322bs05_plq1

322bs05_plq1 - CHEMISTRY 3 2 mug-255:." W4 MW . V...

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Unformatted text preview: CHEMISTRY 3 2 mug-255:." W4 MW . V 1.(12) NAME 2 . (11) Lab time 3. (9) T.A. fld 66— 4.(1o) a “Mata-4 @(Wc gmy/QJQEUMO A0 (.04 4—3)- 6.(io) 5. (8) This test comprises this page and six numbered pages. TOTAL ( 6 0 ) If a question says to answer in fewer than a certain number of words, do so. Also, gegugtign if any part of an answer is not responsive to the question. E. i i . n . 31 t a. . r questions a ' ' , 4&3? /0C7 izlt '1‘ - 1. (6) Recall the Grignard synthesis using n—BuBr and CH3COCH3 to' produce 2-methyl—2-hexanol, n—Bu-g(Me)2. . , i, ,ir.i_lii-m Vii, H @a}(4) The Grignard rxn is a case of com i 'v - o ' rxns: RBr (A) forms RMgBr (B) with rate1 = k1[A], but A'+ B react to give worthless R—R (C) with ratez = k2[A][B]. Suppose for ‘ome value of [B], [B] iven, rate1:rate2 = 2:1, i.e., 2/3 A reacts by path 1 and 153 by path 2. If one now dilutes the rxn mixt by a factor of 3, (i) calculate what grantign of A 10W reacts by path 1, and (ii) tell in <12 words why one makes the Grignard reagent in as dilute a solution as practicable. ruAgC‘ _ .lli Cfflgz ; ‘it/ =;.;L [461/ Wt ' ill/6:63 . a 3A)“ (Hum 46‘“! ‘7 3K V3 “My +6. mfr‘o = $1? <~/7 A W W {‘7 Km 1. (3072) nae/c knife/W} W' 6. strong acid will destroy 2—Me—2—hexanol' J" 'KU. distillation. Explain why the product solution was dried with the relatively low capacity drying agent K2CO3 rather than MgSO4 before distillation. Use <15 words. K1503 ‘4 éfié‘L/l ‘ Wrdrza ‘ 2. (6) Recall the Pd 2 H2804—catalyzed alkylation o anisole, Ph-OMe, by Ph3C—OH, all in HOAc solution, to give p—MeO-C6H4CPh3. (a)(4) The desired reaction succeeds in HOAc,but fails in EtOfi,be- cause the solvent alkylation product Ph3C-O—g—CH3 easily 0 cleaves (back to) Ph3CE>with acid catalysis, but Ph3C-O—Et does NOT. Draw relevant protonated forms of the above ester and ether, including resonance structures as applicable. Then 3 explain i < 15 words, why only the ester cleaves to Ph C62 f“ 293% P” (93 ?” MK #15wa cm 4" P113 CfO'é‘me" $0: C~M< 5/2“ phaé-g-E‘t 9': WV [:VW‘ W V] out! (is ‘C‘é‘gfiififlkuiog‘m W (b)(2) Recrys allization of the product from 2—propanol gives high recovery of solid material. Why then was toluene also used as part of the recrystallizing solvent? Use < 15 words. fl/MM (folqé/(X win om'filu M w/ “17a (4 \ fléi‘f/‘Z‘ "3. (5) Given that the rate-controlled product ratio Desired Prod to Side Prod is 50:1 at 20°, 2:1 at 50°, and varies exponentially with T change: Ca1culate.the rxn T to give (a) DP:SP = 20:1, Mr and (b) DP:SP = 1:1. Use care in figflning [3T in the expres— - some exponential function of (ET. lues of logs from 109102 = f a logarithmic base.* For log 25 = log 2.5 + log 10; log 2.5 = log 10 - log 4; 2 log 2. Or wk‘u. AT: fo‘r sion rate ratio = 3 For full credit derive all va &, Adr. 0.30 and/or from the definition 0 example, ‘ 1 2 1,00 . K4,” “‘luf’ 15:1.«m lil Y1,” dwwff A For the drying by distillation of an Organic Sol ing a small amount of dissol x = total soln amt, and r = ln(x/xO) = [1/(r-1)]1n[(y/X)/(Yo/xo)]. ution contain- ved Water: For y = amt W in soln, the vapor-to—liquid W conc ratio, Taking r—1 = 20, calcu— f the solution one must Qifilill. fd, '1— 1ate what fraction 0 = 1 - (x/xo), to reduce the water concentra ion 0 1 1/20 of i ori inal value. For full credit,* and whenever |ln (a)| < 0.2 ~ L 4. (4) approximate.ln(a) by W chfc‘Xz: fojw(53 2 “ifs-0.15- {3 = -O.[Jp,‘ A67 2 _/¢A(—£)=[o.tr] ,~‘e_ L(% I fix ._/9 (510163” (A 0J4) 5. (2) A student salts out an organic from water with ordinary salt, NaCl, then extracts with DCM and separates layers. Attempts to remove aq phase droplets from the DCM soln with anhydrous NaZSO4 S ' st this mean about the PW in the system nh d SoSul/SoSul h drat compared to that of saturated tence of < 12 words. / Pa) 4~ 0A {gift/M 7 pa) $911 Md égégsf:{flfl\ Cjk, (\L1 “,1 '77 a J . . q 2-hexanone, 1;;-c4119-co-cn3 : '-6. (9) For 1—hexyne, n-C4H9CECH H2S 4 (a)(4) Rearrangement of a vinyl cation, VC, R-CH23%;CH2, to the iso i meric allyl cation, R—CH—CH=CH2, is highly favored, i.e., a very exergonic process‘g9 Yet its rate is negligible here, and usually. Explain in terms_of orbital overlap with a marked 1% \ ' on» / CK Ha. } H W717 TI" oréfie . ‘M 51402, or f 634’ “(AKA Hfl W! ~ ’L\ or M/w 9 2 57% WW4?" “M V‘ (,4 / p v M at t? f . ‘ Wt 4 (it Which ) a“ I 014% (b) (3) To make a case that the W AG‘s for the protona- . tions of 1-hexene and 1—hexyne are about equal, it_was argued that their rates of protonation were about the same: Explain applies here. why this correlation of rates with zysoverall Recall that these protonations are highly endergonic and what 's means about the relationship between the transition state Answer THIS QUESTION ONLY, not one from the and product. a non-responsive reply. .—_————-——_ practice tests--NET negative score for M" smffivs :2 AMW. *5 .. 'évcwmié‘ AG fl V Wyn/u: PKM, m [314 g (WNW ,oer LS Efrem- (thAJL,) &"s. L“; 2244_JZAL€?/€? ‘ (c)(2) A student decides to hurry the reaction along by increasing the acid conc from 85% to 95%. S/he gets rapid heating and darkening, and all the alkyne reacts quickly. Yet a 2,4—DNPH test for ketone is negative. Explain in < 15 words. {HA 7N!) 4&4 We? W“! / MQCWMMM‘ Waflwmf 1:24-10 -.7. (6) Recall the isétin/acetophenone aldol condensation: C) H cn3—-ce-Ph '.Isatin ‘ Acetophenone' '(2,3'Indolinedione) MW = 120, g s 1.03 =MW s 147; mp =_193-1$5° (a)(2) Circle the cpd above which gives a red anion with EtzNH. This anion is NOT an intermediate in the aldol condensation. (b)(4) Compound 11 results from the dehydration of the initial aldol product, a B-hydroxyketone. (1) Draw the structure of cpd III, the product of adding 2 H's to compound II. (2) Calcu— L\ late III's MW solely from its relationship to the above start- fil~JZRC ing materials. flout I (Ht’g'lok ' ) M“) t as U r spit-gNa/fl 7.(4)(a)(2) For a reaction sequence 1A a 1B, A limiting: 'Exactly 60 mmol A is in 125 mL aq solution. From 50 mL, one obtains 15 mmol pure B. Calculate the % yield of B based on A. _, 13’“ ‘ ' “LY? ’ a; '5 (67/570 o); gfceam) (b)(2) It is certain that the 50 mL sample above is representative. Explain why this is so, referring to definitions of terms; use 1< firms/.4 % a, m,» a P» ‘W”“’ M WW W m. ‘ 22% '8. (6) Consider the methyl benzoate prep as perforAder I cat H2804 PhCOOH + 30 g HOMe -——————-——==,— PhCOOMe + HQH MW = 122 MW = 32 MW = 98 MW = 136 ' (a)(2) If one takes 60.0 mmol benzoic acid and gets 65% conversion to the ester, calculate what mass of ester is obtained. MM ,0er = “max/MIX 6:26 - " (b)(2) From (a), calculate the-yield of ester as a percentage of theory if 13.33% (2/15) of the PhCOOH is recovered. (c)(2) The extraction of PhCOOH from DC With aq Na2C 3 is easy to follow visually but can also be hazardous. Explain BOTH these facts using a chemical equation and < 12 words. 44 MM M‘Wfl a?” cavél v add “,2 9,4» Mm «7’64! “4f “57‘ 9. (2) State two properties common to MeOH and EtOH that make them easy to separate from most of their esters even when the alcohols are used in large excess to make the esters. 'l /M 5460”: M“ M240 .. 10.(10) Benzaldehyde was converted to Dilantin in three steps. (a)(5) A catalyst for the benzoin condensation must convert PhCHO to a species in which the carbonyl C is nucleophilic. Write a mechanism for reaction of the_TICB below and PhCHO going ONLY ‘ to this species; name it and draw two resonance structures. " Pk‘C‘H i-—-r . iii? (b)(2) There are several visual signs during the oxidation of benzoin to benzil. One is that the blue-green solution becomes green— er. Explain why this occurs. Hint: Keep your explanation simple; recall what the color difference is between benzoin and benzil. Use < 12 words. 5w..- ha " 5M 4gb) M, g/mefiww ra/a gNQW/L. (‘ .4 k d (6 wt try-ele "(c)(3) Closely related to the benzil a Dilantinc3>rearrangement is the reaction below. Write a mechanism. h ’ V . (#:41— 9 0 2H ph-c—d-H + EbH ---- ——> Ph- H-coc53 L2 “6 o@ I ...
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322bs05_plq1 - CHEMISTRY 3 2 mug-255:.&amp;quot; W4 MW . V...

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