322bf05_plq1_1

322bf05_plq1_1 - CHEMISTRY 3 2 2bL 2 (13) Lab time 3 (10)...

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Unformatted text preview: CHEMISTRY 3 2 2bL 2 (13) Lab time 3 (10) T.A. 4 (9) 5. (8) This test comprises this page 6. (10) and snare-n- numbered pages . 4' IX TOTAL (60) If a question says to answer in fewer than a certain number of words, do so. Also, Qengtign if any part of an answer is not responsive to the question. ts at may — p labs” Apr 7 t; ough # finly first/half hour5}_-"=an . offi-ceg‘uours. 9:00.: For questions/“about this qgaiz{. st . V V M WK -1- 1. (6) Recall the Grignard synthesis using n—BuBr and CH3COCH3 to produce 2-methyl—2—hexanol, n—Bu—Q(Me)2. OH (a)(4) In converting R—Br (A) to a Grignard reagent, "RMgBr" (B), the the coupling side product R-R can arise from either (1) reac— tion of A and B in solution and/or (2) from direct reaction of 2 A's on the Mg surface. Assume the rate laws are simple: For the main (desired) reaction, ratemain = km[A]; for side rxn (1), rate1 = k1[A][B]; for side rxn (2), ratez = k2[A]2. Suppose only side rxn (2) is important. (i) Derive an expres— sion for the ratio ratemzrate2. (ii) From this, tell which conc(s) one should keep low during the reaction; explain briefly. (iii) Tell how one could carry out (ii). . N/é‘mm Z Z L 2 M 2 M (9“ V q. 14 mt Am: Q or) (my) [)4], ma: M4» < em an MN I C‘C ,4 J/OLJ/ C Wot?) (GHQ/Q. O ( Q 7 (a), V X_M (b)(2) To convert the Mg(II) salt to the alcohol, even very weak HA‘s will work. However, to avoid a difficult separation, what property should the anion A" have (or not have)? Use <10 wds. fir {cloth/f M K . JMW'W Wo/ M? (at 2. (4) Recall the Pd 2 H2804-catalyzed alkylation of anisole, Ph-OMe, by Ph3C—OH, all in HOAc solution, to give p—MeO-C6H4CPh3. (a)(2) The intermediate Phéc—OAC is unusual among carboxylic esters in that, with cat H , it alkylates rather than acylates nu- cleophiles. This was shown 65 years ago by its reaction with (fin l7 MeOH. Draw the alkylation product. (40“ cat acid h 8% PhBGOAC + MeOH ———————————— —> p 3C‘OMC 7“ o} g H M-t 0 (b)(2) Circle one choice among words separated by / : From the slow formation of the ultimate product compared to that of the intermediate a the path to the intermediate must have the higher / AGactiv, and the I more / nega- tive AGoverall rxn‘ _~:::Z:::::::::::::::f____—_fl*_______________——_———————————————————-——————--——————1 :13 -2- M 1 r 3. (8) Given that the rate—controlled product ratio Desired Prod to Side Prod is 80:1 at 20°, 2:1 at 70°, and varies exponentially with T change: (a)(3) Calculate the rxn T to give DP:SP = 16:1. Use care in defining [ET in the expression rate ratio = some exponential function of AT. (b) Calculate the DP:SP ratio at T = -5°. (c) If 1.5-2.0% SP impurity is acceptable, tell why getting higher purity by operating at lower T might be a bad idea. For full credit, derive all values of logs from 109102 = 0.30 and/or from the definition of a logarithmic base. A 4! iv = 1(‘1’19 /" AT." 70f7p / ~_. \— - 'N 4. (5) For the evaporation of dilute aq ammonia: For y = amt NH3 in soln, x = total soln amt, and r = the vapor-to—liquid NH3 conc ratio, ln(x/x0) = [1/(r—1)]1n[(y/x)/(y0/xo)]. Taking r—1 for ammonia water = 10, calculate the conc of NH3 (wt %) in a solution originally 5 wt % NH3, after 15.0% of the solution has evaporated. For full credit, approximate ln(x/x0) by —(fraction distilled) whenever fd < 0.2. 7? WC : Sou-(“K2 x¢7’7’3 A? W (my? am £K(l-§,{)c,éq(akr]’ : «New a m wear“ 1 albla A/AFMC7 n: /w a K‘+ -3- fljzcm 5. (10) For l—hexyne, Q'C4H9CECH — — — - --> 2—hexanone, n—C4H9—CO-CH3: (a)(3) A student attempts the reaction, and is pleased that very little (side reaction) darkening occurs. But the reaction mixture also shows almost no ketone by 2,4-DNPH test. Explain in < 20 words why the student should have known that in this case, little side reaction means little desired rxn. Consider the nature of the desired and side rxn intermediate(s). Wmfl (ufiw EM . 94m 77 m VC =7 mwmfig’vfjéfl‘KX /0{U’(2(6%f’ (:QK'f/L‘\)- (b)(5) A vinyl cation, VC, R—C=CH2, is a very reactive electrophile, which typically does not discriminate between strong and weak nucleophiles. Yet in this prep, even though the free water conc is much lower than that of unreacted alkyne, water does compete reasonably well for the VC. Show electron movement for each reaction of the VC and then explain in <15 words why water's rxn rate, adjusted for cone, is >> the alkyne's. 1531 (£IECH k—CZCH‘L R‘ ’6“ fl‘cw (4/6/74 W widow/(W W “’l" $-39 AK“ Wt‘flx «HQ/M WWW bet/AA: (coda/(«.205 . (c)(2) After "salting out" the product, its solution in DCM contains a little dissolved water, plus some droplets of saturated brine (satd aq NaCl), relative humidity = 76%. State what fraction of these droplets can be removed by a drying agent 1: system of rh = 38%. Give explanation and/or show calculation. /’ ,4” (a. moat), MM) ma 7% WT“ 64—4de (JaZ'Itf/c‘é) M f M: W “1 2%.,”m mcj 6. (7‘ Recall the isatin/acetophenone aldol condensati I O (D u n O CH3-C-Ph l H Isatin Acetophenone (2,3-Indolinedione) MW = 120, d = 1.03 MW = 147; mp = 193-1950 (a)(3) One of compounds above reacts with Et2NH to form a nucleophil— 1L ; ic anion. Draw two resg§ance structures for this speEEes. C{wt fill“ Q (I 6—9 ...' ?% 4M1 :Cch‘érflk C(h‘C'Wt (b)(4) Compound II results from the dehydration of the initial aldol product, a fi-hydroxyketone. (1) Draw the structure of cpd II. (2) When II reacts with Na28204, the intense color of cpd II disappears. Tell in <10 words what electronic structural change is occurrin%§ cal—£70k . t W674) (2 fgfio (7§f<mJ§/5M€1 éN/(th @ «@ 7. (2) For a reaction sequence 1A a 1B, A limiting: Exactly 60 mmol A is in 150 mL aq solution. From 50 mL, one obtains 12 mmol pure B. Calculate the % yield of B based on A. fl owl/(Mk 0% [5? ML W flan/‘3, {/33 %m MMM/ 4%44““h’ I (6/;fl =- (j;5922 0M ‘ WW9 g 2% 1044/7/44”? 76% ff is? - 8. (6) Consider the methyl benzoate prep as performed: cat H230 PhCOOH + 30 g HOMe -———-—-——-€>— PhCOOMe + HOH MW = 122 MW = 32 MW = 98 MW = 136 (a)(2) If one takes 50.0 mmol benzoic acid and gets 63% conversion to the ester, calculate what mass of ester is obtained. A 63%V “Win—- 7" s 3‘”, 6 emf“: 0.03N'w44.‘° (3 C mm M72100 '/—\W W 6 —- \ (b)(2) From (a), calculate the yield of ester as a percentage of theory for recovery of 22.2% (2/9) of the PhCOOH. _ 6 3% q % WW ’ Fifi z @333 *7 *: 55% (c)(2) Tell why aq Na2CO3 extracts PhCOOH but not the ester from a DCM soln. Use one or two sentences with < 25 words total. 0K 1L” “6; mum 7!» W‘Jd/ 9. (2) A and B react to form C, with Keq e 3. C is easy to separate from A but hard to separate from B. If A dissolves B and has a suitable bp, tell why using A as both reactant and solvent can help solve the separation problem. Use <20 words. 74/. A M gwév W44 W “M £7 [AA ,QKW Awffifl B WlLVW/ of W (0v (mm 4 a "6‘ flquo lO.(lO) Benzaldehyde was converted to Dilantin in three steps. (a)(4) Write a mechanism for the reaction of the species below with (another) PhCHO to form benzoin, Ph-CO-CH(2§i-Ph. Show proton transfer(s) intramolecularly. P+ . 1’ ' \ <9 )K/O .. OH H 3 ("pk flee/N H “a 6L <9 K (b)(3) For the Cu(I,II)—catalyzed oxidation of benzoin to benzil, Ph-CO-CO-Ph: During the reaction, the brown gas -NO2 forms continuously from NH4NO3. But -NO2 does not appear until nearly all benzoin has reacted. Explain this; show electron movement only for the reaction that actually destroys -N02_ 0 ((4 ($2 a): [we—0M "9 Car) (duh/Lt Mott/(A) ‘fiflL —‘} U07,“ @ (KL/wot » wt + W? (42% 44/913272”! M M Q"; fl *Wt 144 yank (074/. (c)(3) Write a reasonable mechanism by which he species shown below left turns into the anion of (Dilantin , below right. For intramolecular H+ shifts, just say so between species. CH. N\ CH H 6‘\c¢ C=0 "\5 N ...
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This note was uploaded on 01/30/2009 for the course CHEM 322BL taught by Professor Singer during the Fall '07 term at USC.

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322bf05_plq1_1 - CHEMISTRY 3 2 2bL 2 (13) Lab time 3 (10)...

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