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spring11samplelabexam1blank - CHEMISTRY #1 prq FIRST QUIZ...

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Unformatted text preview: CHEMISTRY #1 prq FIRST QUIZ ring BY Eflgfi (jibe, 6 5V NAME Lab time 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, dedugtigg if any part of an answer is an; W to the question- ve tests April 8 — 13 at make—up labs-—may be there only fir alf hour-—and 0 Morning labs convene at 9:00 a. 5 about this quiz, please see (7) (a) (4) (b) (3) (5)- (a)(3) (b)(2) .1.. Recall the Grignard synthesis using n~BuBr and CH3COCH3 to produce 2-methyl-2-hexanol, n-Bu~g(Me)2. H In preparing the Grignard, Billy Bonehead rapidly 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. NOT connected with (a) above: Suppose the target product is 2«bromo-2~methylhexane. With a chemical equation and <12 words, tell how to get this 3° halide in a one-pot operation from the n~BuMgBr«plus-acetone bromomagnesium salt. Recall the 82304-catalyzed rxn of 30 mmol anisole, Ph~OMe, with 4 mmol Ph3C-OH in HOAc soln, giving p-MeO—C6H4-CPh3. In HOAc soln containing as little as 10 mmol EtOH the rxn fails, even using presformed Ph3C-OAC plus H2804. Explain, using chem eqn(s) and < 20 words; mechanism NOT required. After pouring the rxn mixt into water, suction filtration gave a gummy semi—solid. Washing with ether left a crystalline solid. Tell what the ether washed easy (<6 words); note which W—insoluble reactant was in large excess. “2.. (5) Given that the rate~controlled product ratio Desired Prod to (3) (3) 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:SP : 100:1, and (b) DP:SP : 20:1. Use care in deiining (XT in the expres~ sion rate ratio = some exponential function of A§T. OK to derive all log values from logloz : 0.30. You may solve part (b) "in your head" by recognizing the pattern of the numbers 5, 20, and 80, explaining briefily. 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 actizatign energy, Eact; use <15 words. DiChlorMethane (DCM) has nbp = 40°. It can be easily freed of dissglxed 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- 0 6- (9) Recall OHHW by90c1/c12 in aq HOAC. (a)(4) Write a mechanism for only the iozmatien of the intermediate ester, gzng~CSH1lO«Cl. Show each bond~making and ~breaking step clearly; regard this reaction as a nucleophilic attack by oyclohexanol on C12 followed by H+ removal by water. Then explain why this alkyl hypochlorite decomposes rapidly to a ketone but tebutyl hypochlorite, Me3C*O~Cl, does not. (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 axgided by having the rxn mixt nearly neutral. Draw the structure of this (non)~product. (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. 7. (2,3-Indolinedionc) us a 147; mp ~ 193-195o (a)(3) (b)(3) (c)(2) (2) - 4 i (8) Recall the isatin/acetophenone aldol condensation: »»0 (3 u "*0 CH3“C-*Ph Isatin AcetOPhenonc M" t 120. g - 1.03 Draw a line between the two C's which bond to each other in this reaction and circle the nucleophilic one. 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. Treatment of the red soln of Compound II with M323204 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 molecular structure. For a reaction sequence 1A a 18: mL aq solution. pure B. Exactly 50 mmol A is in 100 From 30 mL of the soln, one obtains 10.5 mmol Calculate the % yield of B based on A. - 5 l 9. (7) Consider the methyl henzoate prep as perfiormed: cat H2804 MW e 122 MW 2 32 MW 2 98 MW e 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 grama PhCOOH one should take. (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. 10.(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. ’/ C:‘\;(>. - 5 - 10.(9) Ph~CHO was converted to Dilantin via benzoin, Ph*CH(OH)~CO~Ph, and benzil, Ph-CO~CO~Ph. (a)(3) The oxidation of benzoin to henzil. Ph~c~g~Ph, involves a catalytic oxidant and a stoichiometric one: Rxn(1): Cu(II) oxidizes benzoin to henzil while giving Cu(I). Rxn(2): NH4NO3 oxidizes Cu(l) 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 worde. Do this question ONLY. (b)(3) Rxn(l) is in fact two one-electron steps. 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) » Cu(I) is already shown. \ ./.0" ® (2 ‘\7 E H Cu l . .I 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: a my all: ,0 a -c-c: W,- __ .. P!“ g o NdOH,bozl fl"? é O OH ...
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This note was uploaded on 03/15/2012 for the course CHEM 322BL taught by Professor Singer during the Spring '07 term at USC.

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spring11samplelabexam1blank - CHEMISTRY #1 prq FIRST QUIZ...

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