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NCSU CH 221 - 221cam8-L10-skeletal

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11Lecture objectives©Dr. Kay SandbergLast lectureThis lecture’s objectivesSpectroscopy1) Alkene nomenclatureC-13 & proton NMR2) Alkene physical properties3) Alkene preparations2Spectra matchingClClClClClClIIIABCQDTTIIISQT3Starting material spectrum012PPMtripletdoubletsingletquartetseptet1H NMR of starting material©Dr. Kay SandbergBr2Δ,hν4MOP spectrum012PPM1H NMR of product (2-bromo-2,3,3-trimethylpentane)1234acdbba Br5Alkene nomenclatureCHAPTER 5: Alkenes - structure & preparationHydrocarbons containing C = C (double bonds)IUPACCCHHHHCCHHCH3H______common propylene_____ ethylene CCHHCH3CH3isobutylene ___________Section 5.1©Dr. Kay Sandbergalkenes are also called “_______” (oil-forming)alkane old-fashioned name “________”(“not enough affinity”)6Alkene nomenclature rulesAlkenes -nomenclature1) Find the longest, continuous chain containingthe double bond. (This is the parent chain.)ene‡The double bond takes precedence over alkyl & halide substituents.eneSection 5.12) Number the parent chain from the end closestto the double bond. 3) Use a locant to identify the firstC of the doublebond. (This locant immediately proceeds the parent name.)12345543214) Suffix is “ene” to indicate the presence of a =pentpent-1- -2-CnH2n©Dr. Kay Sandberg1-pentene 2-penteneold fashioned27Alkene precedence – alkyl & halideCl‡The double bond takes precedence over alkyl & halide substituents.Section 5.1hexeneAlkenes -nomenclature123456ab©Dr. Kay Sandberg1-6-chloro-3-ethyl-6-chloro-3-ethylhex-1-enenew fangleold fashionLocates 1stC of double bondLocant immediately precedesfunctional group for which itlocates.8Alkene precedence - hydroxyOH‡The double bond takes precedence over alkyl & halide substituents.Section 5.1Alkenes -nomenclature# from the end closer to the OH.Name:123456 7ahept-6-en©Dr. Kay Sandberg-3-ol6-methylnew fangleold fashionWhether old fashion or new fangle, drop “e” at the end of “ene” when next suffix begins with vowel(i.e., since “ol” for alcohol begins with the vowel “o”, drop last “e” of “ene” or “ane”.)6-methyl-6-hepten-3-ol‡Hydroxyl groups takeprecedence over double bonds.hept-6-en-3-olElm9Alkenyl group namesSection 5.1_____Alkenyl - common name_______________________©Dr. Kay SandbergH2CH2CCHCH2H2CCHH2CCCH310Alkenyl compoundsSection 5.1allylAlkenyl - common namevinylisopropenylmethylene©Dr. Kay SandbergH2COH3-vinylcyclohexanolH2CCHCH2H2CCHH2CCCH3OH3-allylcyclohexanolOH3-isopropenylcyclohexanolOH3-methylenecyclohexanolcyclohexanol11Cycloalkene numberingBr Br BrSection 5.1Cycloalkenes - nomenclaturecyclohexene12Cycloalkene rulesSection 5.1Cycloalkenes - nomenclatureBr Br Br©Dr. Kay SandbergDouble bond has precedence over halides & alkyl groupsand is understood to be between C1=C2You have to locate everything on chains!!Dogwood313StereoisomersName this alkene?-?-same side of double bond 6-methylhept-3-eneopposite sides of double bond 6-methylhept-3-ene©Dr. Kay Sandberg_____________Different energies, bp’s, etc.14HHH3CCH3HH3CHCH3cis/trans alkenesHHHCH2CH3CH3HHCH3Isomerism in alkenes: (C4H8)but-1-eneSection 5.32-methylpropenebut-2-ene but-2-eneAcross the double bond Same side of the double bond©Dr. Kay Sandberg15Isomeric relationshipsIsomeric relationship: (C4H8)Section 5.3HHH3CCH3HH3CHCH32-buteneHHHCH2CH3CH3HHCH31-butene2-methylpropene2-butenetrans-cis-abcd©Dr. Kay Sandberg16Vinylic substituentsIsomeric relationship: (C4H8)Section 5.3HHH3CCH3HH3CHCH3but-2-eneHHHCH2CH3CH3HHCH3but-1-ene2-methylpropenebut-2-eneIdentical vinylic substituents on same C - ______________CCCC©Dr. Kay SandbergAdjective meaning “bonded to sp2C of DB.”17How do you assign configurations for these two?HHH3CCH3Section 5.4HClBrFFClBrH1-bromo-1-chloro-2-fluoroethene1-bromo-1-chloro-2-fluoroethene©Dr. Kay Sandberg18E-Z notationE-ZnotationSection 5.4HClBrFFClBrH___1-bromo-1-chloro-2-fluoroetheneentgegen(Ger. “opposite”)1-bromo-1-chloro-2-fluoroethenezusammen(Ger. “together”)_____configuration©Dr. Kay Sandberg419Example 1Section 5.4CH3ClBrCH2CH3Higher rankLower rank___-1-bromo-1-chloro-2-methylbut-1-eneE-Znotationbased on rank (atomic #) @ 1st point of difference©Dr. Kay Sandberg20Example 2___-4-bromo-4-chloro-3-isopropylbut-3-en-1-olHigher rankLower rankCH(CH3)2ClBrCH2CH2OHSection 5.4E-Znotation___-4-bromo-4-chloro-3-(1-methylethyl)but-3-en-1-ol©Dr. Kay SandbergE or Z configuration?21Example 3(_)-3-bromo-2-tert-butyl-3-chloroprop-2-en-1-olC(CH3)3BrClCH2OHSection 5.4E-Znotation©Dr. Kay SandbergE or Z configuration?based on rank (atomic #) @ 1st point of differenceBirch:22BrDiene nomenclatureSection 5.3© Dr. Kay Sandberg23Bonding in alkenesCCHHHHEthene (C2H4)110 pm134 pm117o121oCCHHHHHHEthane (C2H6)153 pm368 kJ/mol___ kJ/molπ bond is _______than a σ bond.Section 5.2111 pmsp3sp2©Dr. Kay SandbergDB = 1 σ + 1 π24Bonding in alkenesCCHHHHXZsp2Section 9.3© Kay SandbergYZpypyrotate 90orotate 90oCCHHHHσ bondhttp://www.youtube.com/watch?v=BodXwAYeTfM525Electrostatic potential map of etheneSection 5.2©Dr. Kay Sandberg_________26CCH3HCCHH3CHCH3Interconversion of isomersSection 5.3©Dr. Kay SandbergCCH3HHCCH3CHHHCH3HCH3CHH14 kJ/molInterconversion of conformations of butaneanti conformation gauche conformation_____ kJ/molvs(E) configurationInterconversion of configurationsof 2-buteneCH3CH(Z) configuration______________________________27E/Z conversionH3CHCH3HSection 5.3restricted internal rotationH3CHCH3HCH3HCH3H©Dr. Kay Sandberg250 kJ/molCCH3HCCHH3CHCH3CH3CH(E) configuration (Z) configuration______________250 kJ/mol28Biochemical intersectionSection 5.3©Dr. Kay SandbergOHHOhνretinalOh, I see!aldehydecis-trans isomerization1234529Hybridization & electronegativitysp2hybrid orbitals: __% scharacterThe mores character, the _______ theelectron probability of being near nucleus Physical Properties of alkenesSection 5.5sp3hybrid orbitals: __% scharactersp2hybrid C is _____electronegative than sp3 hybrid C ©Dr. Kay Sandbergsp hybrid orbitals: __% scharactersp hybrid C is the _____ electronegative type of C the ______ the energythe ______ electronegative the atom 30CCRRHHRHydrocarbon aciditiesWhich was easiest to deprotonate(i.e., the most extensive deprotonation)?sp2hybrid orbitals: 33% scharacterSection 5.5sp3hybrid orbitals: 25% scharactersp hybrid orbitals: 50% scharacterCCRRHRCCRRHHHRCCHRBaseBaseBaseCCRCCRRRsp ____ stablesp3___ stable©Dr. Kay SandbergHydrocarbon acidities631Carbanion stabilitiespKa~__sp2hybrid orbitals: 33%


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