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322bf03_lq1_key

322bf03_lq1_key - CHEMISTRY 322bL Fall 2003 FIRST LAB QUIZ...

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Unformatted text preview: CHEMISTRY 322bL October 27, 2003 Fall 2003 FIRST LAB QUIZ By 239: NAME lgé i 1. (10)___..___ , 2l(10)_______ Lab time 3. (10)______ T.A. _ ________ 4. (12) 5. (8) 6.(12) This test comprises this sheet TOTAL (62) and six numbered pages. For questions about this quiz, see your TA first. Graded quizzes will be available at make-up lab. Mon eve begins at 6:45, Tu morning at 9:00, Wed aft at usual time, 2:00. TAs may stay only half an hour if nobody is doing a lab. 7, 3:; 42W 1. (4) Recall the Grignard synthesis of 2—me yl-2—hexanol, CH3(CH2)3C(OH)(CH3)2, from n—BuBr and acetone, CH3COCH3. .(a)(2) After the reaction starts, the mixture is diluted before continuing. In <10 words state the purpose of diluting. Be specific; zero for just "works better" or “better yield". \ \ 72’ [low flv€ 00/77/44? ({Mé),__v‘x“ (win/M 79%?“ fig 0V” 9'0 (Mu '16 we Vt t4 ) (b)(2) One must protonate the R-MgBr/acetone pr duct to get the target 3° alcohol. In view of the sensitivity of 3° alcohols cid, why not use plain water as the acid? Use <12 words. Rf? ' to (J A’pfl‘cq/f‘ 746 MM “'1qu JOMf KC % [ya/£7”? 449/. 9? “MC IC¢ hflkuf . 8‘ 4A« 2. (6) Recall the Period 2 alkylation of anisole, Ph—OMe, by Ph3COH in HOAc with catalytic H2804 to give p-MeO-C6H4—CPh3. (a)(2) This reaction is called a "Friedel-Crafts (F-C) reaction" al— though the classic F—C rxn uses R—X/A1C13. Tell in what respect the two reactions are basically similar; use <10 wds. 71"“?! W (fo/M MCLMKM‘M . Hoy- have MMWCW(QW) p” (b)(2) An intermediate from Ph3COH reacts rapidly with HOAc (rxn 1) but only slowly with Ph-O—Me (rxn 2). Yet the product after (3 one day is mostly that of rxn 2. Putting a single word in each blank below, explain how this happens under the condi— tions used: , um, .92 [it I‘V‘EL ‘V I” Rxn 1 is V1L04b¢4(b((" but rxn 2 is (c)(2) Use of toluene to recrystallize the product gives high purity material. Tell why it was not used alone; use <15 words. CHM 00v Hem/07 1%; fl‘%’ Luff fotué. :4 {“1 \ '2' pjiclo 3. (6 pts; 2 eagh for (a) and (2); 3_for (g) below). Assume reaction rates, and therefore times to 99% completion, vary exponen- tially with AT. Reaction A is 99% complete in 1 hr at 80° but takes 24 hr at 20°. (a) Calculate at what T (nearest whole degree) rxn A will take 6 hr. (b) Calculate by what (q) 00W 60" MM?» 7L‘* 1 :5? 1Ek:hv:} =3 (: - Q <¥D 1P\ 0 \o. c- I .3 G 99 y; f 0Q C> 0 0 W | (c)(2) Suppose desired rxn A competes with a side reaction, B, of higher activation energy. Explain why one might choose to run the reaction under conditions where rxn A takes 6 hr (or longer) even though one could easily run it in 1 hr. f7; and («’0 rva M “€24 1‘3 t‘Mchffi "(/6 4 new 6 why W wc‘flt 1‘7' Hm“ mm b4] :7 W (61¢ Ion/(from 16}, ((3th We“ (A. 4. (4) For the drying by distillation of solns of W dilute in an OS: Recall that for y = amt W, x = amt pot soln, and r = the vapor-to—liquid W conc ratio, the equation is ln(y/yo) = r[1n(x/x0)]. For r = 10 calculate the fraction of the Water dlfiilllgd, fdW (a 1 — (y/y0)) if one distills 20% of the solution, i.e., 1 — (x/xo) = 0.20. OK to take ln(z) = (z - 1) if/whenever |z - 1| < 0.2. 6%» 20% ((01,, szfi z-fiadw +s. {3:03 dtC 7*" (‘5. = (01.0.: =1«(“0‘2Z~3) = 4.17, =7 :16) = e‘l‘m’ = 0.107 (a: an) ail/17% «Jaw; r4 {2.4 mm) = (9.3-1.0, 7L 3 6'” WWflmrwwfl a 3. (6) For l—hexyne, n—C4H9CECH ————— > 2—hexanone, n-C4H9—CO-CH3. (a)(2) A vinyl cation, VC, Rf§LCH2, is a higher energy species than ® is an alkyl cation, AC R-CH-CH3. Yet AG for H®+ 1—hexyne --> VC is as AG for H®+ 1—hexene -—> AC. Tell what this means about the free energy difference between the alkyne and the alkene. Answer only THIS questiont using <10 words. filleu/aIK-QM G Jrfif a: vc/HC G‘lnq' (b)(2) Heating and darkening are evidence that the 1-hexyne is under- going sgme reaction with the 85% sulfuric acid. Tell what one should do to check that the desired product formed. Briefly describe the test and what constituted a positive test. Use <25 words total. ML 4 fla 06mm wrfl ALMA/M MUM. (Mow/H L/[W ,4/142—3 AW (Wm) M. Cor cm 0M (c)(2) As done, the DCM extract of the steam distillate contained some droplets of saturated brine (satd aq NaCl), relative humidity = 76%. Tell what fraction of these droplets can be removed by anhydrous Na2804, relevant rh = 77%. Give explana— tion and/or show calculation. (4) Pyrolysis of Ph-C(=NNH2)CO—Ph (BMH, Pd 68) gave Ph-CHZ—CO-Ph and N2. Write the (one—step) mechanism for this reaction: 5. H6 .., Draw BMH as the 6-membered ring azo tautomer with its :C=O H— bonded to the azo H. Then show a three-electron—pair electro- cyclic reaction giving N2 and the org prod as the enol form. ) “.H\ 0H 2] L»?! _, 'c\ + 3‘ ”7H3: c 0” ,n/ \CH » N pk / \CH t ' Nx ‘ M (0K 42/ mwm w: M391!) 3” ”(1" wa Y. Mb” 6. (12) Recall the isatin/acetophenone aldol condensation: (3 H H3-C-Ph Acetophenone Isatin ' , (2,3-Indolinedione) MW = 120, g = 1.03 MW = 147; mp = 193—1950 (a)(2) On the structures above, draw a line between the two carbon atoms which bond to each other during the aldol condensation. Circle the atom which is electrophilic in the reaction. (b)(6) (1) Draw the structure of cpd I, the initial aldol product. (2) Calculate the MW of cpd I solely from its stoichiometric lAZa ‘\ relationship to the starting materials; show calculation. C (3) Tell in terms of electronic structures why cpd I is white but its dehydration product, cpd II, is intensely colored. W Ho gutted/’1» Qi) 5044 I: w‘ jaw?“ qXXul/{L /I 0 :,L\)=w {I}: 4JMMmel’7j] H 3,14 MWg 114714745 (3)901 f [4% fife/«4X4 Gamay/4 rfflfm/r C/“Lfl: We on. (c)(4) Exactly 30 mmole isatin gives 9.0 g crude cpd I; 3.0 g of this yields 7.4 mmole pure cpd II. (1) Calculate the yield of cpd ‘) GQCLN II based on isatin, as a percentage of theory. (2) If one has a reliable method for getting a representative sample from fl‘wbiL crude cpd I, what additional facts, if any, must one know or assume to make the calculation meaningful? Explain briefly. (05cm... {WK ‘5 Oz (VKA fiMHolJMf-‘d +11% M tow/ca W..- /-,v:r:@ 0/L 3501i: VHS "‘ 3 (1 Alert-HM Mi 4 ‘ 2 6? ”“2sz 5 New 7’1 n 7:4 [1‘4 or '5' A7 298 7. (8) Recall the methyl benzoate prep as actually.done: 1 9 H2804 PhCOOH + 16 g HOMe —————————-—%>— PhCOOMe + HOH MW = 122 MW = 32 MW = 98 MW = 136 bp = 66° bp = 199° (a)(4) If one takes 4.88 g PhCOOH, obtains 26 mmol ester, and recov- ers 2/15 of the starting acid, calculate-- (1) the percentage of benzoic acid converted to product. .3: 6M4 2 ‘WS 2 040 Mm, '+ 3 We 0. me/ i 56. - 13W fifimVde +0,65% 4/ (132Cf1\l c; <:,°y(\/ MM M4 mm mm a Lg”; 0 ”pram”; [754 (b)(2) In the preparative reaction i Name them—-no description nee the yield of ester as a percentage of theory. h tself, methanol played two roles. ded——in a sentence of <10 words. 4/1 flaflx «W WW/ :1 flu (Me/{72%)511UM (c)(2) To recover unreacted benzoic acid, one acidified the aq Na2C03 extract from the acid/ester solution in DCM. Why should this process be done in a beaker many times the volume of the solution rather than in a smaller Erlenmeyer flask? One sen— tence of <15 words suffices. -6— 8. (12) PhCHO was converted to Dilantin yis benzoin and benzil. (a)(7) To dimerize PhCHO "head—to—head" to benzoin, Ph-CO-CH(OH)-Ph, a nucleophile must stabilize the carbanion (negative charge on a PhCHO (ex)-carbonyl carbon) relative to the isomeric oxyan- ion. Draw both these species resulting from nucleophilic attack by a general nucleophilic anion Yficz Then show using resonance structures why the carbanion is stabilized when ¥»’ is the TICB shown below. but not when ié is QDH. ‘ ' (O A :02 (b)(2) An a-hydroxyketone, R-CH(OH)—CO—R', is much more easily oxi- dized to a diketone than is a simple secondary alcohol to a monoketone. Explain by telling why the slow step in the oxidations is much easier in the first case than in the sec— ond. Use <20 words total. 5/0“ Site” vb .Wvo‘fflocelxéISM/I K . \—®I M mm me) \c-FO WV r ~ ' 0p £“lqm' / V "C M W (c)(3) Note the structure of Dilantin<g>below. Vigorous hydrolysis cleaves all amide/imide bonds. Write the structure of the resulting principal organic product ss it szists at pH = Q. (The other hydrolysis products are one C02 and one NHéEDfrom each Dilantin .) 9% j W flkmf”COM CGH/SCI: {O wadt’fi' ...
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