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September 26 - October 3 - agitate#6 err See-Weft w eta/62m...

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Unformatted text preview: agitate #6 err, See-Weft. w eta/62m 3} moat Free radical halogenation Tim 4) Steam +5”; __ .4. o (9/ wt; eefie’é-auog, We can use the chtorination of methane to learn about some of the things we consider when we study a chemical reaction. It takes places in the gas phase. so we do not need to consider solvent effects. H H s in; (aim) ; C “tiff 21;” H / $9? + 8/52) H. /C\& e .zg‘gwe /€t.' ’fifb‘ fizz/take mega/RU Weaken (if—Cf met (5:; e. 2.42 fzJ‘ coszvmeot "Ee— CHE-t zfimct ($5 = 435 /fiJ/w,e€ « Jam/wt, shaman”? not/{,‘gsvcwedm/m) “as E NEOTH ER M1 C ‘1. Chlorination of methane is a radica hain reaction. Ail chain reactions have three types of steps: 1. initiation mm wfig 6,01% We. Wm 9L 1 e" ‘3 f“) ‘ 51:26:; afield (La/E ) (a e c a <2, Aer/“L otdofl. (2 Jul 4:3“: éwtmmwtfioig 2. propagation (em/chat» 2 6mm: wedge; “sfi’fi 5 ) if W H SEE: 4.31.12:- (,5) /C'<7/3 + WCH) act-:3 + kph/Em H gift“ 9° “930”; Am — Maia E ’ ate/T’mmewc' XL G" 1‘: BE _ = 435‘k3' «P f 0"“ M _ C H m *3 if” M =- Mia/wt A. e, o I p (A a ' e a g! WehaniSMzfi) Hjc° ‘1" 3996"” W HBCMC/{i 4— “(:69 ( ckftw ' N O" ‘ : ,5 a 6 ? h/LQCLC. Lei—14., b6 Qéwtzgmecacfi539’gg (BE-b 2'4ka LEE: 343%.?" AH;- FIG? £6 at, emiméjef “‘“ wt W Notice that adding the two propagation steps in a radicaf haiogenation reaction gives us the overall reaction: 0 7’ 13mm 0 a o e , _ 23%,,“ + we 0 #23 of? «in H 06’, 6mm H H ' A H :2 m- 1 04. its“ EXO‘TME RMEC Mechanism of methane chlorination, continued 3. termination steps H M i i-ijce/E-QGE‘; ms— “fig—4’2: AH: #349 5:6, H e {Semen/62 oycmecL 12-24, «Si—cf: Mt: ‘l’Se—v 19w jam/“,cmcwfiaflL/Law coca/Ce mmo’tt/Ga). J H3 c sci—{3 __..5_ H CWCH LXI—1m “368”{T 3 3 W 14455 no C0 we we gag/i. «CE: W game: «m = ~— m In 6 14456 Maire: Bea/cat {Mumwfiw «:45 exorr—reR/v’ilc I Using bond dissociation energies (BDE) to predict the enthaEpy change for the reaction: OHgtgj -i- 0&3.) "we- CH3 Cffi) + arc/EC?) AH m £33 “'- 23!? E" . . f2 x14. Acacia-£326 "‘ “Md; m (Sat: "Vb “Gama _. 7 eat—W, We: MW mat/er 1.: {4(435)+242J -— [3(435‘)+349+ 4317} k3“ 2-..- -—--- 703 M zucmc/fiéflw Alternative mechanisms have been roposed, b involve steps that are energeticain less favorabie. The pathway we just investigated is the lower energy pathway and thus is favored. Remember: a mechanism cannot be conclusively proven... only supported by experimental evidence. (A mechanism may be disproven, though.) Energy diagrams for muitistep reactions 5% Quarter 73L:- if] {a 3: . M (if 6% I T3 7:5: H; - . H H / ‘21:}! H fififfijmw / £393 *‘ “(5% 6‘72] H ,5 {'mmwunflg I __ energy reaction coordinate k9fo (<2) ’0; “Fig 2 eTfs ic/s fife, sxfimr} /La}$-oteimmvulmj rs‘i'jJS. @gemfle, fie. afiwo'tWLe/b 1758, W’fivLe. xch/L/OL «fine/afgdmacb & Mot L,th Me, 34% Adam {ML fie, fimefiflwg flood/dome Clack/0mm (go) \S’MW ~0Jg-c'08 . Haiogenation of higher atkanes and selectivity in chemical reactions Consider the possible products that can form on reaction of propane with chlorine. (HCl is also a product, but not shown here.) , , ted/moo fifo‘ZI/an/‘tlewfih (“kW/{Law CH30H20H3 + C]; —---> CH20I0H20H3 40% Z eggfowse/ge CH3Ct-ECICH3 60% j a we, Mafi- /z.e mofiw prof/13f 0: Why does one product form in preference to the other? Statistically. we should get a different outcome: first r424 [ H 'fltme me 6 H Met, 5?, (Seems/04, H Wig-H iwfflaécm. 511;;th fimeoLc‘thar-i/u.f H . .1 H__ fiJLWCtAa/fia es 6.: 2 .m 3: 7 fat, - Relative reactNIty: ) 1— cfifofico—ffi e, {To 2— C’fifoficofr‘wrv We.) _ C15 752 ME rowed, 25' Z A Selectivity in a chemicai reaction aiways arises from a difference in rates. flat/ts. v C’ilfi'me/CVW First consider the reaction mechanism for the retevant propagation step fort e formation of the first product, CHECICHZCHl 30:23” + NW Mfi+ HOE/'AHz—«Zlkf H .la/LMLde/e M N-ofe : 775m, foo/fa, cflif: ‘rI/b ~8>co7t1mmo rim/o Meet, “Eco CH4. EMULoT’l/chmoj fiim m i Now consider the reaction mechanism for the relevant propagation step for the formation of the other product, um s CH3CHCICH3, £18,; oat-{5 t. it a “u ' 56/60 + A -—->* /\ + We A“ “34th W Zfiflaett‘m/K WE/ mete, exo’ffimmo} : Zaflaou‘cm/Emjtfl 133M 5 1° I Ex WWW (Wit) Riots ‘3 X 402; (Rmatfm seesaw) (it 10H) fimofi Ame/Wag 2‘24 150 m e. 60 m at; 4o 2/ 1 @ Chlorination of higher alkanes: hydrogen reactivity and BDE gee/Ema adwflba fifa&[email protected]% Mfg/g Removal of a tertiary hydrogen by homolytic cleavage: (Rig/e ma‘flvaovgfi _ 14/07: 5 Z agwigafim OLA/6 é’C’CLLkWJao—wt/ Z’mewfiéw ' (335) canal/"few, vb ’ 33) E f ‘2" Jéfa‘atifieci A - (I Wfii/gevo 114/ H /a W a. . 3?.I‘Lckc’io‘acVE Removal of a secondary hydrogen by homolytic cleavage: /1§H W )i A 39 I? H "l 2," .WWE/ Removal of a primary hydrogen by homolytic cleavage: flf/«Ngg E a“ 440 13¢<713<Mfiyu a [‘4‘ H cove! W A ,3 4 Removal of a methyl hydrogen by homolytic cleavage: H H [We 3—: we :1 435" H H H ’M (Illa/E . Mal-C awe, Conclusron: Afgij/{f Why/=5 jie/EGJf/Lht (:95 If 6?qu /€ one W . - [J J , :é via/14;: 54/569. /I{ > A” > H {H ,>’ H H {’fim H (Silica/MAS; Wh“ my ewe a“ emeMA/wg/ 5*» g»,- ore Mead e0 - ~ 7 2. o W —- [cf/Lamacvgb @ CH 0L 4;“;ng a. Qfiigtc/fi— W 3 (19.14 1% l m... e. Cf—fIZCHE)’ :2 CH (er—r 3) 2; can/pal, fij I wasn‘t/k m E (We —— @ Reactive intermediates in organic reactions Recall that an intermediate is a chemical species that is created in one elementary step and destroyed in another. We will see three types of reactive intermediates: carbocations. carbanions, and radicals. Right now we will just consider carbocations and radicals. Carbocations and radicais are electron-deficient and may be stabiiized in three major ways. Structure and electronicconsiderations: N 0111: A a: r (KM -cL—vcot S 2- ‘5 ‘1‘ . 85mm?ng 5 ° pf fiat/p / €53 KEV/56:21.5“ €33), 3 a j arr/veer . y / m cos -a, {121.60% 919% sedate mcfeoffié’fgfi. How are carbocations and radicals stabilized? 1) inductive effect from alkyl groups attached to the electron-deficient carbon 6 6 e, 4- GK, 6. ,sw arm/{giro refit, age (>th (%L.CA:W&_ 6’ I We as... a, a ft, mOLC,c;crt/€ {xi/L MQKQQ 1?. (it 0443 W- - 5 3 . 20"“ sflgfif} 3 [/fj NOTE: (S' maria @ Mas/s X, . H C 3 Legacies Me £299- cfimgjwms H c: i/7 Rx é‘H H C/C)\ «Snot/m. awe! 4%,“ko us ‘9 ‘3 5 3 .5: £— a . 3/ j 2 f» a me (ea/s4.” s 5 ‘9 - 3/ re. overlap etween a filled o moiecuiar orbital and an adjacent empty p orbital Jmf’ ‘3 2) Hyperconjugation: h M “K arr/4mm ‘ m. anew CW {EH £539; Armchairs/€12) H/.l /i-i . + r + (3H EH +6 H/ . -H (arng > (Ci-3323214 > $ 2) r3. H 5 M6 3) Resonance delocalization. where possibie we: .I Selectivity in chEorination vs. bromination of propane If we compare chlorination of propane to bromination of propane, we get an entirely different product distribution. This increased selectivity must be attributable to a difference in rates. Bromination of propane (HBr product not shown): CH3CH20H3 + BF2 _——“" CH3CH20HzBr (3%) Ragga“ 2, a “ “"- “E CHacHBrCHg (97%) Km! “H Again comparing the enthalpy changes for the propagation steps of interest: Ragga/"H 9 7’ . ' WM 3 W Am ‘ vie‘tawwwag}. 10H 1 wemwer a 4,3 5 r may, AOL CL C" 2585, e jg L . , c ‘ wax/W a -- ‘5' m act/tut” H H 606 +6?— GQ F - m ofiaexflxxa ———-——>- /°.c\ + rim—£5»; )- AH: +44% 90 H/ \CH’ZCFEB H C’i-t'g'C'aL-é:3 Mar—’6 “(£14. chrgflulmw) “EKG—tfi/E’Jtmts) “BEnc/E = 46f e m: " (5.?ch 2 43513ng 00 i f §$afr>qfic¢CH3 “MW-“>- /°C\ + Fifi/{L} AH: +31 in 3 3 0 3 2/ Mat/{cw éjOM/a-CW'iAaq/ gg [6% (1 ) Ehomwmv "t/é We, Sweet/Hm m (Viewers 97:; :3 ) (Fmrobmtfk 60:40) fihemww'filw «Le Wcirflfie/Lm/Lu foo/“fa die/'6. 61%,}; afiewwmzrw be r: mo'Z‘gomw/Lc {a fleece, (3) , MWCQ. M 43AM GRLWLWM ,o 2 /3.Wote (I- & 2—3;,L55‘Cgfi C fefloémmfigem: wfli/ (if-Mex 33 ~3ff~ [fifim/V‘M—a’e ? ’fi'w‘c‘t/Ekmnea EMWWCAItL—‘onm: wt... 4.4 £3 —§.. 81‘ SCH/v1.3 “ @ "7’15 We use the Hammond postulate when comparing two consecutive states in a reaction profile: am 7!} W Game/W, WWJ‘EL‘M sitar/ii 53,. £10m 0W game—twee , flametmit fit, famed— Wfiafie WW “is -05.?va 7:6» «effie, m m : There are different ways to state the Hammond postutate: a \watwoniWLe, .. 42"” W Hammond postulate e ‘75:?) W5? innit: fiwctmee 6 ‘ WWW/66% GWWr/‘twu. fibeofie/s (Madam/“(is defamatme 790 writ/can as a, flame/4W W. How does the Hammond postulate help us understand the difference in selectivity between chlorination and bromination of propane? 00m -me. W (Pt/Con, new o—fi, Awfi—oteW-W (73’ . . , 0L. S W " WWW §< a’fi/Eo’mmmtm; Memmfixna, "x fianstfww must-aw we ‘9 “1—25 - tetra" A - “5””in / “312$ (ism/1mm - ( at m max/Lot #0 wife) foam) 615mm item 8;? Wad/‘5:- m M I <1 I a . Wu ‘ ’fi-ULSP/gécxfiébli \Nm Nejé: E vmw 9L5, m 34 04A; “a: doom .5” goat)..- J'A {:5 Sag/L?- M 0‘43 Mme, Ajvv 1:1an Non” Eat. VO‘IW 53‘ m Bdowwémmw 05mm magma: umEoomww Rm “268% Ehfiufi “Q mhmfiouafimfim Mo “KENMme Q $3me 3583“ 6 manomfioo 893 Am ommwmaaoEUfiAmv § 835.5 “333% Q osmwmaouoEU§A§ Q .Ew: ho 3533 .3363 SEEEHBE 2: .8.“ ESE Nam gamma 2:. E m conga“. an $38 uamwmnoEcE-mAmv we a “gamma mama—Hm “£58235 ion—Eofifia .Amzuzwgm aofimfiaofiu :2? @8333 2: we Rmbmmfioaooehfim 2: ummwsnmopoEu§ 2: .wo Hmbmwfimsoowufim 3: Sasha 8399:“ .EEEE 3E3?” m gunman Ewm mo 35min .mmmwnnohoEuA “Em oufimnonofioé .wo 252$ m 23 E N $530 an ozfiaaoEEFNAmv mo :oflwfiaofiu m8:on Em: m0 35mth 33 5 SEE: mo momwmmfiofiu wig AQ ESEEBEQQN E Eé G éfiéafimafi,m “N Q 8.2; Am BE men a e - a £223; Egg ammfiemfifiwggm Q $6:on mommflEcEuomoE Cg? .NMQ Ema wafimfikgfig 3mm mwfim 33$ ,«o geEomm fincfimfigou €33, 5N mugfigg $3353 9% E $353.5 aoflgficggga ,3 Egg; 9% 3%95 ...
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September 26 - October 3 - agitate#6 err See-Weft w eta/62m...

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