有機化學課件2OrganicCompounds

1CHAPTER2OrganicCompounds:AlkanesandTheirStereochemistry22.1DefinitionAlkanesareorganicmoleculesconsistingsolelyofcarbonandhydrogenatomslinkedbySinglebonds.Allthecarbonsaretetrahedralandsp3hybridized.Alkanesarestablemoleculesandunreactivetomostchemicalreagents.TheyhavethegeneralformulaCnH2n+22.1.1Alkanes2.1.2CycloalkanesCycloalkanesarecyclicalkanestructures.TheyhavethegeneralformulaCnH2n.Mostcycloalkanesareunreactivetochemicalreagents.However,Three-andfour-memberedringsarereactiveduetoringstrainandbehavelikealkenes.3Namesofstraight-chainalkanes4Somestraight-chainalkylgroups5**TypesofAlkylgroups

Classifiedbytheconnectionsiteacarbonattheendofachain[primary(伯)alkylgroup]acarboninthemiddleofachain[secondary(仲)alkylgroup]acarbonwiththreecarbonsattachedtoit[tertiary(叔)alkylgroup]

6Inearliertimes,whenfewpureorganicchemicalswereknown,newcompoundswerenamedatthewhimoftheirdiscoverer.Thus,urea(CH4N2O)isacrystallineSubstanceisolatedfromurine,andbarbituricacidisatranquilizingagentnamedbyitsdiscovererinhonorofhisfriendBarbara.Asthescienceoforganicchemistryslowlygrewinnineteenthcentury,sotoodidthenumberofknowncompoundsandtheneedforasystematicmethodofnamingthem.ThesystemofnomenclatureisthatdevisedbytheInternationalUnionofPureandAppliedChemistry(IUPAC).Locant-Prefix-Parent-Suffix**2.2NomenclatureLocant:wherearethesubstituentsandfunctionalgroupsPrefix:whatarethesubstituentsParent:howmanycarbonsSuffix:whatistheprimaryfunctionalgroups7Forthepresent,let’sseehowbranched-chainalkanesarenamed.Allbutthemostcomplexbranched-chainalkanescanbenamedbyfollowingfoursteps:Step1FindtheparenthydrocarbonFindthelongestcontinuouscarbonchaininthemoleculeandusethenameofthatchainastheparentname.thelongestchainmaynotalwaysbeobvious;youmayhaveto“turncorners”.(b)Iftwochainsofequallengtharepresent,choosetheonewithlargernumberofbranchpointsastheparent.Step2Numbertheatomsinthelongestchain(a)Beginningattheendnearerthefirstbranchpoint,numbereachcarbonatomintheparentchain.(b)Ifthereisbranchinganequaldistanceawayfrombothendsoftheparentchainbeginningnumberattheendnearerthesecondbranchpoint.Step3

Identifyandnumberthesubstituents.Assignanumber,orlocant,toeachsubstituenttolocateitspointofattachmenttotheparentchain(b)Iftherearetwosubstituentsonthesamecarbon,giveboththesamenumber,Theymustbeasmanynumbersinthenameastherearesubstituents.Step4Writethenameasasingleword8Forexample9101112Alkanesaresometimesreferredtoasparaffins,awordderivedfromtheLatinparumAffinismeaning”slightaffinity.”Thistermaptlydescribestheirbehavior,foralkanesshowlittleaffinityforothersubstancesandareinerttomostlaboratoryreagents.Theydo,however,reactwithoxygen,chlorineandafewothersubstancesunderappropriateconditions.ThereactionofalkaneswithO2occursduringcombustioninanengineorfurnacewhenalkanesisusedasafuel.Carbondioxideandwaterareformedasproducts,andalargeamountofheatisreleased.Forexample,methane(naturalgas)reactswithoxyg-genaccordingtotheequation(890KJ/mol):2.3PropertiesofAlkanes13

Boilingpointsandmeltingpointsincreaseassizeofalkaneincreases,

Branchedoneshavelowerb.p.thantheirunbranchedisomers.[CH3CH2CH2CH3:0℃;(CH3)2CHCH3:-12℃]14InitiationreactionReactionmechanismofAlkaneswithCl2

-----FreeRadicalChainReactionStep1ChainpropagationStep2ChainterminationStep3h15

Conformersinterconverttoorapidlytobeisolatedandastructureisanaverageofconformers

Representingthreedimensionalconformersintwodimensionsisdonewithstandardtypesofdrawings

**2.4Conformations(構(gòu)象)ofEthane

16(重疊式)(交叉式)171819202122CxHyCl

?232.5DrawingChemicalStructure

2-甲基戊烷:C6H14(CH3)2CHCH2CH2CH324Carbonskeletondiagrams252.6

Cycloalkanes

環(huán)烷烴

**環(huán)烷烴的命名:Findtheparent找出母體Numberthesubstitute給取代基編號

261

乙基環(huán)戊烷(ethylcyclopentane)2

1-甲基-4-異丙基環(huán)己烷(1-methyl-4-isopropylcyclohexane3

2-環(huán)戊基己烷(cyclopentylhexane)4

反-1,4-二甲基環(huán)己烷(trans-1,4-dimethylcyclohexane)123427**2.7

Cis-transisomerizmincycloalkanes環(huán)烷烴的順―反異構(gòu)現(xiàn)象

28cis-1,2-dimethylcyclopropanetrans-1,2-dimethylcyclopropanecis-1-ethyl-3-methylcyclohexanecis-3-methylcyclohexylethanecis-1-甲基-3-乙基環(huán)己烷29**2.8Conformationsof

SomeCycloalkanes

3-memberedringmusthaveplanarstructure,SymmetricalwithC–C–Cbondanglesof60°,Requiresthatsp3

basedbondsarebent(andweakened),allC-Hbondsareeclipsed.Cyclobutaneandcyclopentanehavelessanglestrainthancyclopropane,theyareslightlypuckeredratherthanflat.30

Bondlength(鍵長)strain:thebonddistancesaredifferentfromthenormalvalues;

Angle(角)strain:destorsionofbondanglefromtheidealvalue;

Torsional(扭轉(zhuǎn))strain:torsionanglebetweenadjacentbondsareotherthan60°.

VanderWaals（范氏）strain(sterichindrance)

:atomsorgroupsonnonadjacentatomsaretooclosetooneanother

Straineffect有機分子中的張力313233

Thenatureofringstrain環(huán)張力的種類AnglestrainTorsionalstrainStericstrainBondlengthstrain34ConformationsofCyclohexane

Thechairconformation(椅式構(gòu)象)of

cyclohexaneringisfreeofanglestrainandtorsionalstrain

35HowtoDrawCyclohexane

36AxialandEquatorialBondsinCyclohexane

(環(huán)己烷上的a-鍵和e-鍵)

Thechairconformationhastwokindsofpositionsforsubstituentsonthering:axialpositionsandequatorialpositionsChaircyclohexanehassixaxial(a-,豎,直立)hydrogensperpendi