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NCSU CH 221 - 221cam8-L13-skeletal

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11Objectives©Dr. Kay SandbergPrevious lecturesThis lectureAlkene preparationsAlkene reactionsE1 mechanism1) dehydration of alcoholsE2 mechanism2) dehydrohalogenation of alkyl halides2Generic addition rxnSection 6.1© Kay Sandberg(reverse of _____________)Addition reactionReactions of alkenesA B+A B3HydrogenationSection 6.1© Kay Sandberg_______________Addition reactionReactions of alkenesHH+HHAlkene(___________)Alkane(__________)HBr+Br2Δ, hνBrHO2CO2+H2OAlkaneFree-radical____________alkyl halide___________4Unsaturated vs saturatedSection 6.1© Kay SandbergHH+HHAlkene(unsaturated)Alkane(saturated)Addition reactioncan undergoPolyunsaturated oils/fats – contain double bondsHydrogenated fats – fats whose double bonds have been hydrogenated to form only single bonds.Addition reaction: HydrogenationReactions of alkenes5Enthalpy changeSection 6.1© Kay SandbergHH+HH___thermicheat of hydrogenation+432 kJ/mol+602 kJ/mol-411 kJ/mol X 2-346 kJ/moltotal “breakage”energy ____ = +1034 kJ/moltotal “makeage”energy ____ = -1168 kJ/molAddition reaction: HydrogenationReactions of alkenesΔHo=-134 kJ/mol= 134 kJ/mol6Alkene stabilitiesCCRRRRSection 6.2© Kay SandbergHeats of hydrogenation give evidence for alkene stabilities.CCHHHRCCRHHRCCRRHHCCRRHRmonoditritetra≈CCHRHRE27Role of metal catalystSection 6.1© Kay SandbergAddition reaction: HydrogenationReactions of alkenesHH+HHPt, Pd, Ni or RhGorxn progressionw/catalystw/o catalystmetal cat.catalyst provides a________________H = 1HD = 2HD2= molecular deuterium H2= molecular hydrogen8Generic addition reactionSection 6.1© Kay Sandberg(reverse of elimination E1)Addition reactionReactions of alkenesA B+A B9E1 review© Kay SandbergSection 5.15CCH XCCHαβH OHCH2CH3XHOCH2CH3δ+δ+δ+δ+Weak baseE1 (elimination unimolecular)In absence ofstrong base(only solvent)HOCH2CH3Now a strong ___ΔNot a strong enough ____Step 1: _________ Step 2: _____________ Strong base + Δ = E210Addition reverse of E1“H-”© Kay SandbergReactions of alkenes: Addition of HXSection 6.4X H+ H-XX H+ H-XPrepartion of alkenes: Elimination of HX (E1)Section 5.14ΔGo= ΔHo-TΔSoΔGo= ΔHo-TΔSoX H+ H-XΔGo= ΔHo-TΔSoσ-e’sπ-e’sΔH is _____ in EΔS is _____ in E11ΔGo= ΔHo-TΔSoEnergy analysis of addition© Kay SandbergReactions of alkenes: Addition of HXSection 6.4H X+ HXGood:started out _, ended up _no longer bonded to _electron perspectiveelectron perspectivehalogen perspectivehalogen perspectivehalide ions: “stink” as Bronsted bases, but they are good nucleophilesBad:______ perspective – SM: 2 species; P: 1 speciesDoes anything “good” result? (i.e. lower energy)Does anything “bad” result? (i.e. higher energy)ΔHo= -54 kJ/molBroke _____er bonds & made _______er bondsLo T12Addition of HX© Kay SandbergReactions of alkenes: Addition of HXSection 6.4X H+ H-Xalkene hydrogen halide alkyl halideπ e-s313Step 1HX+Reactions of alkenes: Addition of HXSection 6.4H X+ HX+ H Xalkene_____ basic (π electrons)HX _____ acid(HCl, HBr, HI)Step 1______conjugateacid_______conjugatebasePotential Erxn progression14Step 2HX+© Kay Sandberg+ H XHX_________ additionδ-δ+δ-Reactions of alkenes: Addition of HXSection 6.4H X+ HXstep 1step 2Potential Erxn progression15Reactivity of HX© Kay SandbergReactions of alkenes: Addition of HXSection 6.4BrCH3CH2CH2CHCH2CH33-bromohexaneH3CH2CHHCH2CH3+ HBrcis-3-hexene-30oCHCl3HI >HBr >HCl >> HFReactivity of HXMostacidic,_____reactiveLeastacidic,_____reactiveΔGo= ΔHo-TΔSo16Markovnikov’s Rule© Kay SandbergXHRCHCH2HXRCHCH2RHHH+ HXReactions of alkenes: Addition of HXRegioselectivity of HX addition___________ Rule“Unto everyone that has more will be given”XHR2CCH2HXR2CCH2RRHH+ HXXHR2CCHRHXR2CCHRRRHR+ HX172 scenarios© Kay SandbergReactions of alkenes: Addition of HXMechanistic basis for Markovnikov’s RuleSection 6.6RHHHHX+RHHH+ H XRHHHX+HRHHHH X____ stable____ stable18Energy comparisonRHHHCC© Kay SandbergAlkene - Electrophilic Addition: HXSection 6.6C-C π e-: baseCRHHHCXHδ−δ+CHHRHCHXXHCHHRHCXHδ−δ+CRHHHCHX_o_oGo4192121Example21H Cl© Kay Sandberg_o21H Cl_oHClMOP_____ stable,____er formationClCl20Reactivity of alkenesRRRHCCRRRRCC© Kay SandbergAlkene - Electrophilic Addition: HXSection 6.6Reactivity of alkene (basicity of π e-)<<<Increasing Reactivity of alkeneHRHRCCRHHHCCHF << HCl < HBr <HIReactivity of HXIncreasing Reactivity of HX21Alkene electrostatics© Kay SandbergSection 6.6Reactivity of alkene (basicity of π e-)Increasing Reactivity of alkeneHHHHHHHH3CHCH3H3CHCH3CH3H3CHCH3CH3H3CH3Cnonemonoditri tetra22Problem© Kay SandbergDraw the MOP for the following:DCl-30oCMOPDCl-30oCMOPABH = 1H (protium)D = 2H (deuterium)same chemicalreactivity sinceboth are hydrogens(only difference is in rate)Unlike the protium isotope of hydrogen (symbol H),deuterium is NOTunderstood and must be shown.Use the X-tool on JME toolbar to input D.23Example© Kay SandbergSection 6.7Alkene - Electrophilic Addition: HXCCHHCHCH3H3CH0oHClCCHHCHH3CH3CHHClCCHHCHH3CH3CHHCl__oalkyl chloride(__%)24ExampleCCHHCHCH3H3CHHCl0oCl© Kay SandbergSection 6.7Alkene - Electrophilic Addition: HXCCHHCHH3CH3CHHCCHHCHH3CH3CHHCl_oalkyl chloride(__%)Evidence for _________formation._o_o525Rate comparisons© Kay SandbergSection 6.7Alkene - Electrophilic Addition: HXRates of ________ shift & _________ attack are similar.3oalkyl chloride(__%)Rearrangement: ____________ shiftEvidence for ____________formation.2oalkyl chloride(__%)vsCCHHCHH3CH3CHHClCCHHCHH3CH3CHHCl26Hydration© Kay SandbergSection 6.10Alkene - Electrophilic Addition:CCH OH+H OHSOOOOHHOHHSOOOOHOHHHpKa= -4.8pKa= -1.7Add the elements of water across the π bonddilute H2SO4Hydration27Proton “taxicab”Section 5.12SOOOOHHHOHwaterK>1What’s really in the flask!pKa~ -4.8pKa~ -1.7SOOOOH+With a lot of water (i.e., dilute), all of the sulfuric acid will bedeprotonated so that the “proton taxi cab” will toggle between_______ (the “proton picker upper”) and _____________ (the “proton dropper offer”) .OHHHpppOHHWhen the reagent isdilute acid or aqueous acid, you need to seewater and hydronium ion(or alcohol )28Step 1, NOT thisH3CCCH3COHHHHH+© Kay SandbergSection 6.10Alkene - Electrophilic Addition: HydrationCCH OH+H OHdilute H2SO4alkenes are _______δ-________phile bonds with ________phile.(Negative “grabs” positive, right?)29Step 1H3CCCH3COHHHHH+slow© Kay SandbergSection 6.10Alkene - Electrophilic Addition: HydrationCH3CCH3COHHHHH+alkenes are


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