlcohols ►►ReversibleReversible reactionreaction ►►UseUse concentratedconcentrated sulfuricsulfuric oror phosphoricphosphoric acid,acid, removeremove lowlow--boilingboiling alkenealkene asas itit forms.forms. ►►ProtonationProtonation ofof OHOH convertsconverts itit toto aa goodgood leavingleaving group,group, HOHHOH ►►CarbocationCarbocation intermediate,intermediate, likelike E1E1 ►►ProticProtic solventsolvent removesremoves adjacentadjacent HH++ =>=> DehydrationDehydration reactionreaction ►► MechanismMechanism H H2O OH StepStep 1 1 H H H+H+ H H H + + OO OO HH ++ H H HH Step 2 H B + DehydrationDehydration MechanismMechanism H H OH O H OH _ C C OH S OH C C HSO4 O H H OH H H2O: C C + C C CC H3O => IndustrialIndustrial MethodsMethods ►►CatalyticCatalytic crackingcracking ofof petroleumpetroleum ƒƒ LongLong--chainchain alkanealkane isis heatedheated withwith aa catalystcatalyst toto produceproduce anan alkenealkene andand shortershorter alkane.alkane. ƒƒ ComplexComplex mixturesmixtures areare produced.produced. ►►DehydrogenationDehydrogenation ofof alkanesalkanes ƒƒ HydrogenHydrogen (H(H22)) isis removedremoved withwith heat,heat, catalyst.catalyst. ƒƒ ReactionReaction isis endothermic,endothermic, butbut entropyentropy--favored.favored. ►►NeitherNeither methodmethod isis suitablesuitable forfor lablab synthesissynthesis =>=> PhysicalPhysical PropertiesProperties ►► LowLow boilingboiling points,points, increasingincreasing withwith mass.mass. ►► BranchedBranched alkenesalkenes havehave lowerlower boilingboiling points.points. ►► LessLess densedense thanthan water.water. ►► SlightlySlightly polarpolar ƒƒ PiPi bondbond isis polarizable,polarizable, soso instantaneousinstantaneous dipoledipole-- dipoledipole interactionsinteractions occur.occur. ƒƒ AlkylAlkyl groupsgroups areare electronelectron--donatingdonating towardtoward thethe pipi bond,bond, soso maymay havehave aa smallsmall dipoledipole moment.moment. =>=> PolarityPolarity ExamplesExamples H3C CH3 H CH3 CC CC H H H3C H cis-2-butene, bp 4°C trans-2-butene, bp 1°C μ = 0.33 D μ = 0 => ChemistryChemistry ofof AlkenesAlkenes AdditionAddition ReactionReaction BondBond LengthsLengths andand AnglesAngles ►►HybridHybrid orbitalsorbitals havehave moremore ss character.character. ►►PiPi overlapoverlap bringsbrings carboncarbon atomsatoms closer.closer. ►►BondBond angleangle withwith pipi orbitalsorbitals increases.increases. ƒƒ AngleAngle C=CC=C--HH isis 121.7121.7°° ƒƒ AngleAngle HH--CC--HH isis 116.116. 66°° =>=> PiPi BondBond ►►SidewaysSideways overlapoverlap ofof parallelparallel pp orbitals.orbitals. ►►NoNo rotationrotation isis possiblepossible withoutwithout breakingbreaking thethe pipi bondbond (63(63 kcal/mole).kcal/mole). ►►CisCis isomerisomer cannotcannot becomebecome transtrans withoutwithout aa chemicalchemical reactionreaction occurring.occurring. => TypicalTypical AlkeneAlkene ReactionsReactions TheThe carboncarbon--carboncarbon doubledouble bondbond meansmeans thethe presencepresence ofof extraextra electrons.electrons. ReactionsReactions thatthat areare associatedassociated withwith anan electronelectron--richrich situationsituation include:include: 1)1) AdditionAddition ofof protonsprotons (H(H++)) 2)2) OxidationOxidation——thethe lossloss ofof electronselectrons ReductionReduction ofof AlkenesAlkenes ►► HydrogenationHydrogenation reactionreaction ƒƒ HeterogeneousHeterogeneous catalysts:catalysts: finelyfinely divideddivided insolubleinsoluble platinum,platinum, palladiumpalladium oror nickelnickel catalystscatalysts ƒƒ SynSyn additionaddition Me H Me H H2, Pt H H H Me (or Pd, Ni) H Me HydrogenationHydrogenation ofof AlkenesAlkenes catalyst CC + HH C C H H fine powder, very porous, suspended a syn addition in solution reaction The catalyst is Pt, PtO2, Pd, or Ni (in special cases Ru, Rh, Re) ReductionReduction ofof AlkenesAlkenes ►►HydrogenationHydrogenation reactionreaction ƒƒ HeterogeneousHeterogeneous catalystscatalysts Me H2, Pt Me Et Et Et Me Et Me HH (or Pd, Ni) H H RR HH Me H H Et H2, Pt Et Me Me Et (or Pd, Ni) Et Me E SS ReductionReduction ofof AlkenesAlkenes ►► HydrogenationHydrogenation reactionreaction ƒƒ HomogeneousHomogeneous catalysts:catalysts: catalystcatalyst (typically(typically rhodiumrhodium oror rutheniumruthenium based)based) isis solublesoluble inin thethe reactionreaction mediummedium ƒƒ WilkinsonWilkinson’’ss catalystcatalyst isis Rh[(CRh[(C66HH55))33P]P]33ClCl AdditionAddition toto AlkenesAlkenes ►► ReactionReaction exothermicexothermic ƒƒ oneone ππ andand oneone σσ bondbond areare convertedconverted toto twotwo σσ bondsbonds A B A-B ►► TheThe ππ electronselectrons ofof thethe doubledouble bondbond areare looselyloosely heldheld ƒƒ sourcesource ofof electronelectron density,density, ((nucleophilicnucleophilic)) A B A + A-B AdditionAddition toto AlkenesAlkenes ►► AdditionAddition ofof HX,HX, mechanismmechanism H + H-X X- H X MarkovnikovMarkovnikov’’ss RuleRule ►► AdditionAddition ofof HXHX toto anan alkenealkene proceedsproceeds soso thatthat thethe hydrogenhydrogen atomatom addsadds toto thethe carboncarbon thatthat alreadyalready hashas thethe mostmost hydrogenhydrogen atomsatoms H H X H-X H H + H X- MarkovnikovMarkovnikov’’ss RuleRule ►► InIn thethe ionicionic additionaddition ofof anan unsymmetricalunsymmetrical reagentreagent (i.e.,(i.e., HH--X)X) toto aa doubledouble bond,bond, thethe positivepositive portionportion ofof thethe addingadding reagentreagent (i.e.,(i.e., H+)H+) attachesattaches itselfitself toto aa carboncarbon atomatom ofof thethe doubledouble bondbond soso asas toto yieldyield thethe moremore stablestable carbocationcarbocation asas anan intermediateintermediate ►► RegioselectiveRegioselective Reaction:Reaction: AA reactionreaction thatthat cancan potentiallypotentially yieldyield twotwo oror moremore constitutionalconstitutional isomersisomers butbut producesproduces onlyonly oneone oror aa predominancepredominance ofof oneone isomerisomer MarkovnikovMarkovnikov’’ss RuleRule ►► HighlyHighly endergonicendergonic firstfirst stepstep (rate(rate determining)determining) andand aa highlyhighly exergonicexergonic secondsecond stepstep X H H H H δ+ δ+ δ- X H H H H-X + X- H H X MarkovnikovMarkovnikov’’ss RuleRule ►► TheThe productproduct withwith thethe moremore stablestable carbocationcarbocation intermediateintermediate favoredfavored ƒƒ TheThe mostmost stablestable carbocationcarbocation hashas aa lowerlower ΔΔGG‡‡ ƒƒ CarbocationCarbocation--likelike transitiontransition statestate stabilizedstabilized + H H X- H + X- H X H H-X H H X H MarkovnikovMarkovnikov’’ss rulerule ►►WhenWhen anan unsymmetricalunsymmetrical reagentreagent addsadds toto anan unsymmetricunsymmetric alkenealkene,, thethe electropositiveelectropositive partpart ofof thethe reagentreagent bondsbonds toto thethe carboncarbon ofof thethe doubledouble bondbond thatthat hashas thethe greatergreater numbernumber ofof hydrogenhydrogen atomsatoms attachedattached toto it.it. δ+ δ- δ+ δ- δ+ δ- HCl HOH ICl C H H H CCC+ > C +>>CC+ HC+ C C H H StereochemistryStereochemistry ►► XX-- attacksattacks anan achiralachiral carbocationcarbocation H + Me H X X- Et Et Me racemic mixture HydrationHydration ofof AlkenesAlkenes ►► AdditionAddition ofof SulfuricSulfuric AcidAcid ►► NetNet result:result: MarkovnikovMarkovnikov additionaddition ofof waterwater toto anan alkenealkene ►► AdditionAddition ofof WaterWater HydrationHydration ofof AlkenesAlkenes ►► HydrationHydration andand DehydrationDehydration areare simplysimply reversereverse reactionsreactions ofof oneone otherother ►► CarbocationCarbocation rearrangementsrearrangements cancan occuroccur OxymercurationOxymercuration--DemercurationDemercuration ►► TheThe procedureprocedure givesgives highhigh yieldsyields ofof alcoholsalcohols andand avoidsavoids rearrangementsrearrangements ►► MarkovnikovMarkovnikov selectivityselectivity H H Hg(OAc) , H O H O H 2 2 H H H Hg(OAc) H O H H O H - H NaBH4, OH H H H Hg(OAc) H OxymercurationOxymercuration--DemercurationDemercuration ►► MechanismMechanism ƒƒ MercuricMercuric acetateacetate dissociationdissociation + Hg(OAc)2 Hg(OAc) + AcO- ƒƒ MercuryMercury--bridgedbridged carbocationcarbocation ((MarkovnikovMarkovnikov selectivity)selectivity) ►► PositivePositive chargecharge sharedshared andand notnot largelarge enoughenough forfor aa rearrangementrearrangement toto occuroccur H H H H +Hg(OAc) δ+ H H Hg(OAc) ƒƒ WaterWater attackattack δ+ H HH O H OO HH ++ HH H HH δ++ HH OO HH H O H HH HHH222OOO HH HH22OO H HH H Hg(OAc) Hg(OAc)Hg(OAc) Hg(OAc)Hg(OAc) δδ++ OxymercurationOxymercuration ofof anan AlkeneAlkene Hg(OCOCH3)2 R CH CH2 RCHCH2 Hg(OCOCH3) H2O OH NaBH4 RCHCH2 H OH MechanismMechanism ofof OxymercurationOxymercuration OCOCH3 slow Hg OCOCH3 H H Hg OCOCH + 3 _ +CH3COO Formation of Bridged Ion: step 1 StepStep 2:2: AttackAttack byby waterwater H .. H H O.. :O : + - H H H H Hg OCOCH H Hg OCOCH + 3 3 or H .. O.. H Hg OCOCH3 H StepStep 3:3: ReductionReduction H H : : O :O: H H H Hg OCOCH3 H H NaBH4 or or + Hg (ppt) H H .. .. O.. H O.. H Hg H OCOCH3 H H Another example H CH 3 slow H Hg(OCOCH ) CH3 3 2 CH3 H O 2 CH3 O H Hg OCOCH3 25° C + H : HO.. H H + CH CH3 3 - H H OH CH3 CH3 H Hg OCOCH 3 Hg OCOCH + 3 Continued next slide H H CH CH3 H 3 OH NaBH4 H OH CH CH3 3 H Hg OCOCH3 HydroborationHydroboration ofof anan AlkeneAlkene BH3 R CH CH B 3 RCHCH2 2 2 3 PreparationPreparation ofof DiboraneDiborane ether 2 B H + 3 NaBF 3 NaBH4 + 4 BF3 2 6 4 H H H H B B 2 B H H H H H Electron deficient DIBORANEDIBORANE ADDSADDS TOTO ALKENESALKENES ANTIANTI--MARKOVNIKOFFMARKOVNIKOFF substituent RR + stabilizes transient carbocation center BH H - hydride transfer electrophile H H BH sp2 H empty 2p concerted R orbital H Since there are 3 B-H B H bonds, addition can H syn anti-Markovnikoff occur three times addition (3 moles of alkene) Boron adds to the carbon with the most hydrogens (!) which is the reverse of the Markovnikoff Rule. ConcertedConcerted versusversus CarbocationCarbocation IntermediateIntermediate R δ+ R R + H B H H B H δ- - H H Concerted reaction, Carbocation intermediate no intermediate; would allow rotation