有机化学英文chapter2课件

OrganicChemistryWilliamH.BrownChristopherS.FooteBrentL.IversonAlkanesandCycloalkanesChapter2StructureHydrocarbon:acompoundcomposedonlyofcarbonandhydrogenSaturatedhydrocarbon:

ahydrocarboncontainingonlysinglebondsAlkane:asaturatedhydrocarbonwhosecarbonsarearrangedinanopenchainAliphatichydrocarbon:

anothernameforanalkaneStructureShapetetrahedralaboutcarbonallbondanglesareapproximately109.5°DrawingAlkanesLine-angleformulasanabbreviatedwaytodrawstructuralformulaseachvertexandlineendingrepresentsacarbonConstitutionalIsomerismConstitutionalisomers:compoundswiththesamemolecularformulabutadifferentconnectivityoftheiratomsexample:C4H10ConstitutionalIsomerismWorldpopulationisabout6,000,000,000Nomenclature-IUPACSuffix-anespecifiesanalkanePrefixtellsthenumberofcarbonatomsNomenclature-IUPACParentname:thelongestcarbonchainSubstituent:agroupbondedtotheparentchainalkylgroup:asubstituentderivedbyremovalofahydrogenfromanalkane;giventhesymbolR-Nomenclature-IUPAC5.Iftherearetwoormoreidenticalsubstituents,numberthechainfromtheendthatgivesthelowernumbertothesubstituentencounteredfirstindicatethenumberoftimesthesubstituentappearsbyaprefixdi-,tri-,tetra-,etc.usecommastoseparatepositionnumbersNomenclature-IUPAC6.Iftherearetwoormoredifferentsubstituents,listtheminalphabeticalordernumberfromtheendofthechainthatgivesthesubstituentencounteredfirstthelowernumberNomenclature-IUPAC7.Theprefixesdi-,tri-,tetra-,etc.arenotincludedinalphabetizationalphabetizethenamesofsubstituentsfirstandtheninserttheseprefixesNomenclature-CommonThenumberofcarbonsinthealkanedeterminesthenameallalkaneswithfourcarbonsarebutanes,thosewithfivecarbonsarepentanes,etc.iso-indicatesthechainterminatesin-CH(CH3)2;neo-thatitterminatesin-C(CH3)3ClassificationofC&HPrimary(1°)C:acarbonbondedtooneothercarbon1°H:ahydrogenbondedtoa1°carbonSecondary(2°)C:acarbonbondedtotwoothercarbons2°H:ahydrogenbondedtoa2°carbonTertiary(3°)C:acarbonbondedtothreeothercarbons3°H:ahydrogenbondedtoa3°

carbonQuaternary(4°)C:acarbonbondedtofourothercarbonsCycloalkanesGeneralformulaCnH2nfive-andsix-memberedringsarethemostcommonStructureandnomenclaturetoname,prefixthenameofthecorrespondingopen-chainalkanewithcyclo-,andnameeachsubstituentontheringifonlyonesubstituent,noneedtogiveitanumberiftwosubstituents,numberfromthesubstituentofloweralphabeticalorderifthreeormoresubstituents,numbertogivethemthelowestsetofnumbersandthenlistsubstituentsinalphabeticalorderCycloalkanesExample:namethesecycloalkanesBicycloalkanesBicycloalkane:analkanethatcontainstworingsthatsharetwocarbonsBicyclo[4.4.0]decane(Decalin)Bicyclo[4.3.0]nonane(Hydrindane)Bicyclo[2.2.1]heptane(Norbornane)BicycloalkanesNomenclatureparentisthealkaneofthesamenumberofcarbonsasareintheringsnumberfromabridgehead,alonglongestbridgebacktothebridgehead,thenalongthenextlongestbridge,etc.showthelengthsofbridgesinbrackets,fromlongesttoshortestIUPAC-General prop-en-e=propene eth-an-ol=ethanol but-an-one=butanone but-an-al=butanal pent-an-oicacid=pentanoicacid cyclohex-an-ol=cyclohexanol eth-yn-e=ethyne eth-an-amine=ethanamineConformationsConformation:anythree-dimensionalarrangementofatomsinamoleculethatresultsfromrotationaboutasinglebondNewmanprojection:awaytoviewamoleculebylookingalongacarbon-carbonsinglebondConformationsTorsionalstrainalsocalledeclipsedinteractionstrainstrainthatariseswhennonbondedatomsseparatedbythreebondsareforcedfromastaggeredconformationtoaneclipsedconformationthetorsionalstrainbetweeneclipsedandstaggeredethaneisapproximately12.6kJ(3.0kcal)/molConformationsDihedralangle(Q):theanglecreatedbytwointersectingplanesConformationsEthaneasafunctionofdihedralangleConformationsTheoriginoftorsionalstraininethaneoriginallythoughttobecausedbyrepulsionbetweeneclipsedhydrogennucleialternatively,causedbyrepulsionbetweenelectroncloudsofeclipsedC-Hbondstheoreticalmolecularorbitalcalculationssuggestthattheenergydifferenceisnotcausedbydestabilizationoftheeclipsedconformationbutratherbystabilizationofthestaggeredconformationthisstabilizationarisesfromthesmalldonor-acceptorinteractionbetweenaC-HbondingMOofonecarbonandtheC-HantibondingMOonanadjacentcarbon;thisstabilizationislostwhenastaggeredconformationisconvertedtoaneclipsedconformationConformationsanticonformationaconformationaboutasinglebondinwhichthegroupslieatadihedralangleof180°ConformationsStericstrain

(nonbondedinteractionstrain):thestrainthatariseswhenatomsseparatedbyfourormorebondsareforcedclosertoeachotherthantheiratomic(contact)radiiwillallowAnglestrain:strainthatariseswhenabondangleiseithercompressedorexpandedcomparedtoitsoptimalvalueThetotalofalltypesofstraincanbecalculatedbymolecularmechanicsprogramssuchcalculationscandeterminethelowestenergyarrangementofatomsinagivenconformation,aprocesscalledenergyminimizationConformationsconformationsofbutaneasafunctionofdihedralangleAntiButaneEnergy-minimizedanticonformationtheC-C-Cbondangleis111.9°andallH-C-Hbondanglesarebetween107.4and107.9°thecalculatedstrainis9.2kJ(2.2kcal)/molEclipsedButanecalculatedenergydifferencebetween(a)thenon-energy-minimizedand(b)theenergy-minimizedeclipsedconformationsis5.6kJ(0.86kcal)/molCyclopropaneanglestrain:theC-C-Cbondanglesarecompressedfrom109.5°to60°torsionalstrain:thereare6setsofeclipsedhydrogeninteractionsstrainenergyisabout116kJ(27.7kcal)/molCyclobutanepuckeringfromplanarcyclobutanereducestorsionalstrainbutincreasesanglestraintheconformationofminimumenergyisapuckered“butterfly”conformationstrainenergyisabout110kJ(26.3kcal)/molCyclopentanepuckeringfromplanarcyclopentanereducestorsionalstrain,butincreasesanglestaintheconformationofminimumenergyisapuckered“envelope”conformationstrainenergyisabout42kJ(6.5kcal)/molCyclohexaneChairconformation:themoststablepuckeredconformationofacyclohexaneringallbondC-C-Cbondanglesare110.9°allbondsonadjacentcarbonsarestaggeredCyclohexaneInachairconformation,sixHareequatorialandsixareaxialCyclohexaneForcyclohexane,therearetwoequivalentchairconformationsallC-Hbondsequatorialinonechairareaxialinthealternativechair,andviceversaCyclohexaneBoatconformation:apuckeredconformationofacyclohexaneringinwhichcarbons1and4arebenttowardeachothertherearefoursetsofeclipsedC-Hinteractionsandoneflagpoleinteractionaboatconformationislessstablethanachairconformationby27kJ(6.5kcal)/molCyclohexaneTwist-boatconformationapproximately41.8kJ(5.5kcal)/mollessstablethanachairconformationapproximately6.3kJ(1.5kcal)/molmorestablethanaboatconformationCyclohexaneEquatorialandaxialmethylconformationsMethylcyclohexaneG0axial--->equatorialgiventhedifferenceinstrainenergybetweenaxialandequatorialconformations,itispossibletocalculatetheratioofconformationsusingthefollowingrelationshipCis,TransIsomerismStereoisomers:compoundsthathavethesamemolecularformulathesameconnectivityadifferentorientationoftheiratomsinspaceCis,trans

isomers

stereoisomersthataretheresultofthepresenceofeitheraring(thischapter)oracarbon-carbondoublebond(Chapter5)IsomersrelationshipsamongisomersCis,TransIsomers1,2-DimethylcyclopentaneCis,TransIsomerism1,4-DimethylcyclohexaneCis,TransIsomerismtrans-1,4-Dimethylcyclohexanethediequatorial-methylchairconformationismorestablebyapproximately2x(7.28)=14.56kJ/molCis,TransIsomerismcis-1,4-DimethylcyclohexaneCis,TransIsomerismThedecalinsSteroidsThesteroidnucleusCholestanolBicycloalkanesNorbornanedrawnfromthreedifferentperspectivesBicycloalkanesAdamantanePhysicalPropertiesIntermolecularforcesofattraction(example)ion-ion(Na+andCl-inNaCl)ion-dipole(Na+andCl-solvatedinaqueoussolution)dipole-dipoleandhydrogenbondingdispersionforces(veryweakelectrostaticattractionbetweentemporarydipoles)PhysicalPropertiesLow-molecular-weightalkanes(methane....butane)aregasesatroomtemperatureHighermolecular-weightalkanes(pentane,decane,gasoline,kerosene)areliquidsatroomtemperatureHigh-molecular-weightalkanes(paraffinwax)aresemisolidsorsolidsatroomtemperaturePhysicalPropertiesConstitutionalisomershavedifferentphysicalpropertiesOxidationofAlkanesOxidationisthebasisfortheiruseasenergysourcesforheatandpowerheatofcombustion:heatreleasedwhenonemoleofasubstanceinitsstandardstateisoxidizedtocarbondioxideandwaterHeatofCombustionHeato