18 - Reactivity of Organic Compounds

18 - Reactivity of Organic Compounds - Organic Reactions...

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Unformatted text preview: Organic Reactions: Understanding Reactivity From a first approximation, many organic reactions can be explained in terms of dipoles and charge attraction: ° when two molecules with complementary dipoles collide with the required activation energy to overcome general electronic repulsion, a chemical change or reaction follows. an extreme example (from the world of inorganic chemistry): Shanna vamlvkl’ l°M& Shula lonlc Bull l l Not 0H + H Ca ——-> H——0H i— Nate. “We l1.» Wad Specie; , ,. OH (20 c}: vol 8 CQGD rw uo HM M0" a more subtle example: 0‘ 4— Shot lOAlC W modal \ooul “MS GOV Ila" l’O‘J l 3 load l @963 H c -— CM +— NaLEr 3 63" z". 033 'l' N0~ ON '—~———> ' . d 8 3’ 41¢ Msoill’Qlfi OlMJcS—QA QfiMZoL: (axe/l1 04l- ‘l’LJ_ pale'mll3 pon‘thls Q/lMA/B ka 01A Wt Com wSe\\o~rrw$I‘ fl [email protected] 4— “Sc—CH [gr—CH} + 6c» -—-> +0 ludloocl'c hm. Qlow Cl eleleDU l‘* a. ‘(ekol‘lo-x.‘ Mm“ Weill 00% lpccoh. ’lw. +145 analysis of the reagents in terms of bond dipoles and electronegativity allows you to predict reactivity (to a certain extent) Organic Reactions: Understanding Reactivity Additional examples: a charged species can react with neutral compound 3?; «he, wgsocllvelj eta-I11 NC“ CD + H3 39 “*3 “3C cg 3 EEerllb fOSl'llv-Z duugcol 6 caxlbbn : GEN: é Sou. Whol‘ \MUA-L ‘ (D 'lfbnml ('3 ($1036 0» Qo-(Lon S L065 'l-o carbon, So‘l’kfi (1:0 ‘loleC W M VOW two neutral compounds can react C“ Md “HM is (“065 WNW a mm 04““) S9 OQ +3.9, non—Lsnoltol Clemflj Q Sf) + é» c/‘\ l,‘ ’l’kt N lune patlw (“J Rdim“ E “3"“ H36 C43 3 ‘*3 NH all: voll’L la Faxlw‘allfi u G) 3 '?0$.\R\W. QlMcSzA WLM F 0&9 9 ll 95 \ @o/VF3 ll ll vx “fivelj / B E 13F + /l\ “—‘9 l)” ‘* 3 03 m Wl‘l’k le‘hllS reosillwels lvx all 0‘? ‘l'lA-QSC wag mljsb G‘p “lid; dwxgzcl LorOh P "8\: bowl Md Mecdw dipole; w lxalp 34w 'Inl‘all‘ 1%?+3?_°vgah‘ ‘l'lNQ WM\ (QLHVl-LY Curved Arrows: A Formalism to Indicate Electron Flow Curved arrows can also be used to demonstrate resonance structures remember benzene? WWW W“ Edema?“ YQWQ’Q SMJ‘V’Q 14%?fififl / U dimethyl formamide: 09 ”6|ch “KM?“ m 51,2 0 2 K 0 Law tad +0 a‘louo . H C DA H C 4"" “mi in (3613\3/L H ‘_/_> 3 GB'T/ H <__> 3 \r/‘LH “a“ ° l C4) we, CA3 04+} “is ”‘31“.4 P 09.91le rd— OLOuQBQ is mew-£4 / 1+ (1+ a” l anion: \ J _ x y Who-A {S SP?— hflLflAl-teg‘ WM- ;; W‘ “Ca—‘79“ ‘L'Jr m Q H D {b \(e) ‘oavdor +0 towgq «mamas. f® on: C—é ”\l/\ c1+1 <——-> filo—W H N —- C lewd? Hr H a awfo h raid-65 {A 1) o/‘oH‘aJ +5 fyM|+ Aelocdrid‘on aHyl cation: Q H I+ H ® CAI/1%“ H HW k—é WY T H ” rr H ” Ski Lskfwkl‘fd QAJBOA My, 70A. m+ wikmmcw} ?’°"°M (QM Emcefl’ 4m») Owe/w 7W, “”5““ Curved Arrows: A Formalism to Indicate Electron Flow Organic chemists use curved arrows to represent reaction mechanisms 05 09 N459 6 t ea + aka \S MAM 90k) 9}teth fiww ‘lTDM‘l’kQ CH cuiknldw. Mich l’o JFK-Q, Wl‘w'jl (”“33 6“ “3 N 1' Qfich/wz -—’“> H3 C/ll\ C4+ (yawn clMA+S 3 Q) vale] +0 l’bfil S ““5 “H3 . WM push “-3 E) o zr—ABFB ®o /RF3 at: (k “ (muslin . H B}; 1' CH3 /ll\ CH3 '_-——"7 H3 Q’ (4+3 WNM algebras film lrom W Wlfi0k3l lame Palm +0 llua vawl Belem p—olbll‘al “pushing electrons” using curved arrows: rules to live by ° a curved arrow indicates the movement of a pair of electrons (NOT ATOMS) 0 the curved arrow originates at an electron pair (a filled orbital) 0 the head of the arrow indicates the final destination of the electron pair - overall charge MUST be conserved in a reaction ° the octet rule MUST be followed: if you make a new bond, you MUST break an old bond (Ml ill l4? M Why are Alkenes Nucleophilic? ° the filled Ic-bonding orbital is the highest occupied molecular orbital (HOMO) - alkenes are weak nucleophiles, but will react with strong electrophiles (H+, Br2) (gr “llama; 'WIOM; I; USN» ln W33 m Lflslm ( 0:; low-(l, “TY Luwl. Is ll’DMO LuLMo ’,_\Tl-:C’ a/Fovu PLSL‘ll/kfi .- orbital l \ I. ‘§ energy 8 1 'o' ‘x 4 g H f “‘ '1' F \‘ " Nucleophiles Nucleophiles donate high energy electrons from a filled orbital (HOMO) to an electrophile in OSMl l W' loowolflé (:65 0.10. Lisw it vleraaA lac-AJJ «5 dew-«5‘3 Wage lGVUz fall! cue l—‘MJlmlb ’l’lLQ JD ’llB/ a erOlflc/klpe neutral lone pair nucleophiles: W 9W daring Chm—C —Pflrs> cue S’lllolllL-EJL % S (:2. R", B: mom. zl'Qr/l‘fbvxefiadnljxp~ H DH H3C’ \CH3 ”’4 ’H H3C’ CH3 allbms /o-z loll'le . ’l’wo lone air; (Mel-llama \an CH3 wk L km W lai W . 3 \ t l . r. [o M 5? lnglonaliieal D \all'hlS in a" 5?; “bloflcli l I ”*3? anionic lone pair nucleophiles: 6 gm HEW), 0“; °’ 3 I f l WL—lf)‘ ‘5 MIQ, “LC/(.QOPMLLC? @ e e e e 6) OH SCH3 CN I Br Cl nouo 30w aclwall3 l’Wth, m ne‘l hefimllm M” Q” 'l’hi; mixes 'l’Lo. 6.421133 0'? M HOMO] Swolb ‘l’lML‘l’ m £95 WQ Mfg “3,64“.ng +1, W neutral n-nucleophiles: H2N Ho ’l‘ , >_<— >—< >—< ; C E rxl g/M’l "l Me 0" Caxlaon. CAa/Lon \‘S lCSS EH ‘l’lmx N! m HBMO f5 lullslxer. NllYllQJ out \MAQleOPHJiC 0n QA'LQA- From Last Time ° nucleophiles are neutral or anionic species that donate high energy electrons from a filled orbital (HOMO) to an electrophile - electrophiles are neutral or cationic species with low energy vacant or anti-bonding orbitals (LUMO) that can accept electrons 3 \ ‘ . Ll \ S? [F TSFI is M clEle'opkile ll \@ Eg/ l: < > ————%> .N “ u. u /°N llfill @B\ W -/ 4K \FP H s F H l ammonia» \‘5 k F MN 67543 (DNA nucleophilel m “N Orhll-al ism firm/to ° organic chemists use curved arrows to show reaction mechanisms 0 curved arrows indicate the flow of electrons 1m 63 9 w H r BF ————9 (gNrfifi 06 [Jo-Q) l on N “3/3): 043 Electrophiles ° electrophiles are neutral or cationic species with low energy vacant or anti-bonding orbitals that can accept electrons Protic and Lewis acids: Vam‘l’ l5 Ovloll'wl Halides or other compounds with weak O-bonds: Cl—CH3 89 8'9 Br—CH3 +0 WSW ME ocllcvsl MMQS GJQ flux; e/leelv‘ophl Sf alSo With)“ O'Ll'l'uli wens—ails folkdhlfim can LQlVl lav} W docu'l 5wa low. “(Idngl‘owb’ I—CH3 Br—Br \ / M32 Loads are Walla polan'td all All.“ Bowl shcocSl/k Mail-EM; ato m Cl Br EN 2.6 4.0 3.2 3.0 2.7 2.0 2.2 Why are Alkyl Halides Good Electrophiles? alkyl halides have low-lying vacant 0* orbitals that can accept electrons PM WW3 ‘3'“? other important factors: “i” “WW?“ 2 as (kcal/mol) 32 (kcal/mol) ° bond strength of breaking o—bond ‘ _ \ H C_CH 83 decvmle . ' («crew 3 3 “idem orbital overlap em QM3 c,_c. 58 ’2 a? “3 - ability of “leaving group” to stabilize negative charge 3,-.3, 46 mam ova/lap I—I 36 ‘ Orbllacl 0N?!l v.3034tlcol‘mpbllQ ‘ is lots; Behotgn [’é' (HDQGGQQQ HLMO lodge-r mellx‘ciwl 0—142 “ks—MW. 0.3 \{OUL cow Sec-I W395 5m? 3‘ ‘\ Si“ 0* Wl’wlr- ““¢l¢°§al\llfl ailuclc WLM ol' laan Aipoles mLe 0~ 003 “M °~ C x‘.'—' mm Will La {Jr cg; mu Piclve W‘ 2:33 orbital .5 Q "I l‘, Maemislm ol Maud l’ llf—“CQ in ‘le’ms S —‘ | . energy l° ‘. ‘3 Di, wake om! Mathis ~. 2+ 1H7 49 4e w m m \ ,v G x I m REGARD-a \ewo ———> ‘ bow lam potlQ (I‘ca) / 5? H at °CmEDCQO Hfimo alle‘l “C— mull Ola/l-l ED (Tc—Q\ HE C. —C\'“H + Ca (“32/ Qo—chb‘q'ekl‘ H OM olAlotqlth : Mm EN azl’nm Mg MEL“ POW/Wow cl» 9.‘ Wily}, The Carbonyl: The Most Important Functional Group ° the relatively low-energy vacant 313* orbital makes the carbonyl a good electrophile ° the relatively high-energy filled n orbitals (lone pairs) also allow the carbonyl to act as a nucleophile (a weak one) we Qt Ms: W3“ “final W who“ ‘ ' ‘ \ lee hl Q) . loo-uhkfi alloll'uls on. low M W33 M n Hum... nmc l3 “cg/lune I Ase honvlyomllhfi OM‘lRlS L 03le rchlvmalj ml‘ Cuban :0 . O'— OVL’ll‘QlS W {‘0 Le low)” (4 W33 H c/T T m 1- New {g ”at (two) 3 SP1 SfL Q0 \ orbital C? +/ 4|; 41,—‘3‘6 OM rd” :HOMOJ) energy ‘ | ‘ 2 lane air “‘ [3 \‘ \ O ‘ "fr F _ll Co - the carbon has the larger ‘coefflcient’ in the 113* orbital, so nucleophiles attack the carbonyl at carbon The Carbonyl: The Most Important Functional Group 0 the relatively low-energy vacant 313* orbital makes the carbonyl a good electrophile ° the relatively high-energy filled n orbitals (lone pairs) also allow the carbonyl to act as a nucleophile (a weak one) examples of carbonyl compounds: 0 ° 10% O / /\/N\o A/U\ MK” /\J /\/U\T N H lzezlma aloLclxvde» 25% wide Chlawnll a acid. a O Q acid diuriaL-L %k13“l°LL ul‘l’lq l0 Carboxylic Acid Derivatives: Variations in Reactivity ° the electronic nature of the group attached to the carbonyl carbon greatly influences the reactivity ° the effects can be categorized as inductive or resonance Lil” \ O . % rollol'l'klf “A ream/hm K/lleC/Q OVQJGL OHM’DLo‘ : ?flwil1 idwvl’hla, LW/l {5 if“ 01-?— A1) Cl is W dephkeflk'llfl( (3:: M313”; {A WM 0 O . . . . K/lko )Kll ’ ”Hyde, «is lCSS «Ml. lo ‘ 0 cl: Sue MW33 $2542.31”; W 2,“ ABM—M l iniKC—l‘ul" gr 500A Mlxlkj Wl-l’k Mllll O “)5“; mtwl 53 naming the wtwsl Tr’f.. 1 8+ \‘lH-e. 0W 0w QWloOh rumMCL MM“ R /ll\ 0 K ablir la 36 [\S :‘Llh A Mi“ W'Lwlv o M % LEA-El; H a» N/Wl‘s O-NA ll"? I‘D—Gle‘l‘KlJ are, we,“ Mlokeol/ ‘ (MK 3 log \%~ _ nib/by?» finale: deal/2M Mtg 3 / Q43 g3 (€Somuxu. Also is l-edJ‘ ole o'leAfjbdlM( ell "m Mums 4» am Hm lone. far. 60 Nun. L ape IR Spectroscopy Tells us About the C=O Bond ° the frequency of the IR stretch of the CO bond tell us about the degree of single bond or double bond character 0 O O O RJLCI RJLOCH3 Riv/CH3 Rice CH3 "100 ~ nBS—WY ”$04433- lU‘S‘WYO 193°" ‘5'5° Cm" A o FOSMMDP— dUNVK/lfizn W\‘[ 30' k/Lk F Rag/we: 44M; Q=O dakocflx‘eecma [QM (gush ’- W More A: 4’“ (—3 Me— WM gmfik howl Wee/Fer. hams ”Mk“ $422}: “gyrpe. 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