CHE 331-800 11.12 - 63 800 Le fie Vfé Problem WIN/4 BMW...

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Unformatted text preview: \\ 63/ / 800 Le fie Vfé; Problem: WIN/4 BMW synthesize M from H_CEC_H H H Retrosynthesis: Synthesis: NI}z _fi_ - NNHL J H—CEC*9\ L—aGQEC—a ,4?” 01—0309 10/28/13 18 Chapter 8 Alkenes and Alkynes ll: Addition Reactions \ / C=C / \ Alkene Overview of some addition reactions ,mqwufi' WW”? _ | I H X H—C—C—X H—Oll HA (cum Chapter 8 Alkyl halide (Sections 8.2. 8.3. and 10.9) Alkyl hydrogen sulfate (Section 8.4) Alcohol (Section 8.5) [)ihaloalkane (Sections 8.1181?) 11/11/13 0 Introduction: Additions to Alkenes addition I I / .‘ +A-B / \ ; I} Generally the reaction is exothermic because one 1: and one a bond are converted to two 0 bonds A—C—(f— 11/11/13 B TVU “3 5 Y, Li W) +73 add WW? I [in 51/524711 \ < / + --‘Y-—-) -— .—_ — a ‘ /C(=jc\ my) O1 41 ,. s i 1 xj/Y Whom! (Thom! -—> 2(rlmnds Bonds broken Bonds formed ChapterS 3 Mechanism occurs in two steps: A ITl ~ \ / Stow / .._ 2X21}. + C=C -—-> ----C——C+ +=X= no / \ l \ .- Electrophile Nucleophilc C C21 “EC (1130“ H H =§é= | / .._ | l —-C—c+ + —-+ --C--C- | \ i i Electrophile Nucleophile Chapters *NU M 3169 1 about LOiLQi/k flOf )W 161/!” The reaction has a highly endergonlc first step (rate determining) and a highly exergonic second step. (D- Transttion state 1 , Transition state 2 Carbocatlon xt)‘ 1" Intermediate H i/ Step 2 0 Addition of Hydrogen Halides to Alkenes: \ Markovnikov’ s Rule (C flejtilfbnoiu \ afil’V/LG. \/ CH1=CHCH3 + HBr "—9 CHfifHCH3 (little BrCHZCHZCH3) Br 2-Bromopropane l-Bromopropane -) Markovnikov' 5 Rule: Addition of HX to an alkene proceeds so that the hydrogen atom adds to the carbon of the alkene that has the greater number of hydrogen atoms. Carbon atom A CH3=CHCH3 —> CHE—CHCHJ with the z ? | i greater ” Br number of : 2 Markovnikov addition hydrogen atoms [1 Br product Chapter 8 11/11/13 11/11/13 0 Theoretical Explanation of Markovnikov' 3 Rule ID The product with the more stable carbocation intermediate predominates. ID The most stable carbocation is formed fastest because it has a lower AGt cripngéiig'i» CHjCHzCHIBr 1° l-llronmprupane H" (little formed) r CH3CH=CHl Sm, CHXCHCH3 CHXCITHCH.’ Br 2° Z-Brumopropane (main product) 1 Step I i ' Step 2 ‘ Chapter 8 7 *The more stable carbocation is formed fastest because it has a lower DGi: Br a {i , _ ; 1 Of This transition ‘ r, ‘ (/H-JgH: CH;Z istate resembles ‘ ,’ 8:.“ + ;a 10 carbocation. _ ,’ ; \CHJCHZCH2 ' - I m. g «- .. .. * - . ,’ o" :5 \‘:-.}.:”' “x “"5 “ammo” xl' i:i1;.<_:ii=t1u, \ state resembles I x . a V t - + ‘ ‘12. , 979931139] CH30HCI13 I + Br A0112“) AGi ( Pi \gHucHZCHZBr u.-.- CirIBCHRrCHa £1 , W V; (ii—L“erer ~; “A ,7 W 6 2C HANG}??- . r > x” n V m “MM” “u” “ '~< r . 11/11/13 I) Addition of HBr to 2-methylpropene gives only lert-butyl bromide. CI‘H; CH1 \ r . - H‘C-vC—CH, > C. CH‘ n > H‘C (3—(2HI Md“. » \ - rm“ / \ — I. v - I ~ product n~ In: CH} \w, =ll5'r1 ; m; 3° Carbocalion terI-lhltyl bromide {more slalllt‘ mrhucmium CH1 CH1 CH1 H ("—Cl‘———Cll ‘/ > n c 6H V > H C on (‘11 Ii - “‘“e 3 u v 2 \ .1 I 2 ‘ l ’ ‘ ' 3 "r. formed w. H ll—if'ri .- l” Carbocation lsohmyl bromide (it‘s): stable mrlmmxiam) I) Regigfiglggjiyg Reaction: When a reaction that can potentially yield two or more constitutional isomers actually produces only one or a predominance of one isomer. Chapter 8 9 O Stereochemistry of the Ionic Addition to an Alkene QAddition of HBr to 1-butene yields a racemic mixture. CH3CH2CHICH2 + HBr —> CH3CH2$HCH3 Br (R,S)-2-br0mobutane Mechanism: Chapter 8 10 Draw the structure of the major product of each reaction. A. \/\/\ + HBr —> Chapter 8 ll 0 Addition of Sulfuric Acid to Alkenes I) Addition 0! concentrated sulfuric acid to alkenes leads to alkyl hydrogen sulfates. The addition follows Markovnikov' s rule. H H H \ \ | C=CH,-—~+ C—CHt—H ——) H‘C—C—CH; / ‘ / 2 ‘ | ‘ “it 13.. “1 \\ _ .. ‘ zosoJH [I w 980]" \-~-- = 950,11 2° Carbocalion lsupropyl hydrogen (more stable carbocation) sulfate ¢ The sulfate can be hydrolyzed by heating with water * The net result ls Markovnikov addition of water to an alkene ‘ ‘ ‘ cold ‘ a ‘ 11.0. hum ‘ ‘ ‘ ‘ (,H1( H=(,H3 I—lk—’ (H1(,H(.H1‘—> (,H1(.H( H1 + H350; I). l I ()Smll on Chapter 8 11/11/13 ...
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