CHE331-800 11.5 - Using the 5-2 and RS designations give...

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Unformatted text preview: Using the 5-2 and RS designations, give IUPAC names for the following alkenes. A/- I "" - ;\ BE$=€ZEI€(CE‘322,.. 1 $07000 i Ch c1 a rooPmOLéé‘ ' ‘ ‘ij * ’ B. " {no H @999 \ C==C “4 ii‘cm‘? E) 5 s) 4 mew 4 “Wm - 3 ‘- Chaptcr 7 9 Relative Stabilities of Alkenes 9 Generally, cls alkenes are less stable than trans alkenes because of steric hlnderance. ~ 0 Heat of Hydrogenation 9 The relatlve stabllltles of alkenes can be measured using the exothermic heats of hydrogenation. —aao\ a WWW Chapter 7 gm I) Heats of hydrogenatlon of three butene lsomers: ' m 1m“ ’ru‘ 2‘ w \‘u ,rntcn 2 CH6 p: (2 . n‘ H‘ ‘H "J" v" i 7- l _ . n1, Imp’ , 1 H mm ' ’ ,' \ _. , ll «in, l s M mm 1 ‘ “1 -I- All' 2 420 H mm“ : l AH" v. H‘J kll mm ‘ (‘HJt‘N/fll .(11 l. 0 Overall Relatlve Stabllities of Alkenes ID The greater the number of attached alkyl groups, the greater the alkene' e stability. Relall'rc Stalrl'litivx ofAlkrm's R RR \ C ==C :r« C . \ / R R R H R 'l‘etnlsubslituled 'l'riauhsllluted *— ' /' '\ ” / ‘ / \ . \ 1| H R H ll H u H u Disubslilulul Mnnosuheliluled l'mllbslituted Chapter 7 5 Cycloalkene Stability A A R R All of these exisW However, trans-cyclooctene has been isolated. L” /:< H H / , 1+ V Chapter 7 6 10/28/13 10/28/13 0 Synthesis of Alkenes via Elimination Reactions 0 Dehydrohalogenation ID Reactions by an E2 mechanism are most useful. B 1'1“ ..... W, H \_ n 3‘ " \ / ‘3— ’—-+” C==C + an + :x~~ * / \ \X 9 E2 reaction are favored by: ~k Secondary or tertiary alkyi halides * Alkoxide bases such as sodium ethoxide or potassium ten-butoxlde In high concentrations * Elevated temperatures (50°C or higher) 9 Bulky bases such as potassium ten-butoxide should be used for E2 reactions of primary alkyl halides. Chapter 7 e Zaitsev’ 5 Rule: Formation of the most substituted alkene is favored with a small base (OH', CHao', or nu n-). _ . CH3 “ /C”' ‘ W61 ’E’,’x""” [‘mx‘d” —" (‘11,(‘H=C\ 9 H "" " B -- 'liri V. //..,II ,t (“3; CH / 'h _t.' i B; a // (:l’.{‘('jl:{__(:: ~ “‘5 __ 2-‘\'lull|_\l-2-hulrm- CH cu: n ' ’ (f ‘ r / 1 ‘ . 4L—-Cli‘(‘lld('\ n---- u + in: TU . Z CH‘ 2-llromo~Z-nwihyllmmnr 2-Mt'lllyl-Lhuittne ¢ Zaitzev’ 8 Rule: when two different alkene products are possible In . an elimination, the most highly substituted alkene will be the d . Sub malor product. .. . .Cm . .. . .. . . CH: /7 (‘H CH 0' 4- CH CH Cl‘"CH (‘H C} "C/ -+- CH (‘H ‘/ ' “- 3 ' e‘ ' -‘| " CiizCHgUH " ‘ ' i‘ \ ‘ ' 1" :(\_‘ . Br C H. ( H. 2-h'lelhyl-2-hutcne Z-Melhyl- l -hutenc 7 (60%) (31%) «H1 3,11%)?hm51d) / a 1 ‘ *‘QO 1" @ C‘s bod—:CW WMM wam‘n‘uem: L of}an ii: SLYULL £11.56 0366’ *Om‘és QEtfg .on wnm'o 000W 09a my. wining “fl/UL “mu” fabié’i m get W 10/28/13 ID Klnetlc control of product formation: One of two products ls formed because Its free energy of activation is lower and therefore the rate of It form tlonls hlgh‘rg. .fioq W {)3 l .1 £1“ C «1:13 H i (:Hgvnzx‘ .e, L L (\w, H " in: H 5 Less stable tfansiimn slate resembles a d:substélutud CH ,fr—c’c'“ x H More stable lransnien stale resembles a lnsuhshluted alkene l css airfoilzd‘7ciiz + (‘lli(:ll._&lll . c: 14111.; i + (:1 m ; 27.‘Y".e"‘¥‘,.} 'f’mw V (:ll_‘(‘1vl:L'r,;1l;. + Vinny»: . 2:, I 2 bulcne 0 Formation of the least substituted alkene using a bulky base (an exception to Zaitsev’ 5 rule) ID Bulky bases such as potassium tert-butoxide have difficulty removing sterically hindered hydrogens and generally only react with more accessible hydrogens (e.g. primary hydrogens). CH. CH‘ ‘ . ‘ * («Ht ( H, r 1 ,, t . I‘ 75% . . _ ./ ' t” ‘l e/ ‘ (,H1 O + (.ihCle BI (CHWCOH-r (,,|i‘,(.l--l———(,\ + ( 3L, 'l._.(,\ ('sz CH} CH< (HA Z-MethyLZ-bulenc Z-MelhyH-bulene (27.5%) (72.5%) (more substituted) (less substituted) Chapter 7 10 T.Ql"3rbv+DX{cM EXQQWD’” @ WA l'rCULQ, i _ m ore SedbSHwOUO‘ 10/28/13 o The Stereochemistry of E2 Reactions: The Orientation of Groups In the Transition State I9 All four atoms Involved must be In the same plane: mum: Ii "*u_ .1 L- - ‘ fl \thf H (C it 5e (/0 Anti coplanar Syn coplanar transition state transition state / (preferred) (only with cerlnin rigid molecules) L I} In a cyclohexane ring the ellmlnatlng substituents must be m to be anti coplanar. '3 K“ 11 11 \. r\\ f ‘ tux/fl” V H :61] l): H \- /I-I H E \H —"; t‘! H (“i ~l Here the B-hydmgen and the A Newman projection formqu chlorine are both 231]". This shows that Ihc B hyd rugcn and allows an anti coplanar the chlorine arc anti co lunar 1] transition state. when they are both axial. IO Neomenthyl chloride and menthyl chloride give different elimination products because of this requirement down HFC wCHtcm HK‘C CHICHQ) “at! d CLOn CI Neomenthyl chloride Menthyl chloride I} In neomenthyl chloride, the chloride Is In the axial position in the most stable conformation $026+ 0mm Jm swash Mead i _ i-Muunem (78%) O (more stable nikenci u») lit—“(:le 5%; I. ll / WHICH»: H ,C ~_J..—-7‘;L\(‘/ H ’ *H' 9; li1(7><:)l-‘(WI(CH‘IZ Nuomenthyl chloride /'*~ . liothgim/flhyiirogem um ‘(lllil to thz: vb urim‘ in llii» thr mori‘ Sinhic 2~Menthene (22%) I'DIilhrmaliulL Elimination by path luv "€85 SHINE fllkflfle) Irme to lqi'n'nlhrmr: ivy path xin to lxnwmhmc. it 59. gimb‘a‘b‘ivenm Who to Ice ‘M + 12 r ‘\‘ . v.7,t " 'l / ' ' i, It \ 'ti‘x Cit/'H‘vau » whim ’w \ ‘7.) K ‘ 1 pr ll .‘ , i 6 ’€( \‘\\:A| 'v\l it WW 3 am am C077 mm,» .‘y "\(L- \ “‘{t‘\‘l(/ H l g \l 10/28/13 9 In menthyl chloride the molecule must first change to a less stable conformer to produce an axial chlorlde (slow). /“ """ "*CHCHm A ‘ ~~~~ \I ‘ ‘ H mLi-x 7.1m ( H} ,1 .H “th a 2 (WOW: ,5 /} T7 \ ~i/ \ >>>>>>> J 4 u ‘ ._ .. V n ‘ 3—3 1" let ~~~~~ H (..H(LH3)J Mcnlhyl chloride z-Mcnthenc (100%) (more Mable nmfarmmion) ixliminmimi iy out gxmsihlf l'm' tam umlkn'suzmun lwmtw ms indwgt-n is :mti in the lemma“; group. Mcntllyl chloride (less stable conformation) luliminaiion ix pmaihiv l'mm “fix «unlini‘zmxiz'mx hunuixr lhi~ git-sin lm‘lrtmuu n mm is: the vhlm‘inu 5;“? tum .Gorcmg m cenoli‘fim *0 (35* 5“ “'W‘Wm om 9% Wm Chapter 7 l3 What is’the major produot in each of the following elimination reactions? (“:53 M a M\8U\1nfiwfl’l CLCL—O A. H . , / r/Av/ W99 Q“ ' CH3CH20Na CH3CH20H ""Cl exifl/QD. is; wing was cam/ma insimd 00 ma, 2+ LOOUICI W mo mew. 10/28/13 9 Acid Catalyzed Dehydration of Alcohols l 1 HA \ / _ 7., (j =C + H ,0 l | hoax / \ v I) Elimination ls favored over substitution at higher temperatures. I) Typical acids used in dehydration are sulfuric and phosphorlc. I} Ease of dehydration: 3°> 2°> 1° T til H\ /H : l H —C—C—H /C=(.‘\ +1120 I I 180°C ['1 ()H H H Ethanol (a 1L alcohol) LITH.‘ (“j”) 20‘; H CH1_C_~0H Mg: llll Arms“; c I. H)” l 55 L CH;/ \(‘IL CHI ten-Bury! 2~hv‘lel_hylpropeno 1 5 alcohol (84%) o Mechanism for Dehydration of Secondary and Tertiary Alcohols: Anjjjmm I) Only a catalytlc amount of acid Is required since it is regenerated Wn the final step of the reaction. W _ I g 0 /\ . . -'— A l ‘ ’ H H rmw c— O~H >H'0 Pk— WVC‘ e Kit I i i 0 H H M W” 3’ B M O R ll CH 1 . + l7 i C + H3O mil’Q (76/ WW Chapler7 16 ...
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