spring11samplelabexam1key

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Unformatted text preview: This test comprises this page and six numbered pages. IOTAL (60) If a question says to answer in fewer than a certain number of words, do so. Also, dgdnggign if any part of an answer is as; {sangnsixs to the question. ril 8 - f 2. (7) (a)(4) (b)(3) .’ .\ ,flr Aid“ atom/r £13.... (5) (a)(3) (b)(2) «1.. is {‘1 Recall the Grignard synthesis using anuBr a d CH3COCH3 to produce 2~methylw2~hexanol, n~Bu~ (Me)2. H In preparing the Grignard, Billy Bonehead rapidl adds 67 mmol n«Bu-Br to an equimolar amount of Mg metal in ether. Only half the Mg dissolves; BB is willing to accept a 50% yield of Grignard. But he gets no reaction with acetone, and work up gives a hydrocarbon which has no functionality. Write chemi» cal equations showing what happened. Explain why consumption of halt the Mg gave a net yield of zero Grignard reagent. GUM £34 on , 30 W M GH‘yum/fl NOT connected with (a) above: Suppose the target product is 2~bromo~2amethylhexane. With a chemical equation and <12 words, tell how to get this 3° halide in a one- ot o era ' from the n~BuMgBr-plus~acetone bromomagnesium salt. 4(C, AQch AJAX}er tic/g our/A WK ] k (1"fgCZQ ’6)!” é/w Recall -~ H2804-catalyzed rxn of 30 mmol anisole, Ph‘OMe, with Ph3C~OH in HOAC soln, giving p~MeO~C6H4~CPh3. In HOAc soln containing as little as EtOH the rxn fails, even using pre~formed Ph3C-0Ac plus H2804. Explain, using chem eqn(s) and < 20 words; mechanism NOT required. mega we macefiswwfl? #300 W 695/ ~ 66 6 Miriam/We suction filtration gave After pouring the rxn mixt into water, a gummy semi—solid. Washing with ether left a crystalline solid. Tell what the ether washed away (<6 words); note which W-insoluble reactant was in large excess. {EKWJ com ‘ om war/9M W67~ [7 (016Qd5j7 N“ #2. pg ra/f 3. (5) Given that the rate~controlled product ratio Desired Prod to Side Prod is 80:1 at 20°, 5:1 at 60°, and varies exponentially with T change: Calculate the rxn T to give (a) DP:S? : 100:1, and (h) DP:SP a 20:1. Use care in deiining (1T in the expres. sion rate ratio a some exponential function of [1T. OK to derive all log values from logloz a 0.30. You may solve part (b) "in your head” by recognizing the pattern of the numbers 5, 20, and 80, explaining briefly. C4,) WM rm? 2 5(/é 6;” [Araéo~T) $04" .. 4.01” 2 { ’vflm’.) { (cno ‘" ,sflm / [6’+'[ \fy @“OS‘”“M oval? We 7%? 1:. “PC/‘1»b0”) 9A3: aka: 4. (3) Among kinetically competing reactions, the one which involves the breaking of fewer bonds is often favored by lower T. Correlate this with the T sensitivity of a reaction's rate to its activation energy, Eact; use <15 words. film mfik few/"flu? h T“ MW mfl @53/amm f“ ea. 5. (3) DiChlorMethane (DCM) has nbp = 40°. It can be easily freed of dissolved Water simply by distilling a portion of it; This is because the vapor from a W-in—DCM soln has a W cone 9 times that of the solution. The W solubility in DCM is ~0.17 wt %. Explain why it is desirable to remove any W droplets from DCM before drying by distillation, but an inefficient drying agent is good enough. Use <20 words. .3.‘ A] ‘11-? 0H 6. (9) Recall H --—.- ObYQOCI/Clg in aq HOAc. (a)(4) Write a mechanism for only the fiozmatign of the intermediate ester, cyng»C6HIlO«Cl. Show each bondwmaking and «breaking step clearly; regard this reaction as a nucleophilic attack by cyclohexanol on C12 followed by H+ removal by water. Then explain why this alkyl hypochlorite decomposes rapidly to a ketone but t-butyl hypochlorite, Me3C—O~Cl, does not. é‘fl (" j “a .. <3” C Va Q/§*\+ a H .. g tho" 040%] If" 43 d6) (b)(3) During the addition of aq NaOCl to cyclohexanol in water~HOAc, the pH is never far from 7. Tell what acid~ or base~catalyzed reaction of cyclohexanone with a substance in the reaction mixture is largely aygidgd by having the rxn mixt nearly neutral. Draw the structure of this (non)-product. \ w ‘ “4&3 w 7‘7» 0-10 co QWQQZZZZZMWO/“Q/ 07 5% fi/W WW m A at MW) {330 (c)(2) Tell what evidence from your reactions of the cyclohexanone bisulfite addition compound (CHBAC) indicates that it readily turns back into cyclohexanone by reaction with either acid or base. Answer using <20 words. 5/de m; M0 30% //% eat/L (WM/9% , ragga éaag fl M '4‘ ZmIO 7. (8) Recall the isatin/acetophenone aldol condensation: gavaQ??g tfl (I'M Cédfl‘ Ct)” Isatin Acotophononc (2,3-Indolincdione) MW - 120, g a 1.03 MN - 147; up - 193-1950 (a)(3) Draw a line between the two C's which bond to each other in this reaction and circle the nucleophilic 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. ' P 51"”! t / flow/(r, hf Q} V Wlww/ "3/ W [134,142, c)» dado/ZN/e/ (c)(2) Treatment of the red soln of Compound II with Na28204 resulted in rapid fading of its color. In <10 words, tell what this means regarding a change in electronic structure. You need not refer to, or even know, II's structur . A@¢WQ4WM M3 56w?“ (fly/flax . 8. (2) For a reaction sequence 1A a 18: Exactly 50 mmol A is in 100 mL aq solution. From 30 mL of the soln, one obtains 10.5 mmol pure 8. Calculate the % yield of B based on A. 4M? 6) M 4 51/“ “if “M/ X. 43? =_ ifmmf 33%).?65/2 % M 2: 9. (6’ Consider the methyl benzoate prep as performed: cat 32804 PhCQOH + 30 g HOMe -~__“uw.~.. PhCOOMe + HOH MW a 122 MW 3 32 MW a 98 MW 2 136 (a)(2) If one needs to get 60.0 mmol methyl benzoate in a hurry and has a procedure which will give at least 40% conversion of the acid, calculate how many gtama PhCOOH one should take. ALQQI éfl7xC)VK‘“fiI fi:;:i::é: :; {4‘3 ¢,4,puu¢/ ‘0 M 0+ W 16%? ' // 3"- [flmwjhw (b)(2) Calculate the % yield if in fact one got 52% conversion and recovered 20% (1/5) of the starting acid. At most 1 point if use unnecessary information from (a). (c)(2) Using chemical equations and <15 words, explain how unreacted PhCOOH and PhCOOMe, both in DCM soln, were cleanly separated from each other. PM“ we napoQMfi U 10.(3) Write a balanced equation for the conversion of glucose C6H7O(OH)5, MW 2 180, to its pentaacetate by rxn with Aczo. Calculate the product’s MW; Ac— has FW 43. 7/ w Qéoagéflr + {/4130 ‘M Qd‘pwflclf' inf/£624 5/0 3% 300 N t5“ 1;? 10.(9) Ph«CHO was converted to Dilantin via benzoxn. Ph~CH(OH)~CO~Ph, and benzil, PthO«CO~Ph. 0 fl (a)(3) The oxidation of henzoin to benzil, Ph-§~C«Ph, involves a catalytic oxidant and a stoichiometric one: Rxn(1): CuCII) oxidizes benzoin to benzil while giving Cu(l). Rxn(2): NH4N03 oxidizes Cu(I) hack to Cu(II) while getting reduced to water and N2. In this rxn mixt, Cu(II} is blue~green, Cu(I) i9 light tan. Based on the solution’s color at reflux. tell which rxn contains the slow step; give your reasoning in < 20 words. Do thin question ONLY. (b)(3) Rxn(1) is in fact two one-electron ateps. The first step likely involves the structure below, a Cu(II) complex of the enediol mono-anion of benzoin. Show a reasonable series of hgmglytic bond cleavages giving a neutral organic radical and a Cu(I). The reduction of Cu(II) a Cu(I) is already shown. \C’C'?‘ (9 \C‘0 + @517 CLL ( C I a .f H (c)(3) The reaction of benzil + urea in aq alc base —-> Dilantin is similar to that of the oldest known organic molecular rear« rangement. Write a mechanism for the reaction below: FL 0 t - -1: flq d‘c ‘ a W5 \9 mow”): th§“é"0 0” 0H /JL\ ph~c~c-§5= ——~—————=» Ph‘f“C\ ‘ ‘ ‘. . OH O OH 9'6 ...
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