郑州大学 有机化学第二章 烷烃

Manyanimals,especiallyinsects,communicatewithother

membersoftheir

speciesbasedontheodors

ofpheromones.1)

Pheromonesaresecreted(藏匿，分泌)byinsectsinextremelysmallamountsbut

theycancauseprofoundandvariedbiologicaleffects.2)

Pheromonesareusedassexattractants(性吸引剂)

incourtship(求偶),warning

substances,or

“aggregation(集合)

compounds”(tocausemembersoftheir

speciestocongregate(聚集)).Pheromones(信息素):CommunicationbyMeansofChemicals3)

Pheromonesareoftenrelativelysimplecompounds.CH3(CH2)9CH3

(cockroach(蟑螂)

aggregation

pheromone)(CH3)2CH(CH2)14CH3

(sexattractantoffemale

tigermoth灯蛾)5)Manyinsectsexattractantshavebeensynthesizedandareusedto

lureinsectsintotrapsasameansofinsectcontrol.4)

Muscalureisthesexattractantofthecommonhousefly(家蝇)

(Musca

domestica).chain~(链烃)Chapter2Alkaneshydrocarbons(碳氢化合物—烃)aliphatic~(脂肪烃)

saturatedaliphatic~(饱和脂肪烃)alkanes(烷烃)unsaturatedaliphatic~alkenes(烯烃)alkynes

(炔烃)cyclic~(环烃)alicyclic~(脂环烃)aromatic~(芳香烃)1.Homologousseriesandconstitutionalisomersofalkanes(烷烃的同系列与构造异构)1.1Homologousseries

Hybridization?Bonding?1.2Structure1.3Constitutionalisomers（构造异构体）structureconstitution(构造)configuration(构型)conformation(构象)Orderofatomicconnectionsthatdefinesamolecule

ArrangementofatomsthatcharacterizesaparticularstereoisomerDifferentarrangementsofatomsthatcanbeconvertedintooneanotherbyrotationaboutsinglebondsconstitutionalformulaconfigurationalformulaconstitutionalisomers(构造异构体)1.4Classesofcarbonatomsandhydrogenatoms(碳原子和氢原子的类型)primary(伯)secondary(仲)tertiary(叔)quarternary(季)2.Nomenclatureofalkanes(烷烃的命名)2.1Commonnames(普通命名法)methane甲烷ethane乙烷propane丙烷n-butane正丁烷n-pentane正戊烷n-hexane正己烷n-heptane正庚烷n-octane正辛烷n-nonane正壬烷n-decane正癸烷n-undecane正十一烷...straightchain(直链)Branchedchain(支链)?isobutane异丁烷isopentane异戊烷neopentane新戊烷5constitutionalisomers?IUPAC(internationalunionofpureandappliedchemistry)namesSystematicnames(系统命名法)2.2Systematicnames(系统命名法)2.2.1Fundamentalknowledge(基础知识)methane甲烷ethane乙烷propane丙烷n-butane正丁烷n-pentane正戊烷n-hexane正己烷n-heptane正庚烷n-octane正辛烷n-nonane正壬烷n-decane正癸烷n-undecane正十一烷...straightchain2.2.2Alkylgroups(烷基)-ane

-yl(alkanealkyl)Methyl甲基

Ethyl乙基n-Butyl正丁基n-Propyl正丙基isopropyl异丙基1-methylethyl1-甲基乙基i-Pr

isobutyl异丁基2-methylpropyl2-甲基丙基i-Butert-butyl叔丁基1,1-dimethylethyl1,1-二甲基乙基t-Busec-butyl仲丁基1-methylpropyl1-甲基丙基s-Buneopentyl新戊基2,2-dimethylpropyl2,2-二甲基丙基仲某基异某基叔某基2.2.3Nomenclature(命名)1)Selectastheparentstructurethelongestcontinuouschain.2)Numberthecarbontowhichthealkylgroupisattached.3)Name5-butyl-3,5,8-trimethylundecane3,5,8-三甲基-5-丁基十一烷4-甲基-6-乙基癸烷6-ethyl-4-methyldecaneasystemofrulesbasedonatomicnumber.Sequencerule(次序规则)4-甲基-8-异丙基十一烷4-isopropyl-8-methylun-decane-H（氢）<-D（氘）<-CH3（甲基）<-CH2CH3（乙基）<-CH2CH2CH3（丙基）<-CH2C6H5（苯甲基、苄基）<-CH(CH3)2（异丙基）<-CH=CH2（乙烯基）<-C(CH3)3（叔丁基）<-C6H5（苯基）<-C≡CH（乙炔基）<-CH2NH2（氨甲基）

<-C≡N（氰基）<-CH2OH（羟甲基）<-CHO（醛基、甲酰基）<-COCH3（乙酰基）<-COOH（羧基）<-COOCH3（甲氧羰基、甲酯基）<-NH2（氨基）<-NHCHO（甲酰氨基）<-NHCOCH3（乙酰氨基）<-N(CH3)2（二甲氨基）<-N+≡N（重氮基）<-NO（亚硝基）<-NO2（硝基）<-OH（羟基）<-OCH3（甲氧基）<-OCOH（甲酰氧基）<-OCOCH3（乙酰氧基）<-F（氟）<-SH（巯基）<-SO3H（磺酸基）<-Cl（氯）<-Br（溴）<-I（碘）

2,7,9-三甲基-6-异丁基十一烷2,7,9-三甲基-6-(2-甲丙基)十一烷Englishname??3-甲基-5-乙基-4-丙基庚烷Englishname?2,5-二甲基-4-异丁基庚烷Whenyourmusclescontractitislargelybecausemany

C–Csigma

(single)bondsareundergoing

rotation(conformational

changes构象转变)ina

muscleproteincalled

myosin(肌球蛋白).Nanotubes,anewclassofcarbon-basedmaterialswith

strengthroughly

onehundredtimesthatofsteel,alsohave

anexceptionaltoughness.Thepropertiesofthesematerialsdependsonmanythings,but

centralto

themiswhetherornotrotationispossiblearound

C–Cbonds.3.Conformationsofalkanes(烷烃的构象)3.1EthaneConformations:thetemporarymolecularshapes

thatresult

from

rotationsofgroupsaboutsinglebonds.Thestaggeredconformation(交叉式构象)

ofethane

Staggeredconformation:allowsthemaximumseparationoftheelectronpairsofthesixC—H

bondshasthelowestenergy

moststableconformation.伞形式锯架式纽曼式Theeclipsedconformation(重叠式构象)ofethaneEclipsedconformation:

maximumrepulsiveinteraction

betweentheelectronpairsofthe

sixC—Hbondshasthehighestenergy

leaststableconformation.伞形式锯架式纽曼式Potentialenergy(势能)changesthataccompanyrotationofgroupsaboutthecarbon-carbonbondofethane.Conformationsinwhichthetorsionanglesbetweenadjacentbondsareotherthan60ºaresaidtohavetorsionalstrain(扭转张力).V.Pophristic,L.Goodman.Hyperconjugationnotstericrepulsionleadstothestaggeredstructureofethane.Nature2001,411,565-568.

1)Inethanethedifferenceinenergybetweenthe

staggeredandeclipsedconformationsis12KJ/mol2)Unlessthetemperatureisextremelylow(−250℃),many

ethanemolecules(atanygivenmoment)willhaveenoughenergyto

surmountthisbarrier.3)Anethanemoleculewillspendmostofitstimeinthelowest

energy,staggeredconformation,orina

conformationverycloseto

beingstaggered.Many

timeseverysecond,itwillacquireenoughenergy

throughcollisionswithothermoleculestosurmountthe

torsionalbarrierandwillrotatethroughan

eclipsedconformation.4)Intermsofalargenumberofethanemolecules,

mostofthe

molecules(atanygivenmoment)will

beinstaggeredornearly

staggeredconformations.3.2ButaneImportantconformationsofbutaneAnti(对位交叉式)eclipsed(部分重叠式)gauche(邻位交叉式)eclipsed(全重叠式)EnergychangesthatarisefromrotationabouttheC2–C3bondofbutanetorsionalstrain/vanderWaalsrepulsion

force1)Theanticonformation(I):doesnothavetorsionalstrain

moststable.2)Thegaucheconformations(IIIandV):thetwomethylgroupsarecloseenoughtoeachother

thevanderWaalsforcesbetweenthemarerepulsive.

3)Theeclipsedconformation(II,IV,andVI):energymaxima

II,IVandVIhavetorsionalstrainandvanderWaalsrepulsionsarisingfromtheeclipsedmethylgroupandhydrogenatoms;IV

hasthegreatestenergyduetothelargevanderWaalsrepulsion

forcearisingfromtheeclipsedmethylgroups.4)Theenergybarriersarestilltoosmalltopermitisolationofthegaucheandanticonformationsatnormaltemperatures.EnergychangesthatarisefromrotationabouttheC2–C3bondofbutane1,2-二溴乙烷(对位交叉式构象约占84％)乙二醇(主要为邻位交叉式构象)SirDerekH.R.Barton(1918-1998,formerlyDistinguished

Professorof

ChemistryatTexasA&MUniversity)andOdd

Hassell(1897-1981,formerlyChairofPhysical

Chemistryof

OsloUniversity)sharedtheNobelprizein1969“fordevelopingandapplyingtheprinciplesofconformationinchemistry.”4.Physicalproperties(物理性质)5.有机反应中的热力学(thermodynamics)与动力学(kinetics)∆Gϴ=-RTInK=∆Hϴ-

T∆Sϴ∆Hϴ—焓变，是在标准状态下生成物与反应物焓之差，基本上是反应物与生成物之间的键能差，即所有形成新键的键能之和减去所有断裂键的键能之和。∆Sϴ—熵变，是在标准状态下生成物与反应物熵之差。熵可以看做是体系内的混乱度，因此熵变也就是在反应过程中体系内熵的变化，混乱度增加，∆Sϴ为正值，对反应有利；混乱度减少，∆Sϴ为负值，对反应不利。6.Reactions(反应)Alkanesaregenerallyinerttomanychemicalreagents.

C—CbondsarequitestrongC—Hbondsofalkanesareonlyslightlypolarized

Alkanesaregenerallyunaffectedbymostbases

Alkanemoleculeshavenounsharedelectronstooffer

sitesforattackbyacids

Reactivityofalkanes:1)Alkanesreactvigorouslywithoxygenwhenan

appropriatemixtureisignited(点燃)——

combustion(燃烧)(oxidation).2)Alkanesreactwithchlorineandbromine

under

heatorlight,andtheyreact

explosively

withfluorine——halogenation(卤化)6.1Combustion(燃烧)6.2Pyrolysis(热解)“cleavagebyheat”Hydrolysis(水解)(“cleavagebywater”)freeradical(自由基)Cracking(裂解)Themorevolatile,lower-molecular-weighthydrocarbonsareusefulasautomotivefuelsandasasourceofpetrochemicals.Freeradical(intermediate)Production(产生):Energymustbesuppliedbyheatingorby

irradiation(照射)withlighttocausehomolysis(均裂)ofcovalentbondsinthegasphase(气相)orinanonpolarsolvent(非极性溶剂).Reactivity(活性):

Almostallsmallradicalsareshort-lived,highlyreactivespecies.Stability(稳定性):ArCH2·，CH2=CHCH2·，3º>2º>1º>CH3·>Ar·，CH2=CH

·

Configuration(构型):

theCH3radicalisplanar(sp2

hybridizedcarbon)6.3Autoxidation(自动氧化)R-HReactivity(活性):3º>2º>1º

TheO–Obondofanalkylhydroperoxideisquiteweak,anditcanbreakand

produceradicalsthatcaninitiateotherchains:RO–OH

RO•+•OHBenzoylPeroxide(过氧化苯甲酰)Benzoylperoxideisanorganiccompoundintheperoxidefamily.Itconsistsoftwobenzoylgroupsbridgedbyaperoxidelink.Theoxygen-oxygenbondinperoxidesisweak.Thusbenzoylperoxidereadilyundergoeshomolysis,formingfreeradicals:

(C6H5CO)2O2→2C6H5COO•Benzoylperoxideisusedasaradicalinitiatortoinducepolymerizations.Othermajorapplicationsincludetreatingacne(痤疮,粉刺),dyeinghair,whiteningteeth,andbrighteningflour.TheFDA(theFoodandDrugAdministration)eventuallyclassifiedbenzoylperoxideas“safetyunknown”.especiallysusceptibletoabstractionbyO2radical(Lin•)autoxidationhydroperoxiderancidity(酸败)Autoxidationoccursinthebodywhichmaycauseirreversible

damage.

linoleicacid(亚油酸)(asanester)Antioxidants(抗氧剂)Autoxidationisinhibitedbyantioxidants，whichcanrapidly“trap”peroxylradicalsbyreactingwiththemtogivestabilizedradicalsthatdonotcontinuethechain.VitaminE

VitaminC

BHT:addedtofoodstopreventautoxidation

Therearetworeasonswhysomeradicalsaremorepersistentthanothers:(1)sterichindrance;(2)electronicstabilization.Manyofthemoleculesthatmakeupthestructureofhumantissuearesusceptibletohomolysisinintenselight,andthebodymakesuseofsophisticatedchemistrytoprotectitselffromtheactionofthereactiveradicalproducts.VitaminEplaysanimportantroleinthe‘taming’oftheseradicals:abstractionofHfromthephenolichydroxylgroupproducesarelativelystableradicalthatdoesnofurtherdamage.Polydimethylsiloxane(PDMS,聚二甲基硅氧烷)PDMSisthemostwidelyusedorganicpolymer,andisparticularlyknownforitsunusualflowproperties.Itsapplicationsrangefromcontactlenses(隐形眼镜)toelastomers(弹性体)。AccordingtotheHandbookofFoodAdditives,PDMSisasuspectedcarcinogen(致癌物)andanestablishedmutagen(诱变剂).BetyouneverthoughtthosewereinyourchickenMcNuggets!AccordingtoAConsumer'sDictionaryofFoodAdditives,TBHQcancomprisenomorethan0.02percentoftheoilinanugget.IngestingasinglegramofTBHQcancause“nausea,vomiting,ringingintheears,delirium(精神错乱),asenseofsuffocation,andcollapse.”IngestingfivegramsofTBHQcankill.tert-Butylhydroquinone(TBHQ,特丁基对苯二酚)6.4Nitration(硝化)(Substitution)6.5Sulfonation(磺化)(Substitution)Reactivity:F2>Cl2>Br2>>I2Fluorineisanextremelyaggressiveoxidizingagent,anditsreactionwithalkanesisstrongly

exothermic(放热的)anddifficulttocontrol.Chlorinationofalkanesislessexothermicthanfluorination,andbrominationlessexothermicthanchlorination.Iodineisuniqueamongthehalogensinthatitsreactionwithalkanesisendothermic(吸热的).6.6Halogenation(卤化)(Substitution)6.6.1Chlorinationofmethane(甲烷的氯化)Mechanism(机理)(链引发)(链增长)（c）Chain-terminatingstep