AlkenesStructureandReactivity：6烯的结构和反应性

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1、CH6:AlkenesStructureandReactivityReneeY.BeckerCHM2210ValenciaCommunityCollege2Alkene-HydrocarbonWithCarbon-CarbonDoubleBondAlsocalledanolefinbutalkeneisbetterIncludesmanynaturallyoccurringmaterialsFlavors,fragrances,vitamins3WhythisChapter?C-Cdoublebondsarepresentinmostorganicandbiologicalmolecules

2、ToexamineconsequencesofalkenestereoisomerismTofocusongeneralalkenereaction:electrophilicaddition4IndustrialPreparationandUseofAlkenesEthyleneandpropylenearethemostimportantorganicchemicalsproduced5NamingofAlkenesNametheparenthydrocarbonNumbercarbonsinchainsothatdoublebondcarbonshavelowestpossiblenu

3、mbersRingshave“cyclo”prefixIf2doublebonds–diene,If3doublebonds–triene……..678ManyAlkenesAreKnownbyCommonNames9Nameme10Drawme2,3,5-trimethyl-1,3-hexadiene3,3-diethyl-1-pentene4-sec-butyl-3,5-dimethyl-2,5-heptadiene3,3-dimethylcyclopentene3,6-dimethyl-3-octene11Cis-TransIsomerisminAlkenesCarbonatomsin

4、adoublebondaresp2-hybridizedThreeequivalentorbitalsat120ºseparationinplaneFourthorbitalisatomicporbitalCombinationofelectronsintwosp2orbitalsoftwoatomsformsbondbetweenthemAdditiveinteractionofporbitalscreatesabondingorbitalSubtractiveinteractioncreatesaanti-bondingorbital12Cis-TransIsomerisminAl

5、kenesOccupiedorbitalpreventsrotationabout-bondRotationpreventedbybond-highbarrier,about268kJ/moleinethylene13RotationofBondIsProhibitiveThispreventsrotationaboutacarbon-carbondoublebond(unlikeacarbon-carbonsinglebond).Createspossiblealternativestructures14Thepresenceofacarbon-carbondoublebondca

6、ncreatetwopossiblestructurescisisomer-twosimilargroupsonsamesideofthedoublebondtransisomer-similargroupsonoppositesidesEachcarbonmusthavetwodifferentgroupsfortheseisomerstooccur15Cis,TransIsomersRequireThatEndGroupsMustDifferinPairs180°rotationsuperposesBottompaircannotbesuperposedwithoutbreakingC=

7、C16SequenceRules:TheE,ZDesignationNeithercompoundisclearly“cis”or“trans”SubstituentsonC1aredifferentthanthoseonC2Weneedtodefine“similarity”inaprecisewaytodistinguishthetwostereoisomersCis,transnomenclatureo