Organic Chemistry I
Organic Chemistry I CHEM 2010
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This 24 page Class Notes was uploaded by Columbus Kerluke on Sunday October 11, 2015. The Class Notes belongs to CHEM 2010 at East Tennessee State University taught by Yu-Lin Jiang in Fall. Since its upload, it has received 47 views. For similar materials see /class/221419/chem-2010-east-tennessee-state-university in Chemistry at East Tennessee State University.
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Date Created: 10/11/15
7 Alkenesz Reactions and Synthesis Based on McMurry s Organic Chemistry 6th edition Diverse Reactions of Alkenes n Alkenes react with many electrophiles to give useful products by addition often through special reagents I alcohols add HOH I alkanes add HH I halohydrins add HOX I dihalides add XX I halides add HX I diols add HOOH I cyclopropanes add CHZ H OH H H 40C 7 X AIBOhOl Alkane 40C v HJv Halohydrin 12Diol X X C C K fa 00 Carbonyl 12D1hallde compound H C 70C 7CC Halide Cyclopropane 2004 Thomson Brookleole 71 Preparation of Alkenesz A Preview of Elimination Reactions Addition 020 X Y C Ci Elimination 2004 Thomson BrooksCole A Preview of Elimination Reactions El Alkenes are commonly made by elimination of HX from alkyl halide dehydrohalogenation using heat and KOH H Br H KOH CH3CH20H a I KBI H20 H H H Bromocyclohexane Cyclohexene 81 Thomson Brooks Cole A Preview of Elimination Reactions n elimination of HOH from an alcohol dehydration requires strong acids sulfuric acid 50 OC CH3 OH H2804 H20 THF 50 C CH3 H20 lMethylcyclohexanol lMethylcyclohexene 91 O i Tetrahydrofuran THF a common solvent Thomson Brooks Cole Prob 72 How many alkene products from dehydration CH CH3CH2CHZCH2CH3 3Methyl3hexanol CH3 2004 Thomson BrooksCole Solution 72 Addition of Halogens to Alkenes Bromine and chlorine add to alkenes to give 12dihaldes an industrially important process I F2 is too reactive and 12 too unreactive El Cl2 reacts as Cl Clquot Br2 is similar H H C1 Cl CC c12 gt H C C H Ethylene 12Dichloroethane Ethylene dichloride 2004 Thomson BrooksCole 9 Addition of BIZ to Cyclopentene n Addition is exclusively trans stereospecific HART Bra Br gt HQH Cyclopentene Br H trans12Dibromo cyclopentane Sole product 2004 Thomson BrooksCole cis12Dibromo cyclopentane Not formed 10 Mechanism of Bromine Addition El Br adds to an alkene producing a cyclic cation a bromonium ion in which bromine shares charge with carbon Tr Br H C H B Br 5 CC h uC Cw H 11 CC Irr H11 I le Hint NIH H H Hquot H H H Br a Him I llle 11 H H Mechanism of Bromine Addition I Since the Br blocks one face one must get anti trans addition Bra Br 2HH C n aquot i H Huwquot quotquot1qu 39 H H HZ Br E Br 12 Addition of BIZ to Cyclopentene Top side open to attack Bri39 Q HA3 Br gr 2BI 13139 H Bottom side shielded from attack Cyclopentene Bromonium ion trans12Dibromo intermediate cyclopentane 13 Top side open to attack r Q kBrBr Br H U Bottom side shielded from attaci Cyclopentene Bromonium ion trans12Dibromo intermediate cyclopentane 2004 Thomson Brookslcnle The Reality of Bromonium Ions n Bromonium were postulated more than 60 years ago to expain the stereochemical course of the addition to give the transdibromidefrom a cyclic alkene El George Olah Nobel Prize 1994 showed that bromonium ions are stable in liquid SO2 with SbF5 and can be studied directly by nuclear magnetic resonance spectroscopy H30 Br Br H30 r I SbF5 CC SbFe39 CH3 Liquid 802 H304 jiH3 I H CH3 H SbF5 Bromonium ion stable in 802 solution 15 Thomson Brooks Cole 73 Halohydrin Formation I This is formally the addition of HOX to an alkene with CH as the electrophile to give a 12halo alcohol called a halohydrin El The actual reagent is the dihalogen Br2 or Cl2 with water in an organic solvent X X2 A C C C H2O V HO HX An alkene A halohydrin 16 Mechanism of Formation of a Bromohydrin H IEXE H30 H Reaction af ne alkene with B132 1 yields a br mumium inn intermediate Br 3 6quot C Br 17 Mechanism of Formation of a Bromohydrin Water acts as a nuclenphile using a lune pair 0139 Electrans ta open the hmmmlium inn ring and farm a band 150 carbon Since oxygen dnnatea ita electrons in this step it now has the pusitive charge 314 17 V C JCK Bquot H r 7 CH3 1130 K3 H Qfla Br JCHB 9H quot 1 L n Hag i H 3 H quot 18 Mechanism of Formation of a Bromohydrm Br CH3 H J a of H C Cam H 3 V G a H w Loas of a pmttm H 39um 013an then gives Hammad the neutral 1 hmmohydrin additiun product iiCHIS t H CCquot 30 H1 Brnmm hutanul A hmnmhydrin Reaction of the alkene with Br2 yields a bmmonjum ion inbemediate Water acts as a nucleophile using a lone pair of electrons to open the bromonium ion ring and form a bond to carbon Since oxygen donates its electrons in this step it now has the positive charge Loss of a proton HI from oxygen then gives H30 and the neutral bromohydrin addition product 2004 Thomson BrooksCole H x C JrC 3 Br T 8 V H30 H Br 2 x C B H CHa H30 xx 9H2 Br CH3 QH C C 1316 QOLH a 6H2 H J Bquot CH3 0 C39I H H 0 Hquot quot H30 0H 3BI39Dmm2butnnol A bmmohydrin 20 An Alternative to Bromine n Bromine is a difficult reagent to use for this reaction I NBromosuccinimide NBS produces bromine in organic solvents and is a safer source 0 OH N Br N BS I CH CH2 CH CH2 Br O 0 HQOJ39CHgsCiCHg DMSO 0 Styrene 2Bromo 1phenylethanoili 76 2004 Thomson BrooksCole 21 74 Addition of Water to Alkenes Hydration n Hydration of an alkene is the addition of H OH to to give an alcohol El Acid catalysts are used in high temperature industrial processes ethylene is converted to ethanol H H C H20 11313233352113781 H H Ethanol Ethylene 22 2004 Thomson BrooksICole Reaction of an alkene with acid HA yields a carbonation intermadiate Water nuts as a nuclanph e a lane pair 0139 electrons on nxygen to farm a band tn carbon The nxygem 3mm having dnnated electmna is now trivalent and has the positive charge H C H n quota 3 x H A C i 390 H30 H EMamylpmpena l qu v H C G H A f I Eat yf ff Ht H 05 H HgG C G H HHC H 23