Exam2 - Answer Key

Exam2 - Answer Key - NAME ANSWER KEX Chem 268B Midterm II...

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Unformatted text preview: NAME ANSWER KEX Chem 268B Midterm II March 12, 2010 CLOSED BOOK, periodic table attached There are 6 problems (do all of these) 1. a) Draw the structures you would predict (using the 18 e— rule) for the mononuclear metal carEonyl complexes M(CO)Xn+ 0”“ of the metal centers Cr(-2), Fe(+2), Mn(+1) and Co(—1). To “12- crz- ; c12 =7 oc—crgsz Ico Cofl‘; &‘0 73> 2+ - 6 ~--— , Fe ‘ d “‘3 gsficgé: $° 7— C0 7 /CO{‘CO r - 6 __ ‘i" + CC C0 MA . d ‘7 OC—Hm-Z—ig 0c | co b) Draw a plausible structure and give the electron count for the complex Ni(n3-C3H5)2. '11- 8 M )ct) ’- “1.0 a (i What would be the predicted vague of "x" if the Mn—N—O bond an ‘ ' near (180 °)‘7 ‘ 3 5W3?“ 7 Meow =3 :Nso: => Ma‘,d‘3 =—— p (51190109 L1} 0C\ Mn :21: "936) ® é (ii) at would be the predicted value of "x" if the Mn—N—O bond angle is bent to ~ 120 0'P? ‘ 0 1 /2o*> —> 'Qfigvo: ~——> Hm 016.7 » v K - ,, _, , ~ x ~ 5 <7; 9‘0 1 O C. V, N‘W w CO fiW‘LWN? aim-M1 09” ‘ {10 {if gdxmm / m Chem 173B/268B exam 3/12/10 p. 1 of6 " 5 Smm'd 2. a) The actinoid cations (An3+) show a gradual decrease in ionic radius with increasing atomic number, known as the 'actinide contraction'. Briefly explain this phenomenon. MOAO'i‘U/lic (DART/Lem 0-35 Am (511‘) WWW; {Callus Causal ‘99) poor slate/Ming o3: nuclear Qi/LQFj-Q bub 5F gleam; (5W3 {w L‘Mlth{$‘l’nL (“kt/+5,“ wlAULinP/I W) mesa. CUE b) The infrared spectrum of the uranium complex [U(CO)(C5Me5)3] has an intense CO stretch at 1880 cm‘l, significantly lower in energy than free CO (2143 cm'l) (J Amer. Chem. Soc. 1995, 9, 2649—2650). Why does the corresponding neodymium complex not form?. LH: doe, buried OU/LCL VLO+ Otv’aiithk in) 153x114 loom/W8 lAlEfatchkM§ Specificallj L11 ~>2 ‘11“ (,0 (/1 Crtclfir 'Fer slang; 4 <thducfirad3; fill cmdw {20, NCO ll due (‘0 $00 bmdeulw 0le +0 55; ——-2'T* barkbwdflwlv w sow-1W \[Q/a‘éxl/fl WMO‘F) Chem 173B/268B exam 3/12/10 p. 2 of6 3. The rhodium(I) complex trans—RhH(CO)(PPh3)2 is a catalyst for hydroformylation of alkenes. R—CHzCH2 + C0 + H2 9 R—CHz—CH2C(O)H Mole fractions of inlet and outlet gases for a continuous reactor operating at 130 °C and 20 atmospheres are given. “Other” products are propane, 3-methylheptan-1—al, and butanol, and outlet gas compositions exclude starting material gases (propylene, CO, and hydrogen). The reactor contains RhH(CO)(PPh3)3. INLET OUTLET propylene 1 5 1 -butanal 5 CO 70 2-methylpropan- 1 —a1 0.5 H2 1 5 other 0.2 Two partially complete catalytic cycles are proposed below, showing the formation of the principle product as well as the principle byproduct. Where requested provide: (a) number of valence electrons (V.E.), oxidation state, and d electron count (1 pt. each) (b) regiochemically-accurate drawings of the key complexes A and B (5 pts. each) complex A (c) Research suggests that migratory insertion is rate controlling in this reaction. If the inlet fraction is changed to C3H6/CO/H2 = 20/60/20, propane production increases by a factor of two. Circle, above, the intermediate responsible (5 pts). Ffill ccelitt‘ M dwell/0) oiYLLUC’ C‘ Chem 173B/268B exam 3/12/10 p. 3 of6 4. (a) Use electronic configuration arguments to explain why 18 Fe(CO)5 a trigonal bipyramid while Co(C=N-CH3)52+ is a square pyramid? Draw the structures. a w // ML 4 /w.k./a smtrewm $8 9 mfitmiflé‘wwé I?“ («(35314 ‘Frelol 5F\if¢fljfid (10¢er ‘[email protected] CW NVhVVWk U} @wrw my! ([0 CHM 723— / , ~— L‘ 714- ”Qvflco ”- — (' xw'w ” (“4“ L;Ca_fi @ OK ( QCL} % % NEC" ‘0\CNW : .21, 9‘ 'x ‘5‘ 3% l ‘ l0 l E “W 45* 94 m w A? [89," LL“ » C 1+ 1 3%: W“ ”3'1, MW l l 0 16% I id6l‘Nl’5 “(1?er V j (b) HOW WOUId YOU expect these two complexes to differ in reactivity (i) Which should be the more reactive toward ligand exchange.?? E Co (CNHQ '1+ 1 Q) ’ E (ii) What reactivity would you expect with a halogen such as 12. ?? «QMthciy M \OOW C066"? Gull lcnlédd) 6)? 01‘ MCOMPWQS , 1&ka + 1'1 -—> [£14ch + co @ [fa 2+] d6, 13¢- owl Co (cum): + i :1 __, L01<CNMLS:+ (p :3 (cw Mag Oxccep leek CantUL it oped + l k. 11 (5) (a) The second-order rate constants for the Grail+ reduct' s of Co(NH3)5(H )3 3+ and its conjugate b ;W are reported to be 0.1 M“1s—1 and 1.5 x 106 M“1s—1, respectiv Explain why such a small difference in the coordination sphere of the oxidant has ch a large impact on the rate. CD(IUH3)5. (0:43“ oxidic'iC) C(01) bgAiMef 59km elfiom‘fl ‘lYZU/leCK (MCI/191nm”! - (M 3+ H \ . @ camp; (H10 “ ‘ 1 W a £\ H u 1\ S (b) The pKa o 0(NH3)5(H O is 6. 9 At what pH are the rates of these two pathways ' M :g‘ ‘ mks (1%qu <—> a) )Ll/{I 1L {:3 owl 2kg [37”? {C9 27111 W 32.25 117M114; 31M 7:: 1V : {LIES _. fl {3ch 91113 1. JZP‘ 1% Pam “53ng (0) Assume the starting complex Co(III) complex is the 180 labeled species P H < 0~ ~ - “’0 I 00 Co(NH3)5(H2180)3+ . Based upon the explanation you gave above, what products do you predict for these reactions? 0 la 1%“; “ . ,. EEM Md muff 1+ ,3 ‘ 0 C0 LS (56,41) 3+ + ((2 e'yzkslu EIWZN CO(H7'O)6 + £(.(Hzpé 1 ) @ $11.: ““5 + 51, W HL’ZD . u— (1" 3.0:; 5* L (:0 L5 (”0”) I’ C 917m 3417 @(HWOLE (r W (M MW 41% mg pmperlj 5W0W‘V5 we 11; 'bHSTW (d) Write a rate law for the Cr2+ reduction of Co(NH3)5(H20)3+ as a function of the acid concentration [H+ ' ' Chem l73B/268B exam 3/12/10 p. 5 of6 6. (a) On a qualitative basis, describe the nature of the bonding between a metal ion and an olefin and the bonding between a metal ion and carbon monoxide. Illustrate this by drawing the structures of the two ions PtCl3 (ethylene)‘ and PtCl3(CO)—. Mm Mm lam ; Maw /w 6M ”WWW—e rim 61w; - affirm {ram r\/* ' , é , ()\M\ ’9 DEM TV’QMLM i aim» nu, t GOV/(Alma (b) If we replace the carbon monoxide 1i and of PtCl3(CO)“ with a thiocyanate ion (SCN‘), two different complexes with the same empirical formula can form. Propose structures of these and predict which you expect to be the more stable. Rationalize your choice. lDtClchO)‘ + W .j’s:¢=,[email protected] ”H ’77—- ? W730 «CO C‘;Pf~—S\C\ @R @ C\ \‘N P 0/0: 71’ f) 0- “t "N\C v (4% B \s more B’s‘lu‘olflflm (abs/W) 01 V7)”: NCS C9Vb\+u\ <9le cwuilm -B~f0r‘ctbk f3504+ qthX/flhft‘bcue New 0 *9? Law 5 dot 3%ucmwe5 6(de ‘ H 5%“ «app 3, 333CZ’3 5 CZN: Chem 173B/268B exam 3/12/10 p. 6 of6 ...
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