322bf07_plq1_2_key

322bf07_plq1_2_key - CHEMISTRY 322bLf325bL...

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Unformatted text preview: CHEMISTRY 322bLf325bL '3prii‘47‘2007 SPRENG”ZUH7 #z IONof‘cUL, §0r FIST LAB QUIZ "‘ m KEY Lab time 131/3392 T.A. This test comprises this page and six numbered pages. If a question says to answer in fewer than a certain number of words, do so. Also, dedugtign if any part of an answer is not responsixe to the question. TAs will have te Tu Apr 10-—may be there Morning labs co at 9:00. ur TA first. Apr 5 through 1f hour--and office hours. For que ' ns about this quiz, '1‘ A71le 1. (6) Recall the Grignard synthesis using n-BuBr and CH3COCH3 to produce 2—methyl—2—hexanol, g-Bu- (Me)2. H (a)(4) For conversion of R-Br (A) to a Grignard reagent, "RMgBr" (B), consider the coupling side reaction involving A and B in solution to give R-R. Assume the rate laws are simple: For the main (desired) reaction, ratemain = kaA]; for the side rxn, rateside = ks[A][B]. (i) Calculate the steady state conc of B, [3188, in terms of km and ks. (Assume that the units of the rate constants give the conc of B in molesB/L.) (ii) If [31$s = 6 m, calculate the [B] one should maintain during the addition of A to get B in 80% yield. (C) Fm ‘ ire/(lemon ;rQ/&((%¢ 7"? @ ,ZM mg: /; ij =5 E I61“; f1 (if) Fat 3% [0 [its #6 3i, HEM Wf==Zwfig flux, )4 macaw} I (Met. nut Mf‘nlr M Jéawa'oYs 4 6,:7 (mafia! “V351 (b)( ) Even HA's as weak as water will convert the Mg(II) salt of a <) Grignard product to the alcohol. Tell in <12 words why aq f4L NH4OAc (pH~7) is better than plain water for this purpose. )4, ac? Avm% 2164,31 Molué/e M {4% 2. (4) Recall the Pd 47H2804-catalyzed alkylation of anisole, Ph-OMe, by Ph3C-OH, all in HOAc solution, to give p-MeO-C6H4CPh3. The reaction fails in ethanol but succeeds in acetic ac1d because Ph3C-0Et does not furnish Ph3C+ but Ph3C-0Ac does. Draw three reasonable resonance structures for the ester below protonated at a specific ite: ," C) .1—12dEAL O + h *fiPHF d; '9$I “ :1 H u H ~0-C~ <’-* —'O 3C“ 6-9 "O- " Ph3C o-c CH3 —————> -- n .. Explain why the above cation cleaves to Ph3C+ much more easily than does protonated Ph3C—O-Et; use < 15 words. 1 QM ( flAGC'ig-Eff (Qt/Lhaf Mme Myer-a {W (Ways M ASK-#7. _ 2 ~ [1:7 1: ::(/ 3. (6) 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)(4) Calculate the rxn T to give DP:SP = 20:1. Use care in defining AT in the expression rate ratio = some exponential function of 4TH (b)(2) If 5% 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. @ C“) m M» = (200% N“ 704’ C41“) m0 Z‘do __ 47—- __’._. 1.32%’/¢,+0.3—7?5~Lé$ AT’: Elli? ¢ 7-“: 337,75“ (3700/9 @ (42) Km wnnzcwcm'é’ 5/040. 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, 1n(x/xo) = [1/(r-1)]1n[(y/x)/(y0/xo)]. Taking r—1 for ammonia water = 13, calculate the cone of NH3 (wt %) in a solution originally 10 wt % N33, after 1/8 (12.5%) of the solution has evaporated. For full credit, approximate ln(x/xo) by -(fraction distilled) whenever fd < 0.2. - 3 —aq /zjr 1f 2: l/ 5. (11) For 1—hexyne, n—C4H9CECH ———— ——> 2-hexanone, n—C4H9-CO-CH3: (a)(4) A student attempts the reaction, and is pleased that very little (side reaction) darkening occurs. S/he rapidly works up the reaction mixture but is disappointed on getting 50% recovery of starting material and no product. Explain in < 25 words why the student should have known that no product was forming. State whether a chemical test was necessary. 7“ W M £rm~ @ 14am 4 acmery VC, “if-QVW MAJ. fl ’0 7% CALM/HEM (9 (a, $041M) mm“!- (b)(4) The very reactive vinyl cation, VC, RS51CH2, involved here typically does not discriminate between strong and weak nu cleophiles. Yet in this prep, the very small amount of free water does compete well with the much higher conc of unreacted alkyne for the VC. Show electron movement for each reaction of the VC and then explain in <15 words why the VC reaction with water is much easier than with alkyne. (c)(3) After "salting out“ the product, its DCM soln contains dis- solved water and satd aq NaCl droplets, rel humidity = 76%. 0 Wh raction of the water can be removed by anhydrous NaZSO4, rh of DA/DAH = 77%? Explain and/or show calculation. 4r M «1.1 2520; 041m: («3 0,4 gnaw?) a) M WU“ @% I 1144 Aczék N1 74cm QKflW' MR UCM/“f anCf {Hf-em Nf=co 6. (6) Recall the isatin/acetophenone aldol condensation: “ CH3-C-Ph (a) (2) One of compounds above reacts ith EtzNH to form a nucleophil- ic anion. Circle the atom in the other comma which this anion attacks. ZERO if mark any other atom. (b) (4) Compound II results from the dehydration of the initial aldol product, a S—hydroxyketone. (1) Draw the structure of cpd II. (2) When II reacts with Na28204 in solution, an electronic structural change occurs. State the visual evidence of this in < 6 words. 0 (WE—Pk (1 / /@ ) \I 5’ (9 (o/or acct/£4 (om 7. (4) (a) (2) For a reaction sequence 1A a 13, 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. 7312K V3 7/- 9/14 ¥ I479 yie(6[=é§:‘x3= g QMQF g gaga ‘3 (b) (2) Does one need to know or assume anything else about the above mixtpu‘rwewgmfwwf for a valid yield calcn? Explain in < 12 words. ... a»... i. :16: M 4 “MA”: (’4 Mo 244% am. 5 1214 . WM}... 0.» mm M M “(z/:Allqfi‘lhp‘ -5- 8. (4) Consider the methyl benzoate prep as performed: M j : 8 cat H2804 PhCOOH + 30 g HOMe ~————————————a-— PhCOOMe + HOH MW = 122 MW = 32 MW = 98 MW = 136 (a)(2) If one takes 50.0 mmol benzoic acid and gets 56% conversion to the ester, calculate what mass of ester is obtained. 4M“? W4 ¢ Mat 0 ME, “6006/ f/ 6., 4 (b) (2) Calculate the ester yield as is of th ry if one recovers 15.0 We” mm (a)- 561/0 (0 0% NEW cg (2(1 1 .‘ :2 Jfiw’ ‘ Y 5% fl!” 7 “51%. 1:6" 9. (4) A and B react to form C, with Ke = 4. For initial molarities [A10 = [310 = 1, at equilibrium 1C] = 0.61, [A] = [B] = 0.39, i.e., the ratio [C]:[A] = [C]:[B] ~ 1.5. Suppose C is easy to separate from B but hard to separate from A. Calculate the equilibrium [C]:[A] for (Ala: 1 (as before), but [310: 10. In the equilibrium expression, take [C] = 1 and [B] = [B]o-1 in the term(s) not containing [A]0. Solve to get [A]eq and a new [C]e , and from these [C]:[A]. Comment on how your answer(s) show ghat using B in large excess facilitates getting a high yield (based on A) of high purity C. 3% ,4 + 6 ’1:3: C aden 9.447447 / 10 C) j_ % 14m {-x /o ->< K {/0 I I m3 2 :57 : “LLZ‘ththgéf CHZ» Gem ,6 VLC ‘WL Ami/7 (’e/WW/4/z W wax, WW ¢c W4, < 3% at. ' '6‘ /J’:=[o 10.(10) Benzaldehyde was converted to Dilantin in three steps. (a)(4) The hydroxyenamine below, E—OH, pKa~10, is an intermediate in the benzoin condensation (BC), 2 PhCHO a Ph-CO—CH(OH)—Ph, as done. At pH2512, the BC fails. Eagts: (1) If the pH is later lowered to ~10, the BC proceeds. (2) A routine by-product is a ketg tautomer of the E—OH. Write chemical reactions and structures consistent with these data “ 09 o I. f p (b)(3) For the Cu(I,II)—catalyzed oxidation of benzoin to benzil, Ph—CO-CO—Ph: Brown -N02 gas forms continuously from NH4NO3. But -N02 does not appear until nearly all benzoin has reacted. Explain this in < 25 words; show electron movement only for the reaction that actually destroys -N02_ @ 50 [may a4 have 6wedml. firwr’ 6401:.) ——" (in (ELWW‘CA r-QJMCM {‘NQJ “UL +1 ,[email protected] WW Wwflt w yml M 4L 140 what, amp-{gar}! .UOL “fl/MM/(L (c)(3) Boiling Dilantidfiz below, with conc aq NaOH hydrolyzes all carbonyl C—to—N bonds. Draw the the main organic product's structure as it exists site: mm 3:52 mi c; QXWM I / r t...» Mic-Cool! LM‘J‘T’L‘W HN NH I , cthffl4 sz é”: ...
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This note was uploaded on 07/13/2008 for the course CHEM 322AL taught by Professor Jung during the Spring '07 term at USC.

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322bf07_plq1_2_key - CHEMISTRY 322bLf325bL...

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