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322b_09fall_sample_lab_quiz2

322b_09fall_sample_lab_quiz2 - CHEMISTRY 322bL...

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Unformatted text preview: CHEMISTRY 322bL —%p!it'37'7009 -€9RSNG—%099 Z Prac‘fl‘uz. affair FIRST LAB QUIZ - F4 /( 07 BY £593 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, deduction it any part or an answer is no; resngnaixe to the question. 1. (8) (a)(6) (i)(3) (ii)(3) (b)(2) 2. (5) (a)(2) (b)(3) -1- Recall the Grignard synthesis using n—BuBr and CH3COCH3 to produce 2-methy1-2-hexanol, n-Bu-S(Me)2. H One way that iodine,12, catalyzes R-MgBr formation likely is similar to how iodide anion, I‘, catalyzes some 3N2 reactions. State the visual evidence (<5 wds) and write a balanced equa- tion for the reduction of 12 to I‘ by the first—formed R—MgBr. The I', as a Mg salt, can now convert this R-Br to R-I, which reacts faster with Mg, a R-MgI. Tell how I‘ is catalytic by writing three balanced reactions, starting with that of I‘ with R-Br. Hint: The x in "R—MgX" can exchange readily with other halide anions. 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 NH4OAc (pH~7) is better than plain water for this purpose. Recall the Pd 2 H2304-catalyzed alkylation of anisole, Ph-OMe, by Ph3C-O-é—CH3 (from Ph3COH in HOAc) to give n-MeO-C6H4CPh3. This is an example of an unusual reaction, alkylation, rather than acylation, of a nucleophile by a carboxylic ester. Explain briefly, with (a) drawing(s) if you wish, why Ph3C-0Ac with strong acid catalysis alkylates rather than acylates. Write all the products of the reaction of each of the esters below when boiled with excess CH3OH and catalytic H2304: -2- (4) Given that the rate-controlled product ratio Desired Prod to Side Prod is 100:1 at 20°, 2.5:]. at 70°, and varies exponen— tially with T change: (a) (4) Calculate the rxn T to give DP:SP a 10:1. Use care in Mining AT in the expression product ratio a some exponential function of AT. (1)) (2) If 10:1 product ratio is acceptable, tell why getting higher purity by operating at lower '1‘ might be a bad idea. For full credit, derive all values of logs from 109102 =- 0.30, e.g., 1091025 = log 100 - log 4 = 2(log 10 ~ log 2). S. (12) Recall —-) O by ‘OC1/C12 in aq HOAc. (a)(3) Write a mechanism for the oxidation step, the EZ-like attack by water on the intermediate ester, gyglg-Csfillo-Cl. Show each bond-making and -breaking step clearly. (b)(4) The reaction medium was a water-HOAc mixture. (i)(2) What is the point of using such a mixed aglyent system? Answer in <15 words. (2) Tell why aq EtOH would not work; use <10 words. (c)(5)(i)(3) Reaction of the product with excess conc aq NaHSO3 gives the cyclohexangng bisulfite addition compound, CHBAC. Write its structure and calculate its MW from the fact the cyclo- hexangl has MW - 100 and NaHSO3 has MW - 104. (ii)(2) Cyclohexangl and cyclohexangng boil within 6° of each other. Based on the work-up of the CHBAC (filtration, washing with ethanol and ether, then drying), and the tests performed on it, tell how one can get the ketone fires 9: the alcohol. Use < 30 words. -4- 6. (6) Recall the isatin/acetophenone aldol condensation: u o ca3—c-Ph (a)(2) One of compounds above reacts with EtZNH to form a nucleophil— ic anion. Circle the atom in the other oomoound which this anion attacks. ZERO if mark any other atom. (b)(4) Compound II results from the dehydration of the initial aldol product, a B-hydroxyketone. (1) Draw the structure of cpd II. (2) When II reacts with Nazszo4 in solution, an electronic structural change occurs. State the visual evidence of this in < 6 words. 7.(4)(a)(2) For a reaction sequence 1A a 15, 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. (b)(2) Does one need to know or assume anything else about the above mixture of A for a valid yield calcn? Explain in < 12 words. 9. BzOH + 30 g HOMe -——————————————a- BzOMe + HOH (b)(2) Calculate the ester yield as t of theory it one recovers 15.0 mmole unreacted PhCOOH. <2 pts if use unneeded data from (a). (c)(2) In the aq Na2C03 extraction of unreacted BzOH from DCM soln, (4) how can one tell when all the BzOH a aq 320'? Use <10 wds. A and B react to form C, with K = 3. For initial molarities [A10 . [31° . 1.0, equilibrium $8] a 0.57, [A] a [s] = 0.43; i.e., the ratio [C]:[A] = [C]:[B] ~ 1.3. C is easy to separate from A but hard to separate from B. Calculate the equilibrium ratio [C]:[B] for [AJOa 10, but leaving [310: 1. In the equilibrium expression, initially take [C]eq = 1 and [A]e a [AJO-l, leaving 1-[B]eq as the only unknown. Solve to get ?B]e , calculate a new [Cleq, and from these the equilibrium [C]:[g]. Comment on how your answer(s) show that using A in large excess facilitates getting a high yield (based on B) of high purity C. -5- 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 » Ph-CO-CH(OH)—Ph. Eagta: At pH 2 12, the BC fails. If the pH is later lowered to ~10, the BC proceeds. A routine by—product is the keno tautomer of the E¢OH. Write chemical reactions and structures consistent with these data, plus brief commentary. '3' ?” --\_ I Ph R (b)(3) For the Cu(I,II)—catalyzed oxidation of benzoin to PhCO-CO-Ph: Brown ~N02 gas forms continuously from NH4NO3. But -N02 does not appear until nearly all benzoin has reacted. Explain in <25 words; refer to reactions but chemical eqns not required. (c)(3) Boiling Dilantin(:2 below, with cone aq NaOH hydrolyzes all carbonyl C-to-N bonds while NH3 distills out. On acidifica- tion, a gas bubbles out. Draw its structure and that of the main organic product as it exists at pa = Q‘ "i ph_—iL____ifp ...
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