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生物化学ChapterArenesandAromaticity公开课一等奖优质课大赛微课获奖课件.pptx

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Chapter11ExercisesArenesarehydrocarbonsbasedonthebenzeneringasastructureunit.§11.1BenzaneSomehistory芳烃AromaticHydrocarbon苯和脂肪烃基取代苯只含有一个苯环，称为单环芳烃。苯环上能够是一元取代，也能够是多元取代；脂肪烃基能够是饱和，也能够是不饱和。比如：Thearomaticcharacterofbenzeneinfersaninherentstabilitytothesystem.Asaresult,benzeneisnotparticularlyreactivecomparedtoalkenes.Thisstabilitycanbeexpressedbytheresonanceenergy,whichforbenzeneisabout36kcal/mol环己烯与苯对比氢化热比较(KJ/mole)Heatofhydrogenationofcyclogenationofcyclohexene,1,3-cyclohexadiene,ahypothetical1,3,5-cyclohextriene,andbenzene.(KJ/mole)ResonanceEnergy共振能苯分子共振能§11.3KekuléandtheStructureofBenzeneBenzenehastheshapeofaregularhexagon.Inwhichall6Catomsin“aromatic”ringaresp2hybridised,withremaining6e-inunhybridisedporbitalsdelocalisedoverentirering,formingdoughnut/torusshapede-cloudsabove&belowringplaneAll12atomsinbenzene,C6H6,lieinthesameplane.Benzenehasaplanar,cyclic,conjugatedstructure.IfonedrawsbenzeneasalternatingC=CandC-CthenthetwodifferentKekuléstructuresareobtained.Thesearetwoequallyvalidresonancecontributors.Alternatively,thesetwoformscanbecombinedintheresonancehybridandthepsystemrepresentedbyacircleasintheRobinsonstructure.NotethatalloftheC-Cbondsare1.4Å(betweentypicalC=CandC-Cdistances).140pmStructure§11.3AResonanceDescriptionofBondinginBenzeneKekulé两种结构式符合共振条件：两种结构式仅在电子排列上结构不同依据共振理论,苯是Ⅰ，Ⅱ杂化体，因为二式完全等同，因此含有相同稳定性，对杂化体参加程度相等,共振作用大大提升了苯识所引发稳定性Circle-in-a-ringnotationstandsforresonancedescriptionofbenzene(hybridoftwoKekuléstructures).§11.4AnOrbitalHybridizationModelofBondinginBenzene碳上未参与杂化轨道电子与相邻碳上电子产叠，形成平面上下两个连续面包圈形电子云Themoreredanareais,thehighertheelectrondensityandthemoreblueanareais,thelowertheelectrondensity.Notethenucleophiliccharacterofthearomaticpsystem.Benzeneismuchmorestablethanwouldbeexpectedbasedoncalculationsfor“cyclohexatriene”Areasonablepredictionfortheheatofhydrogenationofhypotheticalcyclohexatrieneis-360kJmol-1(3timesthatofcyclohexene,-120kJmol-1)Theexperimentallydeterminedheatofhydrogenationforbenzeneis-280mol-1,152kJmol-1morestablethanhypotheticalcyclohe