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1、1-1-1 1Organic ChemistryWilliamH.BrownWilliamH.BrownWilliamH.BrownChristopherS.FooteChristopherS.FooteChristopherS.FooteBrentL.IversonBrentL.IversonBrentL.Iverson1-1-2 2CovalentBonding&ShapesofMoleculesChapter1Chapter1 1-1-3 3OrganicChemistryuThestudyofthecompoundsofcarbonuOver10millioncompoundshave
2、beenidentifiedabout1000newonesareidentifiedeachday!uCisasmallatomitformssingle,double,andtriplebondsitisintermediateinelectronegativity(2.5)itformsstrongbondswithC,H,O,N,andsomemetals1-1-4 4SchematicViewofanAtomasmalldensenucleus,diameter10-14-10-15m,whichcontainspositivelychargedprotonsandmostofthe
3、massoftheatomanextranuclearspace,diameter10-10m,whichcontainsnegativelychargedelectrons1-1-5 5ElectronConfigurationofAtomsuElectronsareconfinedtoregionsofspacecalledprincipleenergylevels(shells)eachshellcanhold2n2electrons(n=1,2,3,4.)1-1-6 6ElectronConfigurationofAtomsuShellsaredividedintosubshellsc
4、alledorbitals,whicharedesignatedbytheletterss,p,d,f,.s(onepershell)p(setofthreepershell2andhigher)d(setoffivepershell3andhigher).1-1-7 7ElectronConfigurationofAtomsuuAufbauPrinciple:AufbauPrinciple:orbitalsfillinorderofincreasingenergyfromlowestenergytohighestenergyuuPauliExclusionPrinciple:PauliExc
5、lusionPrinciple:onlytwoelectronscanoccupyanorbitalandtheirspinsmustbepaireduuHundsRule:HundsRule:whenorbitalsofequalenergyareavailablebuttherearenotenoughelectronstofillallofthem,oneelectronisaddedtoeachorbitalbeforeasecondelectronisaddedtoanyoneofthem1-1-8 8ElectronConfigurationofAtomsuThepairingof
6、electronspins1-1-9 9ElectronConfigurationofAtomsuTable1.3TheGround-StateElectronConfigurationofElements1-181-1-1010LewisDotStructuresuGilbertN.LewisuuValenceshell:Valenceshell:theoutermostoccupiedelectronshellofanatomuuValenceelectrons:Valenceelectrons:electronsinthevalenceshellofanatom;theseelectro
7、nsareusedtoformchemicalbondsandinchemicalreactionsuuLewisdotstructure:Lewisdotstructure:thesymbolofanelementrepresentsthenucleusandallinnershellelectronsdotsrepresentvalenceelectrons1-1-1111LewisDotStructuresuTable1.4LewisDotStructuresforElements1-181-1-1212LewisModelofBondinguAtomsbondtogethersotha
8、teachatomacquiresanelectronconfigurationthesameasthatofthenoblegasnearestitinatomicnumberanatomthatgainselectronsbecomesananionanionanatomthatloseselectronsbecomesacationcationtheattractionofanionsandcationsleadstotheformationofionicsolidsionicsolidsanatommayshareelectronswithoneormoreatomstocomplet
9、eitsvalenceshell;achemicalbondformedbysharingelectronsiscalledacovalentbondcovalentbondbondsmaybepartiallyionicorpartiallycovalent;thesebondsarecalledpolarcovalentbondspolarcovalentbonds1-1-1313ElectronegativityuuElectronegativity:Electronegativity:ameasureofanatomsattractionfortheelectronsitsharesw
10、ithanotheratominachemicalbonduuPaulingscalePaulingscalegenerallyincreaseslefttorightinarowgenerallyincreasesbottomtotopinacolumn1-1-1414FormationofIonsuAroughguideline:ionswillformifthedifferenceinelectronegativitybetweeninteractingatomsis1.9orgreaterexample:sodium(EN0.9)andfluorine(EN4.0)weuseasing
11、le-headed(barbed)curvedarrowtoshowthetransferofoneelectronfromNatoFinformingNa+F-,thesingle3selectronfromNaistransferredtothepartiallyfilledvalenceshellofF1-1-1515CovalentBondsuThesimplestcovalentbondisthatinH2thesingleelectronsfromeachatomcombinetoformanelectronpairthesharedpairfunctionsintwowayssi
12、multaneously;itissharedbythetwoatomsandfillsthevalenceshellofeachatomuThenumberofsharedpairsonesharedpairformsasinglebondtwosharedpairsformadoublebondthreesharedpairsformatriplebond1-1-1616PolarandNonpolarCovalentBondsuAlthoughallcovalentbondsinvolvesharingofelectrons,theydifferwidelyinthedegreeofsh
13、aringuWedividecovalentbondsintononpolarcovalentbondspolarcovalentbonds1-1-1717PolarandNonpolarCovalentBondsanexampleofapolarcovalentbondisthatofH-ClthedifferenceinelectronegativitybetweenClandHis3.0-2.1=0.9weshowpolaritybyusingthesymbolsd d d d+ +andd d d d- -,orbyusinganarrowwiththearrowheadpointin
14、gtowardthenegativeendandaplussignonthetailofthearrowatthepositiveend1-1-1818PolarCovalentBondsuuBonddipolemoment(Bonddipolemoment( ): ):ameasureofthepolarityofacovalentbondtheproductofthechargeoneitheratomofapolarbondtimesthedistancebetweenthenucleiTable1.7showsaveragebonddipolemomentsofselectedcova
15、lentbonds1-1-1919LewisStructuresuTowriteaLewisstructuredeterminethenumberofvalenceelectronsdeterminethearrangementofatomsconnecttheatomsbysinglebondsarrangetheremainingelectronssothateachatomhasacompletevalenceshellshowabondingpairofelectronsasasinglelineshowanonbondingpairofelectronsasapairofdotsin
16、asinglebondatomsshareonepairofelectrons,inadoublebondtheysharetwopairsofelectrons,andinatriplebondtheysharethreepairsofelectrons1-1-2020LewisStructures-Table1.3uInneutralmoleculeshydrogenhasonebondcarbonhas4bondsandnolonepairsnitrogenhas3bondsand1lonepairoxygenhas2bondsand2lonepairshalogenshave1bond
17、and3lonepairs1-1-2121FormalChargeuuFormalcharge:Formalcharge:thechargeonanatominamoleculeorapolyatomicionuToderiveformalcharge1.writeacorrectLewisstructureforthemoleculeorion2.assigneachatomallitsunshared(nonbonding)electronsandone-halfitsshared(bonding)parethisnumberwiththenumberofvalenceelectronsi
18、ntheneutral,unbondedatom1-1-2222FormalChargeuuExample:Example:DrawLewisstructures,andshowwhichatomineachbearstheformalcharge1-1-2323ExceptionstotheOctetRuleuMoleculescontainingatomsofGroup3Aelements,particularlyboronandaluminumAluminumchloride:FBFFClAlClCl6electronsinthevalenceshellsofboronandalumin
19、umBorontrifluoride:1-1-2424ExceptionstotheOctetRuleuAtomsofthird-periodelementshave3dorbitalsandmayexpandtheirvalenceshellstocontainmorethan8electronsphosphorusmayhaveupto101-1-2525ExceptionstotheOctetRulesulfur,anotherthird-periodelement,formscompoundsinwhichitsvalenceshellcontains8,10,or12electron
20、s1-1-2626FunctionalGroupsuuFunctionalgroup:Functionalgroup:anatomorgroupofatomswithinamoleculethatshowsacharacteristicsetofphysicalandchemicalpropertiesuFunctionalgroupsareimportantforthreereason;theyare1.theunitsbywhichwedivideorganiccompoundsintoclasses2.thesitesofcharacteristicchemicalreactions3.
21、thebasisfornamingorganiccompounds1-1-2727Alcoholsucontainan-OH(hydroxylhydroxyl)groupuEthanolmayalsobewrittenasacondensedcondensedstructuralformulastructuralformula1-1-2828Alcoholsalcoholsareclassifiedasprimary(1),secondary(2),ortertiary(3)dependingonthenumberofcarbonatomsbondedtothecarbonbearingthe
22、-OHgroup1-1-2929AlcoholstherearetwoalcoholswithmolecularformulaC3H8O1-1-3030Aminesucontainanaminogroupaminogroup;ansp3-hybridizednitrogenbondedtoone,two,orthreecarbonatomsanaminemayby1,2,or3CH3N HHCH3N HCH3CH3N CH3CH3Methylamine(a1amine)Dimethylamine(a2amine)Trimethylamine(a3amine):1-1-3131Aldehydes
23、andKetonesucontainacarbonyl(C=O)groupcarbonyl(C=O)group1-1-3232CarboxylicAcidsucontainacarboxyl(-COOH)groupcarboxyl(-COOH)group1-1-3333CarboxylicEstersuuEster:Ester:aderivativeofacarboxylicacidinwhichthecarboxylhydrogenisreplacedbyacarbongroup1-1-3434CarboxylicAmideuCarboxylicamidearboxylicamide,com
24、monlyreferredtoasanamideamide:aderivativeofacarboxylicacidinwhichthe-OHofthe-COOHgroupisreplacedbyanaminethesixatomsoftheamidefunctionalgrouplieinaplanewithbondanglesofapproximately1201-1-3535VSEPRuBasedonthetwinconceptsthatatomsaresurroundedbyregionsofelectrondensityregionsofelectrondensityrepeleac
25、hother1-1-3636VSEPRModeluuExample:Example:predictallbondanglesforthesemoleculesandions1-1-3737PolarandNonpolarMoleculesuTodetermineifamoleculeispolar,weneedtodetermineifthemoleculehaspolarbondsthearrangementofthesebondsinspaceuuMoleculardipolemoment(Moleculardipolemoment( ): ):thevectorsumoftheindiv
26、idualbonddipolemomentsinamoleculereportedindebyes(D)1-1-3838PolarandNonpolarMoleculesuthesemoleculeshavepolarbonds,buteachhasazerodipolemoment1-1-3939PolarandNonpolarMoleculesuthesemoleculeshavepolarbondsandarepolarmolecules1-1-4040PolarandNonpolarMoleculesformaldehydehaspolarbondsandisapolarmolecul
27、e1-1-4141ResonanceuFormanymoleculesandions,nosingleLewisstructureprovidesatrulyaccuraterepresentation1-1-4242ResonanceuLinusPauling-1930smanymoleculesandionsarebestdescribedbywritingtwoormoreLewisstructuresindividualLewisstructuresarecalledcontributingstructuresconnectindividualcontributingstructure
28、sbydouble-headed(resonance)arrowsthemoleculeorionisahybridofthevariouscontributingstructures1-1-4343ResonanceuuExamples:Examples: equivalentcontributingstructuresequivalentcontributingstructures1-1-4444ResonanceuuCurvedarrow:Curvedarrow:asymbolusedtoshowtheredistributionofvalenceelectronsuInusingcur
29、vedarrows,thereareonlytwoallowedtypesofelectronredistribution:fromabondtoanadjacentatomfromanatomtoanadjacentbonduElectronpushingisasurvivalskillinorganicchemistrylearnitwell!1-1-4545ResonanceuAllcontributingstructuresmust1.havethesamenumberofvalenceelectrons2.obeytherulesofcovalentbondingnomorethan
30、2electronsinthevalenceshellofHnomorethan8electronsinthevalenceshellofa2ndperiodelement3rdperiodelements,suchasPandS,mayhaveupto12electronsintheirvalenceshells3.differonlyindistributionofvalenceelectrons;thepositionofallnucleimustbethesame4.havethesamenumberofpairedandunpairedelectrons1-1-4646Resonan
31、ceuThecarbonateion,forexampleahybridofthreeequivalentcontributingstructuresthenegativechargeisdistributedequallyamongthethreeoxygens1-1-4747ResonanceuuPreference1:Preference1:filledvalenceshellsstructuresinwhichallatomshavefilledvalenceshellscontributemorethanthosewithoneormoreunfilledvalenceshellsG
32、reatercontribution;bothcarbonandoxygenhavecompletevalenceshellsLessercontribution;carbonhasonly6electronsinitsvalenceshell+CCH3OCH3OHHCHH1-1-4848ResonanceuuPreference2:Preference2:maximumnumberofcovalentbondsstructureswithagreaternumberofcovalentbondscontributemorethanthosewithfewercovalentbonds1-1-
33、4949ResonanceuuPreference3:Preference3:leastseparationofunlikechargestructureswithseparationofunlikechargescontributelessthanthosewithnochargeseparationLessercontribution(separationofunlikecharges)CH3-C-CH3CH3-C-CH3Greatercontribution(noseparationofunlikecharges)O -O:1-1-5050ResonanceuuPreference4:P
34、reference4:negativechargeonthemoreelectronegativeatomstructuresthatcarryanegativechargeonthemoreelectronegativeatomcontributemorethanthosewiththenegativechargeonthelesselectronegativeatom1-1-5151QuantumorWaveMechanicsuAlbertEinstein:E=hn n(energyisquantized)lighthasparticlepropertiesuLouisdeBroglie:
35、wave/particledualityuErwinSchrdinger:waveequation wavefunction,wavefunction, :asolutiontoasetofequationsthatdepictstheenergyofanelectroninanatomeachwavefunctionisassociatedwithauniquesetofquantumnumberseachwavefunctionoccupiesthree-dimensionalspaceandiscalledanorbitalorbital 22istheprobabilityoffind
36、inganelectronatagivenpointinspace1-1-5252Shapesof1sand2sOrbitalsuProbabilitydistribution( 2)for1sand2sorbitalsshowinganarbitraryboundarysurfacecontainingabout95%oftheelectrondensity1-1-5353ShapesofaSetof2pAtomicOrbitalsuThree-dimensionalshapesof2patomicorbitals1-1-5454MolecularOrbitalTheoryuElectron
37、sinatomsexistinatomicorbitalsuElectronsinmoleculesexistinmolecularorbitals(MOs)uUsingtheSchrdingerequation,wecancalculatetheshapesandenergiesofMOs1-1-5555MolecularOrbitalTheoryuRules:combinationofnatomicorbitals(mathematicallyaddingandsubtractingwavefunctions)givesnMOs(newwavefunctions)MOsarearrange
38、dinorderofincreasingenergyMOfillingisgovernedbythesamerulesasforatomicorbitals:Aufbauprinciple:fillbeginningwithLUMOPauliexclusionprinciple:nomorethan2e-inaMOHundsrule:whentwoormoreMOsofequivalentenergyareavailable,add1e-toeachbeforefillinganyoneofthemwith2e-1-1-5656MolecularOrbitalTheoryuTerminolog
39、ygroundstate=lowestenergystateexcitedstate=NOTlowestenergystate =sigmabondingMO *=sigmaantibondingMO =pibondingMO *=piantibondingMOHOMO=highestoccupiedMOLUMO=lowestunoccupiedMO1-1-5757MolecularOrbitalTheoryuSigma1sbondingandantibondingMOs1-1-5858MolecularOrbitalTheoryMOenergydiagramforH2:(a)groundst
40、ateand(b)lowestexcitedstate1-1-5959MolecularOrbitalscomputedsigmabondingandantibondingMOsforH21-1-6060MolecularOrbitalsupibondingandantibondingMOs1-1-6161MolecularOrbitalscomputedpibondingandantibondingMOsforethylene1-1-6262MolecularOrbitalscomputedpibondingandantibondingorbitalsforformaldehyde1-1-6
41、363HybridOrbitalsuTheProblem:bondingby2sand2patomicorbitalswouldgivebondanglesofapproximately90insteadweobservebondanglesofapproximately109.5,120,and180uASolutionhybridizationofatomicorbitals2ndrowelementsusesp3,sp2,andsphybridorbitalsforbonding1-1-6464HybridOrbitalsuHybridizationoforbitals(L.Paulin
42、g)thecombinationoftwoormoreatomicorbitalsformsanewsetofatomicorbitals,calledhybridorbitalsuWedealwiththreetypesofhybridorbitalsspsp3 3(onesorbital+threeporbitals)spsp2 2(onesorbital+twoporbitals)spsp(onesorbital+oneporbital)uOverlapofhybridorbitalscanformtwotypesofbondsdependingonthegeometryofoverla
43、p bondsbondsareformedby“direct”overlap bondsbondsareformedby“parallel”overlap1-1-6565sp3HybridOrbitalseachsp3hybridorbitalhastwolobesofunequalsizethesignofthewavefunctionispositiveinonelobe,negativeintheother,andzeroatthenucleusthefoursp3hybridorbitalsaredirectedtowardthecornersofaregulartetrahedron
44、atanglesof109.51-1-6666sp3HybridOrbitalsorbitaloverlappicturesofmethane,ammonia,andwater1-1-6767sp2HybridOrbitalstheaxesofthethreesp2hybridorbitalslieinaplaneandaredirectedtowardthecornersofanequilateraltriangletheunhybridized2porbitalliesperpendiculartotheplaneofthethreehybridorbitals1-1-6868Bondin
45、ginEthylene1-1-6969BondinginFormaldehyde1-1-7070spHybridOrbitalstwolobesofunequalsizeatanangleof180theunhybridized2porbitalsareperpendiculartoeachotherandtothelinecreatedbytheaxesofthetwosphybridorbitals1-1-7171BondinginAcetylene,C2H21-1-7272HybridOrbitals1-1-7373BondLengthsandBondStrengths1-1-7474CovalentBonds&ShapesofMoleculesEndChapter1EndChapter1
