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Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,5.1Alkene Nomenclature,characterized by molecular formula CnH2n,have a C=C double bond,said to be unsaturated“or“olefins,Chapter 5Structure and Preparation of Alkenes:Elimination Reactions,Chapter 5;Alkanes and Elimination Reactions,Nomenclature,Geometric Isomers,Cis,/trans and E/Z,Priority Rules,Physical Properties,Alkene,Stability,Elimination Reactions,E1 and E2 Mechanisms,:H and:R shifts,Dehydrohalogenation,Reactions,1)Find the longest continuous chain that includes the double bond.,2)Replace the-,ane,ending of the unbranched alkane having the same number of carbons by-,ene,.,3)Number the chain in the direction that gives the lowest number to the doubly bonded carbon.,H,2,C,CHCH,2,CH,3,1-Butene,Alkene Nomenclature,4)If a substituent is present,identify its position by number.The double bond takes precedence over alkyl groups and halogens when the chain is numbered.,The compound shown above is4-bromo-3-methyl-1-butene.,H,2,C,CHCHCH,2,Br,CH,3,Alkene Nomenclature,4)If a substituent is present,identify its position by number.,Hydroxyl groups take precedence over the double bond when the chain is numbered.,The compound shown above is2-methyl-3-buten-1-ol.,H,2,C,CHCHCH,2,OH,CH,3,Alkene Nomenclature,Alkene Nomenclature,If more than one double bond is present;name as a,diene,or,triene,.Use numbers to indicate multiple bond positions.,Cycloalkene Nomenclature,1)Replace the-,ane,ending of the cycloalkane having the same number of carbons by-,ene,.,Cyclohexene,1)Replace the-,ane,ending of the cycloalkane having the same number of carbons by-,ene,.,2)Number,through,the double bond in thedirection that gives the lower number to the first-appearing substituent.,6-Ethyl-1-methylcyclohexene,CH,3,CH,2,CH,3,Cycloalkene Nomenclature,1,2,3,4,5,6,Planar,Restricted C-C Bond Rotation,Structure of Ethylene,Isomers,Constitutional isomers,Stereoisomers,different atom connectivity,same atom connnectivity;different arrangementof atoms in space,Requirements for Geometric Isomers(Type of Stereoisomer),Restricted Bond Rotation,Cycloalkane,Multiple Bond,Two Different Carbon Atoms that Have Two Different,Substituents,Attached to Them,2-Methylpropene,1-Butene,cis-,2-Butene,C,C,H,H,H,CH,2,CH,3,H,CH,3,C,C,H,3,C,H,C,C,H,H,H,3,C,H,3,C,Constitutional Isomers,of C,4,H,8,cis-,2-Butene,trans-,2-Butene,H,3,C,C,C,CH,3,H,H,H,CH,3,C,C,H,3,C,H,Stereoisomers,of C,4,H,8,Also known as Geometric isomers,cis/trans isomers,or,E/Z isomers,E,Z nomenclature is used when cis/trans ranking is ambiguous,What is needed:1),systematic body of rules for ranking substituents,2),new set of stereochemical symbols otherthan cis and trans,C,C,H,F,Cl,Br,C,C,E,:higher ranked substituents on,opposite,sides,Z,:higher ranked substituents on,same,side,Entgegen,higher,higher,lower,lower,C,C,Zusammen,lower,higher,lower,higher,The E-Z Notational System,(1)Higher atomic number outranks lower atomic number,Br FCl H,(,Z,)-1-Bromo-2-chloro-1-fluoroethene,higher,lower,Br,F,Cl,H,higher,lower,C,C,Table 5.1 CIP Rules,(2)When two atoms are identical,compare the atoms attached to them on the basis of their atomic numbers.Precedence is established at the,first point of difference,.,C,H,2,C,H,3,outranks,C,H,3,C,(,C,H,H),Table 5.1 CIP Rules,C,(H,H,H),(3)Work outward from the point of attachment,comparing all the atoms attached to a particular atom before proceeding furtheralong the chain.,C,H(,C,H,3,),2,outranks,C,H,2,C,H,2,OH,C,(,C,C,H),C,(,C,H,H),Table 5.1 CIP Rules,(4)Evaluate substituents one by one.Dont add atomic numbers within groups.,C,H,2,O,H outranks,C,(CH,3,),3,C,(,O,H,H),C,(C,C,C),Table 5.1 CIP Rules,(5)An atom that is multiply bonded to another atom is considered to be replicated as a substituent on that atom.,C,H=,O,outranks,C,H,2,O,H,C,(,O,O,H),C,(,O,H,H),Table 5.1 CIP Rules,Alkene Polarity and Boiling Point,Dipoles cancel;,Trans isomer nonpolar,Lower boiling pt,Dipoles reinforce;,Cis isomer polar,Higher boiling pt,Double bonds are classified according tothe number of carbons attached to them.,H,C,C,R,H,H,monosubstituted,R,C,C,R,H,H,disubstituted,H,C,C,R,H,R,disubstituted,H,C,C,R,H,R,disubstituted,Double bonds are classified according tothe number of carbons attached to them.,R,C,C,R,H,R,trisubstituted,R,C,C,R,R,R,tetrasubstituted,In general;the more substituted the alkene is,the more stable it is.,Electronic(larger effect),disubstituted alkenes are more stable than monosubstituted alkenes,Steric(smaller effect),For disubstituted alkenes;,trans,alkenes are more stable than,cis,alkenes,Substituent Effects on Alkene,Stability,+6O,2,4CO,2,+8H,2,O,2707 kJ/mol,2717 kJ/mol,2710 kJ/mol,Figure 5.4,Heats of combustion of C,4,H,8,isomers.,cis,-2-butene,trans,-2-butene,van der Waals straindue to crowding ofcis-methyl groups,Figure 5.5 cis and trans-2-Butene,Give the structure or make a molecular model of the most stable C,6,H,12,alkene.,C,C,H,3,C,H,3,C,CH,3,CH,3,Problem 5.8,
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