Ch 3 - Structure and Stereochemistry of Alkanes

Ch 3 - Structure and Stereochemistry of Alkanes - Structure...

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3 Structure and StereoChem isTRy Of Alkanes W henever possible, we wILl study organIc chemIstry usIng famIlIes of compounds to organIze the mateRial. The pRopertIes and reactIons of the compounds in a famIly are sImilar± just as theiR stRuctuRes are simIlar² By consIdeRIng how the structural featuRes of a cLass of compounds determine their prop- eR³Ies± we can predict the propertIes and reac³Ions of sImilar new compounds´ ThIs oRganIzatIon elevates organic chemIstry fRom a catalog of many indIvIduaL com- pounds to a systematIc study of a few types of compounds. FamILies of organIc moLecuLes aRe cLassIµ¶ed according to theiR ReactIve paRts, called functional groups . · We consideRed some of the common functIonaL groups In SectIons 2-12 through 2-±4. An alkane is a hydRoc¸r¹on that contaIns onLy single bonds. ºhe aLkanes ¸re ³he sim» plest and least reac³ive class of oRganIc compounds because they contain onLy hydrogen and sp 3 hy¹ridIzed carbon, and they have no Reactive ¼unctional gRoups. Al³hough alkanes undeRgo ReactIons such as cRacking and combustion at hIgh temperatuRes, they ¸re much Less reac½ive than otheR cLasses of compounds havIng ¼unctIonal gRoups. We classify hydRocarbons according to theIR bondIng (SectIon 2²±2), as shown in Ta¹Le 3-±³ Alkanes have onLy singLe bonds. A hydRocaR¹on wIth a caR¹on¾caRbon dou¿ bLe bond (such as ethyLene) Is an alkene± Àf a hydrocaRbon has a caRbonÁcaR¹on tripLe ¹ond (LIke acetyLene), It Is an alKne. HydrocaR¹ons wIth aRomatic RIngs (resembLIng ¹enzene) aRe calLed aRmatic hydrOcarbons² TABLE 3-1 Summary of Hydrocarbon Classification Compound Type alkanes aLkenes a±\ynes aromatics Funcional Group none (no doubLe or tripLe bonds) " C = C / . ' -C ± C ² trIpLe bond I C ³ C ´ C µ benzene ring i ii µ C ¶ µ C · C ± Example CH3¸CH2²CH¹, propane CH2ºCH²CH3 » propene H²C±C ² CH3 » propyNe 3-1 Classification of Hydrocarbons (Review) 81
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82 Chapter 3: STrucTUre and StereochemisTry of Alkanes 3-2 MolecuLar FormuLas of Alkanes A hydrocarbon with no doubLe oR tRip±e bonds is said to be saturated because It has the maxImum numbeR of boNded hydrogens. ANotheR way to descRIbe alkanes, then, is as the c±ass of saturated hydrocarbons. Tab±e 3-2 shows the structures aNd formuLas of the fiRst ±0 unbRanched a±kanes² Any isomeRs of these compounds have the same moLecuLar foRmu±as eveN though theiR structures aRe diFeReNt² ³otice how the moLecuLar foRmu±as increase by two hydRogeN atoms each tIme a caRbon atom Is added² The structures of the aLkanes in TabLe 3²± are purpose±y wrItten as chaIns of -CH2- groups (methylene groups), teRmiNated at each eNd by a hydRogeN atom. This is the geNera± formuLa foR the unbRaNched (straight´chaiN) aLkaNes. These aLkaNes differ onLy by the Number of methy±ene gRoups in the chain² If the moLecu±e contains µ carbon atoms, it must contaIn (2N + 2) hydRogeN atoms. ¶Igure 3²1 shows how this patteRn appeaRs In stRuctures and how it ±eads to foRmu· ±as of the foRm C¸H2¹ + 2.
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This note was uploaded on 02/27/2010 for the course CHEM 140 taught by Professor Wade during the Spring '10 term at Whitman.

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Ch 3 - Structure and Stereochemistry of Alkanes - Structure...

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