天津大学,高等有机化学,第二章芳香性

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1、第二章芳香性(Aromaticity)AromaticityisinventedtoaccountfortheunusualstabilityofanimportantclassoforganicmoleculeswithcyclicconjugationsystemsQualification:Cyclicconjugationsystem;4n+2лelectrons;Coplanar新定义：纬向分子（diatropic)——维持抗磁环电流2.1芳香化合物（一）苯（benzene)一、含苯芳香体系(benzenearomatichydrocarbonsystem)稳定性

2、：（二）稠环芳烃萘（naphthalene）共振能：255KJ/mol1.36Å1.415Å蒽（anthracene）共振能：351KJ/mol菲（phenanthrene）共振能：385KJ/mol二、杂芳香体系（heterocyclicaromaticsystem）121杂芳香化合物中键长并未完全平均化三、芳香离子（aromaticion）Resonanceenergy:100-113KJ/molmp=221℃μ=0.8D6.3D四、多电子芳香体系4n+2电子里氢0.00ppm,-7.88ppm,外氢7.6ppmPlanarityResonanceenergy:155K

3、J/molTheC—Cbonddistancesarenotequal:12innerbondsofabout1.38Åand6outerbondsofabout1.42ÅThe4n+2systemsarearomaticiftheycanbeplanar,aromaticitydecreaseswithdecreasingplanarity.五、其他芳香体系富勒烯（Fullerene)Curl、KrotoandSmalley1996NobelPrizeConclusionThepresenceofadiamagneticringcurrent(diatropic)Equa

4、lorapproximatelyequalbonddistancesPlanarityChemicalstabilityTheabilitytoundergoaromaticsubstitution2.2反芳香化合物(Antiaromaticcompounds)Ifcompoundsaremuchlessstable,theyarenotonlynonaromaticbutactuallyantiaromatic！Thechiefcriterionforantiaromaticityistheprensenceofaparamagneticringcurrent,which

5、causesprotonsontheoutsideoftheringtobeshiftedupfieldwhileanyinnerprotonsareshifteddownfield.(paratropic)Whentheclosedloopcontains4nelectrons,themoleculeisdestabilizedbyresonance.Antiaromaticitywillbemaximumwhenthemoleculeisplanarandwhenbonddistancesareequal.一、四电子体系环丁二烯衍生物Cyclobutadieneisre

6、ctangular,isnotsquare室温下能分离到的环丁二烯衍生物有：δ5.38Push-pulleffect环辛四烯(cyclooctatetraene)二、八电子体系单键：1.46A°双键：1.33A°Thereasonforthelackofplanarityisthataregularoctagonhasanlgesof135o,whilesp2anglesaremoststableat120o.Toavoidthestrain,themoleculeassumesanonplanarshape,inwhichorbitaloverlapisgreatlydi

7、mished.Tub-shaped[12]轮烯三、多电子体系4n电子[16]轮烯下列物质有芳香性的是：吡啶和吡咯哪个碱性强，为什么？下列化合物的1HNMR谱图上有几组信号，都在什么位置？