322bf04_plq1_2

322bf04_plq1_2 - CHEMI STRY 3 2 2bL Graded quizzes will be...

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Unformatted text preview: CHEMI STRY 3 2 2bL Graded quizzes will be available at make-up lab. -Hun-éve TAs may stay only half an hour if nobody is doing a lab. AZ 1"” ’1. (4) Recall the Grignard synthesis of 2-m yl-Z—hexanol, CH3(CH2)3C(OH)(CH3)2, from n—BuBr and acetone: CH3C0CH3. ,(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". . 7:) flow 724 (MM/M 749 Xl’gw or 3’0 (WK—W u, (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. kn) ’ to ' c‘cq “AA/é . % (J All? If $57M; mZZ‘r fir» u¢( ()0? S( ‘1. (7 )2). ~ magma? . & H w @(t M( 2- (6) Recall the Period 2 alkylation of anisole, Ph—OMe, by Ph3COH in HOAc with catalytic HZSO4 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. W ((‘M(‘[M MCLLdMM‘M . nL/w have MMWCW(¢W) p/{r (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 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, J44 I“ V‘ 91 ‘V '% Rxn 1 is Vquébmd‘b{C—, 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. C(du 00V Mcox/tvf llc, MVK futué.¢\4 JW . ‘2‘ pji=10 3. (6 pts; 2 each for (2) and (2); 3.for Lg) 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 Lagtg: (2 sig figs) the rxn rate increases for (gT = +10°. («fowav 60° Hwy/L Mm flu - £7 ficfw 071-— 7‘4' I g fad?) 2 (IV-aw) I O “at—W 4" ’f 42‘ (0", ATM+= 20°‘f F" logé = 45-103 1+ :72 263°-T= 3+°C33~%)¢(r=.+é‘ WWfir-fiwwwoa = 1+"? 3 2+” a (.7 Chm) (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. f0 slong «4’0 v»ny “2,4 14¢ fucrmfg Ira/é 4 rm 6 $er W Wind 77' W . rm )4] :9 W (“£2 firm/(From 46), (owe)! Yl‘c(l( 4A. 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/xo)]. For r = 10 calculate the fraction of the Water distilled, fdw (E 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. -l- - 25.- fi/ I ‘0“602’0 4“» “.118 am in “‘ (35;) = (014 (9.x =I(“0.7»15) ‘- 4&7, :7 64'”: 0.107 (a: 0.”) c?sz (4941955 Jig/I’M ac {244 mm : avg—1.0,} s 6’” =«M‘sré’l $6.5: w a -3. (6) For 1—hexyne, n—C H CECH -—g——> 2—hexanone, n—C H -CO—CH . (a)(2) A vinyl cation, VC, RfELCHZ, is a higher energy species than I I I g . ® ' . is an alkyl cation, AC R—CH-CH3. Yet [£3 for H + 1-hexyne --> VC is z AG for H®+ 1—hexene ——> AC. Tell what this ' means about the free energy difference between the alkyne and the alkene. Answer only THIS-questionL using <10 words. AWYH/“K‘QM’ G 61me a: VCMC cliff. (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. (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. 'h-C(=NNH2)CO—Ph (B«#, Pd 68) gave Ph-CH . = the (one—step) m- hanis for this reav o. V :0 - 6—membered ring azo tavtomer with in I a:ir electr 7' Isatin ' Acetophenone (2,3-Indolinedione) MW = 120, g = 1.03 MW = 147; mp = 193—1950 draw a line between the two carbon (a)(2) On the structures above, ther during the aldol condensation. atoms which bond to eaCh o the initial aldol product. (b)(6) (1) Draw the structure of cpd I, lely from its stoichiometric (2) Calculate the MW of cpd I so relationship to the starting materials; show calculation. %:EEEJ>— ,(3) Tell in terms of electronic structures why cpd I is white but its dehydration product, cpd II, is intensely colored. Ho aha)?!» (Mu; f as jot/«fax up \ o 4. JM‘, MIA) 5%“? ‘ (XE (+7stl267l' H 3M MW< =- (3)901 r M. “max mjugm (may; C/“Ljr A44 om. s 9.0 g crude cpd I; 3.0 g of this yields 7.4 mmole pure cpd II. (1) Calculate the yield of cpd ') cflct\ II based on isatin, as a percentage of theory. (2) If one has ‘ tting a representative sample from “41; a reliable method for ge fl crude cpd I, what additional facts, if any, must one know or lculation meaningful? Explain briefly. .(c)(4) Exactly 30 mmole isatin give assume to make the ca (05cm). flak ‘K? (fl «cm/z fMMolJ‘Mf‘ld “4% 7”“. «2: (0 “Wl‘v :3 Q?) Y(‘¢Cd => :(7Lf‘éz o/L 323$; 7% A {7% Wfl/‘c I" 130 (7. NOTHING W' A - ‘ 7 5y “(€38 km SflM_.’Lo '13 m C4 OW '5' 2‘3 3. (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, obt ains 26 mmol ester, and recov- ers 2/15 of the starting acid, calculate—— (1) the percentage of benzoic acid converted to product. .6! 6H9” = ‘W8 = 040 WA», +0 4+ 3 We 0. MM/ (b)(2) In the preparative rea ction itself, methanol played tgg roles. Name them——no descript ion needed—-in a sentence of <10 words. (M évflx Kw WWW/:4 mCMofiNHJIUM (c)(2) To recover unreacted benzoic acid, one acidified the aq Na2CO3 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? tence of <15 words suffices. rm (Mal/gob W601 One sen— ” 4W ‘ vain-Kay «OWL? XS Ufa/Cog -6- “'8. (12) PhCHO was converted to Dilantin xia 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 YECR Then show using reSonance structures why the carbanion is stabilized when ¥»‘ is the TICB shown below, but not when is 90H. ' c0. = M 5%t’fi?%‘/ 0” (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/“, sh, v3 ‘wvaf (fiOcaMI‘Mfi (MIX/4 «of pk .fv >¢:0 .[020 (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 as it exists at-pfl = Q. (The other hydrolysis products are one C02 and one NHiEDfrom each Dilantin .) ' ...
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322bf04_plq1_2 - CHEMI STRY 3 2 2bL Graded quizzes will be...

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