Carey_part_A习题答案

SolutionstoProblemsChapter11.1.a.Adipolarresonancestructurehasaromaticcharacterinbothringsandwouldbeexpectedtomakeamajorcontributiontotheoverallstructure.+–b.The“extra”polarityassociatedwiththesecondresonancestructurewouldcontributetothemolecularstructurebutwouldnotbeaccountedforbystandardgroupdipoles.N+O–ONHHN+N+–O–OHHc.Therearethreemajorfactorscontributingtotheoveralldipolemoments:(1)the-bonddipoleassociatedwiththeC−OandC−Nbonds;(2)the-bonddipoleassociatedwithdelocalizationofelectronsfromtheheteroatomtothering;and(3)thedipolemomentassociatedwiththeunsharedelectronpair(forO)orN−Hbond(forN).Allthesefactorshaveagreatermomenttowardratherthanawayfromtheheteroatomforfuranthanforpyrrole.Forpyrrole,theC−NdipoleshouldbelargerandtheN−Hmomentintheoppositedirectionfromfuran.Thesetwofactorsaccountforthereversalinthedirectionoftheoveralldipolemoment.TheAIMchargeshavebeencalculated.OHunsharedpairbondelectronselectronsONN–HdipolebondONAIMchargesNOHH–0.0080.027–1.3430.0850.567HH0.0620.532–1.5850.470–.008–.029HN12SolutionstoProblems1.2.a.Thenitrogenisthemostbasicatom.PhCH=N+PhHb.Protonationonoxygenpreservestheresonanceinteractionwiththenitrogenunsharedelectronpair.CH3CO+–HNH2CH3CO–HN+H2c.Protonationonnitrogenlimitsconjugationtothedienesystem.ProtonationonC(2)preservesamorepolarandmorestableconjugatediminiumsystem.ProtonationonC(3)givesalessfavorablecross-conjugatedsystem.N+HHHN+N+HHNHH+HHHHd.Protonationontheringnitrogenpreservesconjugationwiththeexocyclicnitrogenunsharedelectrons.NN+H3chargecanbedelocalizedchargeislocalizedonexocyclicnitrogenNNH2H+N+H2NH1.3.a.Thedipolarresonancestructurecontainingcyclopentadienideandpyridiniumringswouldbeamajorresonancecontributor.Thedipolemomentsandbondlengthswouldbeindicative.Also,theinter-ring“doublebond”wouldhaveareducedrotationalbarrier.C2H5NN+–C2H5b.ThedipolaroxycyclopropeniumstructurecontributestoalongerC−Obondandanincreaseddipolemoment.TheC=Ovibrationalfrequencyshouldbeshiftedtowardlowerfrequencybythepartialsingle-bondcharacter.ThecompoundshouldhavealargerpKafortheprotonatedform,reflectingincreasedelectrondensityatoxygenandaromaticstabilizationofthecation.3SolutionstoProblemsO–+PhPhOPhPhc.TherewouldbeashiftintheUVspectrum,theIRC=Ostretch,andNMRchemicalshifts,reflectingthecontributionfromadipolarresonancestructure.CHCCH3CH=CCH3O–+O1.4.a.Amidespreferplanargeometrybecauseoftheresonancestabilization.Thebarriertorotationisassociatedwiththedisruptionofthisresonance.InMOterminology,theorbitalwiththeC=O∗orbitalprovidesastabilizeddelocalizedorbital.ThenonplanarformleadstoisolationofthenitrogenunsharedpairfromtheC=Osystem.N:NCH3CH3ORORNCH3CH3C=O*C=Ob.Thedelocalizedformissomewhatmorepolarandispreferentiallystabilizedinsolution,whichisconsistentwiththehigherbarrierthatisobserved.c.Amideresonanceisreducedintheaziridineamidebecauseofthestrainassociatedwithsp2hybridizationatnitrogen.CNOPhCN+–OPhThebicycliccompoundcannotaligntheunsharednitrogenelectronpairwiththecarbonylgroupandthereforeislessstablethananormalamide.NO:1.5.a.Thesiteofprotonationshouldbeoxygen,sinceithasthehighestnegativechargedensity.4SolutionstoProblemsb.ThesiteofreactionofahardnucleophileshouldbeC(1),thecarbonylcarbon,asithasthemostpositivecharge.c.AsoftnucleophileshouldpreferthesitewiththehighestLUMOcoefficient.ThephenylgroupdecreasestheLUMOcoefficient,whereasanalkylgroupincreasesit.Reactionwouldbeanticipatedatthealkyl-substitutedcarbon.1.6.Thegrossdifferencesbetweenthebenzo[b]andbenzo[c]derivativespertaintoallthreeheteroatoms.Thebenzo[b]compoundsaremorestable,morearomatic,andlessreactivethanthebenzo[c]isomers.ThisisreflectedinbothHfandtheHOMO-LUMOgap.Alsothegreateruniformityofthebondordersinthebenzo[b]isomersindicatestheyaremorearomatic.Furthermorebenzenoidaromaticityislostinthebenzo[b]adducts,whereasitincreasesinthebenzo[c]adducts,andthisisreflectedintheTSenergyandH‡.TheorderofH‡isinaccordwiththeobservedreactivitytrendONHS.Sincethesedienesactaselectrondonorstowardthedienophile,theHOMOwouldbethefrontierorbital.TheHOMOenergyorder,whichisNHSO,doesnotaccordwiththeobservedreactivity.1.7.TheassumptionoftheC−Hbondenergyof104kcal/mol,whichbycoincidenceisthesameastheH−Hbondenergy,allowsthecalculationoftheenthalpyassociatedwiththecenterbond.Implicitinthisanalysisistheassumptionthatalloftheenergydifferenceresidesinthecentralbond,ratherthaninstrainadjustmentsbetweenthepropellanesandbicycloalkanes.LetBEcbethebondenergyofthecentralbond:H=2C−H−BEc−H−H=208−BEc−104=104−BEcBEc221 propellane=104−95=5BEc211 propellane=104−73=31BEc111 propellane=104−39=65Thisresultindicatesthatwhileruptureofthecenterbondin[2.2.1]propellaneisnearlyenergyneutral,thebondenergyincreaseswiththesmallerrings.Theunderlyingreasonisthatmuchmorestrainisreleasedbytheruptureofthe[2.2.1]propellanebondthaninthe[1.1.1]propellanebond.1.8.ThevariousHH2valuesallowassigningobservedHH2andHisomasinthechartbelow.Usingthestandardvalueof27.4kcal/molforacis-doublebondallowsthecalculationoftheheatsofhydrogenationandgivesavalueforthe“strain”associatedwitheachring