322bs08_lq1_key

322bs08_lq1_key - CHEMISTRY 322bL/325bL April 9, 2008...

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Unformatted text preview: CHEMISTRY 322bL/325bL April 9, 2008 SPRING 2008 FIRST LAB QUIZ [ET_}// BY 239$ NAME_—K_—_ 1. (12)— 2. (9) Lab time 3. (9) T.A. 4.(1o) 5.(10) This test comprises this page 6.(10) and six numbered pages. TOTAL (60) If a question says to answer in fewer than a certain number of words, do so. Also, deduction if any part of an answer is not responsixe to the question. TAs will have tests April 10 — 15 at make-up labs--may be there only first half hour--and office hours. Morning labs convene at 9:00 a.m. For questions about this quiz, please see your TA first. 1. 2. ‘1' (7) Recall the Grignard synthesis using n—BuBr and CH3COCH3 to produce 2-methyl-2—hexanol, n-Bu- (Me)2. H (a)(4) For the main reaction R-Br(A) + Mg a "R-MgBr"(B), with ratemain = kmlA]. Side product R-R can arise from either (1) A and B reacting in soln with rate1 = k1[A][B] and/or 2) from reaction of 2 A's on the Mg surface with rate2 = k2[A] . Suppose one finds that rapid addition of A gives much coupling even initially, but that adding A to a soln of B iltered from Mg also forms (more) R-R. Circle one choice in each set: This mean; that the impor- rxn(2) ® neither. neither during the rxn to maximize the yield of Grignard reagent. tant side rxn(s) is/are rxn(1) Therefore, one should keep a low conc of (b)(3) Suppose the target product is a mixture of 2—Me-1— and 2—Me-2- hexene, bp ~ 95°, steam distills at T <75°, gives some poly- merization with conc strong acid—-recall the Methylpentene prep. In <20 words, tell how to get this alkene mixture in one Operation from the n—BuMgBr-plus—acetone salt. P ‘ .fi ‘ Lfvy fir mlaln/OLA'I‘k, MW} 541/) «a a 4$sa+£éflnxmfilx M, 3 “~le M'o‘AfiZ/ “W 6/412 (5) Recall the HZSO4-catalyzed rxn of 30 mmol anisole, Ph-OMe, with 4 mmol Ph3C-OH in HOAc soln, giving p-MeO-C6H4-CPh3. R In HOAc soln containing as little as EtOH the rxn fails, even using pre-formed Ph3C—0Ac p us 2804. Explain, using chem eqn(s) and < 20 words; mechanism NOT required. (a)(3) (b)(2) After pouring the rxn mixt into water, a gummy semi-solid. solid. suction filtration gave Washing with ether left a crystalline Tell what the ether washed away (<6 words); note which W—insol reactant was in large excess. Mk C pk‘o M?) _2_/\g-\ fljig? 3. (5) Given that the rate-controlled product ratio Desired Prod to Side Prod is 100:1 at 20°, 5:1 at 60°, and varies exponential— ly with T change: Calculate the rxn T to give (a) DP:SP = 200:1, and (b) DP:SP = 10:1. Use care in defiining (3T in the expression rate ratio = some exponential function of (5T. ' L>> For full credit derive all log values from 109102 = 0.30. (E;amples: lo 20 = log 2.0 + log 10; log 5 = log 10 - log 2; log 4 = log 2 = 2 log 2. log1010 = 1 by defn. @pr= 50.0 AT= 60°“7’@ Asa/r = $310310 + /00‘1§= 3:01:03) +0.7 4. (4) For the drying by distillation of an Organic Solution contain- ing a small amount of dissolved Water: For y = amt W in soln, x = total soln amt, and r = the vapor-to-liquid W conc ratio, 1n(x/xo) [1/(r—1)]1n[(Y/X)/(Y9/x°)]. Taking r-1 = 10, calcu— late what fraction of the solution one must distill, fd, = 1 - (x/xo), to reduce the water cone to 2% of its original value. For full credit, take ln 10 = 2.3, ln 2 = 0.7, and pproximate (1 - a) by -ln(a) whenever |ln (a)| < 0.3S.{r——- Mir/7 5. 9 For 1—hex e, n—C H CECH —————ib 2-hexanone, n-C H —CO-CH : ( ) Y“ 4 9 H2304 4 9 3 (a)(4) With regard to some high energy intermediates, an argument was made that rates of formation correlate with [XGform. In <25 ’\££“({ words, give the chain of reasoning, with the aid of a drawing. Do not just name the principle; say what it is. 9006- *: 5¢y H gr» AG Fm .117, W W: nt. 6 AG? V‘va'fih 5 P1“ waf‘ @kw‘ WW AGfijGQVW@ mmwm w W506? Mfl AG? 6L1 005% AGQrm. (b)(3) Write a mechanism for the rxn below. Show each bond-breaking and -making step distinctly, and draw relevant resonance '- 6)“: structures. Take H3O+ and H20 as the relevanE acid and base. ‘?'H cat H3O+ '8‘ R-C=CH2 ————) R-C-CH3 &W U W K‘C“ 4: <-——“-,€- C.“ CH: (c)(2) To get good product yield, it is better to start with acid too weak to give a reasonable rxn rate and add conc acid than to start with acid too strong and dilute it if the mixture heats and darkens too rapidly. Explain why, using < 20 words. '4' fijZ‘lO 6. (8) Recall the isatin/acetophenone aldol condensation: Isatin Acetophenone r A (2,3-Indolinedione) Mu - 120, g - 1.03 o!- uc 14w - 147,- mp - 193-195° ‘\ (a)(3) Draw a line between the two C's which bond to each other in this reaction and circle the electrophilic one. (b)(3) EtZNH was the (basic) catalyst for this reaction. But stu— dents who used too much got pretty purple solutions but no product. Explain; use (a) chemical eqn(s) and < 20 words. (c)(2) Treatment of the red soln of Compound II with Na25204 resulted in rapid fading of its color. In <10 words, tell what this means regarding a change in olootxonio structure. You need not refer to, or even know, II's moloonlar structure. A... 5.2% @6025? 7. (2) For a reaction sequence 1A a 1B: Exactly 100 mmol A is in 175 mL aq solution. From 75 mL of the soln, one obtains 27 mmol pure B. Calculate the % yield of B based on A. ,7 22/0 8. (7) Consider the methyl benzoate prep as performed: cat H2804 PhCOOH + 30 g HOMe ————3- PhCOOMe + HOH MW = 122 MW = 32 MW = 98 MW = 136 (a)(2) If one needs to get 80.0 mmol methyl benzoate in a hurry and has a procedure which will give at least 40% conversion of the acid, calculate how many grams PhCOOH one should take. 0% __ 20.0 Maud MW 2/424 WI 6%flt/ M — m a :- Mfimwd mm 1d” 7m"??? O‘ZOMI X %}f: (b)(3) Calculate the % yield if in fact one got 60% conversion and recovered 20% (1/5) of the starting acid. At most 1 point if use unnecessary information from (a). 0% “1’0 Yie[c( = W “mm M swam/4% : 5”le 2E] (c)(2) The DCM soln of the ester was only superficially dried before distillation. At a pot temperature as low as 100°, water might decompose the ester, bp = 198-200°. Tell using <15 words why water attack on the ester did not occur. fl “(wjnJ/ 41% U [WI/0361 Ml 6651/. 9. (3) Write a balanced equation for the conversion of glucose C6H7O(OH)5, MW = 180, to its pentaacetate by rxn with Aczo. Calculate the product's MW; Ac- has FW = 43. Ki) (cléggMW/Jr + S/v’ch—eCa/waflc) ./ +§ a “Ow/{smog 4° N @ +§K+3w Miwo 10. (10) Ph—CHO was converted to Dilantin®in three steps. (a)(4) A pH >8 but <11 is essential to the thiamine—catalyzed benzoin condensation. Acidic impurities are a common problem. (i)(2) What gas in air reacts with PhCHO to form an acid? Ow, 0!— OKY7e/V‘ (ii)(2) The rxn mixture had 30 mmol Ph—CHO, 3.0 mmol thiamine (as thiazolium ion), and ~2.5 mmol NaOH. Explain why if even 10% Ph-CHO a acid, the rxn mixt pH becomes < 7; use < 15 words. (0% 4 Mama. 3Mw/. 7MM/ Kwfl W flaw Malafl, 1,5’Mm/ “40/; =§ /°/7L47, O O (b)(3) The oxidation of benzoin to benzil, Ph-g-g—Ph, involves a catalytic oxidant and a stoichiometric one: Rxn(1): Cu(II) oxidizes benzoin to benzil while giving Cu(I). Rxn(2): NH4NO3 oxidizes Cu(I) back to Cu(II) while getting reduced to water and N2. In this rxn mixt, Cu(II) is blue-green, Cu(I) is light tan. Based on the solution's color at reflux, tell which rxn contains the slow step; give your reasoning in < 20 words. Do Lhifi question ONLY. W 'VML Rxmfl) CaCflAMW/‘h—9QCQbMyfl W4 Mix/Lng Cq(f)rNH7IUU3’—964an‘u/L an goat; Solq a)“ 46 ,_ f‘ 5a VB 4 :3 /M7L(V¥M 'L) fiijlaJ7 Cvmti. -==;> Mu C!) W rags (c)(3) After refluxing the Dilantin rxn mixture, it was gravity filtered. Where was the desired product, and why (<15 words)? A:::> Tell how the solid product was obtained, in < 7 words. (MM-aw a w; fi/i‘mfi 41¢ {/11 Qwssoo “Q (411‘ Mk x) 6mm W'KILW. @606 If «C(‘a’vfx‘jf ...
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This note was uploaded on 04/25/2008 for the course CHEM 322BL taught by Professor Singer during the Spring '07 term at USC.

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322bs08_lq1_key - CHEMISTRY 322bL/325bL April 9, 2008...

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