Chapter 1 1 Chemical Bonding and Chemical Structure Organic Chemistry, 5th ed. Marc Loudon Eric J....
Transcript of Chapter 1 1 Chemical Bonding and Chemical Structure Organic Chemistry, 5th ed. Marc Loudon Eric J....
Chapter1ChemicalBondingandChemicalStructure
Organic Chemistry, 5th ed. Marc Loudon
Eric J. Kantorowski California Polytechnic State University San Luis Obispo, CA
Chapter1Overview
• 1.1Introduc,on• 1.2ClassicalTheoriesofChemicalBonding• 1.3StructureofCovalentCompounds
• 1.4ResonanceStructures• 1.5WaveNatureoftheElectron
• 1.6ElectronicStructureoftheHydrogenAtom
• 1.7ElectronicStructureofMoreComplexAtoms• 1.8AnotherLookattheCovalentBond:MolecularOrbitals
• 1.9HybridOrbitals
2
Organicchemistry
• Thebranchofsciencethatdealswithcompoundsthatcontaincarbon
• Vitalism:Onlybiologicalsystems(e.g.,plants,animals)couldproduceorganiccompounds
• Wohler’ssynthesisofurea(1828),begantounderminevitalism
31.1Introduc6on
WhyStudyOrganicChemistry?
• Organicchemistryliesattheheartofthemodernchemicalindustry
• Centraltomedicineandpharmacy
• Interfaceofphysicalandbiologicalsciences• Everydayapplica,ons:Plas,cs,tex,les,communica,ons,transporta,on,food,clothing,cosme,cs,etc.
41.1Introduc6on
ElectronsinAtoms
• Valenceshell:Theoutermostshellofelectronssurroundinganatom
• Atomsgainorlosevalenceelectronstoachievenoblegasconfigura,on
• Octetrule:Elementswanteightvalenceelectrons
• Chemistryhappensbecauseofthebehaviorofvalenceelectrons!
51.2ClassicalTheoriesofChemicalBonding
IonicCompounds
• Chemicalcompoundswithionspresent• Ionicbondsareomni‐direc6onal
• Candissociateintofreeions
61.2ClassicalTheoriesofChemicalBonding
CovalentBonds
• Whentwoatomsshareelectrons• Covalentbondsaredirec6onal• LewisStructuresuse“:”and“–”torepresentbonds
71.2ClassicalTheoriesofChemicalBonding
LewisStructures
• Nota,onforelectron‐pairbonds• Sharedelectrons(bonding)• Unsharedelectrons(non‐bonding=lonepairs)• Strivetosa,sfytheoctetrule(and2forH)
81.2ClassicalTheoriesofChemicalBonding
FormalCharge
• Thechargeassignedtoanatom• Findvalence#(=Group#ofatom)
• Subtract#ofunsharedelectrons• Subtracthalfofthebondingelectrons
91.2ClassicalTheoriesofChemicalBonding
ThePolarCovalentBond
• Unevensharingofelectronsinabond• ElectronegaDvitydeterminesdirec,on
101.2ClassicalTheoriesofChemicalBonding
ElectrostaDcPotenDalMaps
• Agraphicaldepic,onofelectrondistribu,on
111.2ClassicalTheoriesofChemicalBonding
DipoleMoment(µ)
• Dependsonchargesepara,onanddistance• µ=qr(avectorquan,ty)
121.2ClassicalTheoriesofChemicalBonding
BondPolarityandFormalCharge
• Formalchargeisonlyabookkeepingtool• Formalchargemayormaynotcorrespondtoactualcharge!
131.2ClassicalTheoriesofChemicalBonding
MolecularStructure
• AtomicconnecDvity:Howatomsinamoleculeareconnected
• Moleculargeometry:Howfarapartatomsareandhowtheyarearrangedinspace
• Knowingatomicconnec,vityandmoleculargeometryrevealstheoverallstructure
141.3StructuresofCovalentCompounds
MethodsforDeterminingMolecularGeometry
• X‐raycrystallography:Atomicarrangementofsolids
• ElectrondiffracDon:Atomicarrangementofgaseoussubstances
• Microwavespectroscopy:Structuralinfoofgaseoussubstances
• Nocomparablemethodsavailableforanalysisofaliquid
151.3StructuresofCovalentCompounds
MolecularGeometry
• Moleculargeometryinfluenceschemicalreac,vity
• Bondlength:distancebetweennuclei• Bondangle:anglebetweeneachpairofbonds
161.3StructuresofCovalentCompounds
BondLength
• Increaseswithatomsinhigherrows• Decreaseswithincreasingbondorder• Decreasestowardhigheratomicnumberalongarow
171.3StructuresofCovalentCompounds
BondAngle
• Bondanglesdetermineshape• Valence‐shellelectron‐pairrepulsion(VSEPR)• Usemolecularmodels!
• Line‐and‐wedgestructures
181.3StructuresofCovalentCompounds
CommonShapestoKnow
• Tetrahedron
• TrigonalPlanar
191.3StructuresofCovalentCompounds
CommonShapestoKnow
• Linear
• Trigonalpyramidal
201.3StructuresofCovalentCompounds
DihedralAngle
• Alsoknownasthetorsionalangle• Rota,oncanoccuralongsinglebonds
211.3StructuresofCovalentCompounds
ResonanceStructures
• AsingleLewisstructuremaynotbeenough• MoreLewisstructures=moreinfoonelectrondistribu,on(thesearenotinequilibrium!)
• The“true”electrondistribu,onisaweightedaverageoftheindividualcontributors
• Suchstructuresareresonance‐stabilized
221.4ResonanceStructures
QuantumViewoftheElectron
• Covalentchemicalbonds:Thesharingofoneormoreelectronpairsbetweentwoatoms
• Thismodelishighlyusefulbuthasitslimita,ons
• Quantummechanicsdescribesanalternate,moredetailedview
231.5WaveNatureoftheElectron
HeisenbergUncertaintyPrinciple
• Impossibletoknowtheposi,onandvelocityofapar,cle
• Notimportantforlargeobjects(cars,baseballs,andevenmolecules)
• Highlyimportantforverysmallobjects(electrons)
• Theloca,onofanelectronis“fuzzy”
241.5WaveNatureoftheElectron
Orbitals,QuantumNumbers,andEnergy
• Atomicorbital:Describesthewaveproper,esofanelectroninanatom
• Eachorbitalisdescribedby3quantumnumbers(n,l,ml)
251.6ElectronicStructureoftheHydrogenAtom
SpaDalCharacterisDcsofOrbitals
• 3‐Dorbitalpicture=90%probabilitylevel• Node:Adefinedregionofnoelectrondensity• 1sand2sorbitals:
261.6ElectronicStructureoftheHydrogenAtom
SpaDalCharacterisDcsofOrbitals
• Threedegenerateporbitals(px,py,pz)• Orthogonaltooneanother• 2porbital:
271.6ElectronicStructureoftheHydrogenAtom
ElectronConfiguraDon
• AuXauprinciple:Buildupprinciple• Electronspin(ms):+1/2(up)or‐1/2(down)
281.7ElectronicStructuresofMoreComplexAtoms
ElectronConfiguraDon
• Hund’srule:placeelectronsintodegenerateorbitalsbeforepairingthem
• Pauliexclusionprinciple:Notwoelectronscanhavethesamefourquantumnumbers
291.7ElectronicStructuresofMoreComplexAtoms
MolecularOrbitalTheory
• Combiningatomicorbitals(AOs)generatesmolecularorbitals(MOs)
• nAOs→nMOs
301.8AnotherLookattheCovalentBond:MolecularOrbitals
MolecularOrbitalTheory
• AddingAOsresultsinconstruc6veinterac,on• Remember:Orbitalsaredescribedbymathema6calfunc6ons‐theycanbeaddedandsubtracted
311.8AnotherLookattheCovalentBond:MolecularOrbitals
MolecularOrbitalTheory
• Subtrac,ngAOsresultsindestruc6veinterac,on
• Subtrac,nganAOisthesameasaddinganAOofoppositephase
321.8AnotherLookattheCovalentBond:MolecularOrbitals
OrbitalInteracDonDiagram
331.8AnotherLookattheCovalentBond:MolecularOrbitals
BondinginMethane
• TheMOpictureofmethanedistributeselectronsthroughouttheen,remolecule
• Totalelectrondensityinmethane:
341.9HybridOrbitals
ConstrucDngMethane
• Amoreuseful(butlessaccurate)pictureofbondinginmethanerequireshybridorbitals
• ThemixingprocessappliedtoAOstomakeMOsiscalledhybridizaDon
351.9HybridOrbitals
BondinginMethane
• Mixings+px+py+pz→Foursp3MOs
361.9HybridOrbitals
BondinginMethane
• Eachsp3MOcanthencombinewithaHatom
371.9HybridOrbitals
BondinginAmmonia
• Thehybridorbitalpictureaccommodatesmoleculeswithlonepairstoo(e.g.,:NH3)
381.9HybridOrbitals
BondinginAmmonia
• Thehybridorbitaldescrip,onofammonia• Note,thesmallrearlobesofeachsp3orbitalarecommonlyomioedforclarity
391.9HybridOrbitals