1492Ch29

Manahan,StanleyE.ORGANICCHEMISTRYEnvironmentalChemistryBocaRaton:CRCPressLLC,200029ORGANICCHEMISTRY____________________________________________________29.1.ORGANICCHEMISTRYMostcarbon-containingcompoundsareorganicchemicalsandareaddressedbythesubjectoforganicchemistry.Organicchemistryisavast,diversedisciplinebecauseoftheenormousnumberoforganiccompoundsthatexistasaconsequenceoftheversatilebondingcapabilitiesofcarbon.Suchdiversityisduetotheabilityofcarbonatomstobondtoeachotherthroughsingle(2sharedelectrons)bonds,double(4sharedelectrons)bonds,andtriple(6sharedelectrons)bondsinalimitlessvarietyofstraightchains,branchedchains,andrings.Amongorganicchemicalsareincludedthemajorityofimportantindustrialcom-pounds,syntheticpolymers,agriculturalchemicals,biologicalmaterials,andmostsubstancesthatareofconcernbecauseoftheirtoxicitiesandotherhazards.Pollutionofthewater,air,andsoilenvironmentsbyorganicchemicalsisanareaofsignificantconcern.Chemically,mostorganiccompoundscanbedividedamonghydrocarbons,oxygen-containingcompounds,nitrogen-containingcompounds,sulfur-containingcompounds,organohalides,phosphorus-containingcompounds,orcombinationsofthesekindsofcompounds.Eachoftheseclassesoforganiccompoundsisdiscussedbrieflyhere.Allorganiccompounds,ofcourse,containcarbon.VirtuallyallalsocontainhydrogenandhaveatleastoneC–Hbond.Thesimplestorganiccompounds,andthoseeasiesttounderstand,arethosethatcontainonlyhydrogenandcarbon.Thesecompoundsarecalledhydrocarbonsandareaddressedfirstamongtheorganiccompoundsdiscussedinthischapter.Hydrocarbonsareusedheretoillustratesomeofthemostfundamentalpointsoforganicchemistry,includingorganicformulas,structures,andnames.MolecularGeometryinOrganicChemistryThethree-dimensionalshapeofamolecule,thatis,itsmoleculargeometry,isparticularlyimportantinorganicchemistry.Thisisbecauseitsmoleculargeometry©2000CRCPressLLCdeterminesinpartthepropertiesofanorganicmolecule,particularlyitsinteractionswithbiologicalsystemsandhowitismetabolizedbyorganisms.Shapesofmoleculesarerepresentedindrawingsbylinesofnormal,uniformthicknessforbondsintheplaneofthepaper;brokenlinesforbondsextendingawayfromtheviewer;andheavylinesforbondsextendingtowardtheviewer.Theseconventionsareshownbytheexampleofdichloromethane,CH2Cl2,animportantorganochloridesolventandextractantillustratedinFigure29.1.ClCClHHClClHHCStructuralformulaofdichloromethaneintwodimensionsRepresentationofthethree-dimensionalstructureofdichloromethaneClatomstowardviewerHatomsawayfromviewerFigure29.1.Structuralformulasofdichloromethane,CH2Cl2;theformulaontherightprovidesathree-dimensionalrepresentation.29.2.HYDROCARBONSAsnotedabove,hydrocarboncompoundscontainonlycarbonandhydrogen.Themajortypesofhydrocarbonsarealkanes,alkenes,alkynes,andarylcompounds.ExamplesofeachareshowninFigure29.2.HCCCCHHCH3HHHHHHCCCCHHHHHHHCCH2-Methylbutane1,1-Butadiene(alkane)(alkene)Acetylene(alkyne)BenzeneNaphthalene(arylcompound)(arylcompound)Figure29.2.Examplesofmajortypesofhydrocarbons.AlkanesAlkanes,alsocalledparaffinsoraliphatichydrocarbons,arehydrocarbonsinwhichtheCatomsarejoinedbysinglecovalentbonds(sigmabonds)consistingoftwosharedelectrons(seeSection28.3).SomeexamplesofalkanesareshowninFigure29.2.Aswithotherorganiccompounds,thecarbonatomsinalkanesmay©2000CRCPressLLCformstraightchains,branchedchains,orrings.Thesethreekindsofalkanesare,respectively,straight-chainalkanes,branched-chainalkanes,andcycloalkanes.AsshowninFigure29.2,atypicalbranchedchainalkaneis2-methylbutane,avola-tile,highlyflammableliquid.Itisacomponentofgasoline,whichmayexplainwhyitiscommonlyfoundasanairpollutantinurbanair.Thegeneralmolecularformulaforstraight-andbranched-chainalkanesisCnH2n+2,andthatofcyclicalkanesisCnH2n.ThefourhydrocarbonmoleculesinFigure29.3contain8carbonatomseach.Inoneofthemolecules,allofthecarbonatomsareinastraightchainandintwotheyareinbranchedchains,whereasinafourth,6ofthecarbonatomsareinaring.1,4-DimethylcyclohexaneCCCCCCHHHHHHHHHHHHCHHHCHHH123456n-Octane2,5-Dimethylhexane654321CCCCCCHHHHHHHHCHHHCHHHHHCCCCCHHHHHHHHCHHHHHCHHCHHHCCCCCCCCHHHHHHHHHHHHHHHHHH2-Methyl-3-ethylpentaneFigure29.3.Structuralformulasoffourhydrocarbons,eachcontaining8carbonatoms,thatillustratethestructuraldiversitypossiblewithorganiccompounds.Numbersusedtodenotelocationsofatomsforpurposesofnamingareshownontwoofthecompounds.FormulasofAlkanesFormulasoforganiccompoundspresentinformationatseveraldifferentlevelsofsophistication.Molecularformulas,suchasthatofoctane(C8H18),givethenumberofeachkindofatominamoleculeofacompound.AsshowninFigure29.3,however,themolecularformulaofC8H18mayapplytoseveralalkanes,eachoneofwhichhasuniquechemical,physical,andtoxicologicalproperties.Thesedifferentcompoundsaredesignatedbystructuralformulasshowingtheorderinwhichtheatomsinamoleculearearranged.Compoundsthathavethesamemolecularbutdifferentstructuralformulasarecalledstructuralisomers.OfthecompoundsshowninFigure29.3,n-octane,2,5-dimethylhexane,and2-methyl-3-ethylpentanearestructuralisomers,allhavingtheformulaC8H18,whereas1,4-dimethylcyclo-hexaneisnotastructuralisomeroftheoth