CHEM-1 - _1_ (4) Recall the Grignard synthesis using...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 4
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 6
Background image of page 7
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: _1_ (4) Recall the Grignard synthesis using n—BuBr and CH3COCH3 to produce 2—methyl-2—hexanol, n—Bu—g(Me)2. H (a)(2) Once the Grignard rxn starts, one dilutes, and then adds RBr soln. Finish this sentence, stating a behavior in <7 words: One adds soln slowly enough that the reaction mixture—— 20mm and (LOIOV 04L dim/PW 7< (0 (b)(2) On addition of an acid HA, the intermediate bromomagnesium salt gi es the target alcohol, Mg+2 ion, and the conjugate base, A , of the acid. Any acid with Ka 2 10'16 will produce the alcohol. To avoid a difficult work—up separation, tell what property A§>should have (or not have). Be specific regarding an interaction of A‘, but use < 12 words. a, QhUWd “07L be» a 0064/6 @066. X U 2. (6) Recall the Pd 2 HZSO4—catalyzed alkylation of anisole, Ph—OMe, by Ph3C—OH, all in HOAc solution, to give p—MeO—C6H4CPh3. (a)(3) Whether one usesggggg or Eggs as solvent, the initial rapid reaction is alkylation of the solvent by Ph3C+. Write the structures of both the neutral alkylation products, one from HOAc and the other from EtOH. ;/ ,.,r K 1/929 i (EM/7’ /" Wrap/p IDA’C’FA .My/dfr‘q’ I. / >, PA [h In a few days to a week, one gets much alkylated anisole from the HOAc rxn mixt but NOT from the one with EtOH. Tell what this must mean about a difference in behavior between the two products of (a) and how this accounts for the difference in results for the two reaction mixtures. fl (rf“ The Mommy: mom Occws“ hamper, Hofic and Pig H reve‘v‘g’ibsaso during “49 (NUS *0 0‘ W9“! W039 “nae aach '70 be aflkg/lot‘fed. The macho‘vx bemweem ROM and mac? ls \RKEVEKQBLE. (b)(3) n 3. (9) Given that the rate—controlled product ratio Desired Prod to Side Prod is 40:1 at 20°, 1:1 at 60°, and varies exponentially with T change: (a)(3) Calculate the rxn T to give DP:SP = 4:1. Use care in defining [3T in the expression rate ratio = some exponential function onEF. (b)(3) Calculate the rxn T to give rr = 100. For full credit derive all values of logs from 109102 = 0.30 and/or from the definition of a logarithmic base. . “' ‘ A v 1 CI) 30° Amara": . b) “9063 7 47‘ y: CIA, I [0946) ’4“) [0961’ /0C’ 5' , 7//7 // igvgoo £1.44” "/05‘7 /fj/w"47/‘7'7 , 7 [’1 H oi “: é L} r? a: : J‘f/ ’,0q0 V fré? v~: ,gy :zflf / . 97/7 4 O i ' (c)(3) Circle the correct choice in each set of choices separated by a slash ( / ): One would be inclined to run the reaction at the hioh-a emperature if the cost of starting materials is high / {Ky , th- :paration of pure DP from the DP—SP mixture is 2Q, and thof the reaction proc— i essing equipment per u time is / low. x 4. (4) For the evaporation of dilute aq ammonia: For y = amt NH3 in soln, x = total soln amt, 556 r = the vapor—to—liquid NH3 conc ratio, ln(x/xo) = [1/(r—1)]1n[(y/x)/(yo/xo)]. Taking r—1 for ammonia water = 13, calculate the conc of NH3 (wt %) in a . r. _ solution originally 4 wt % NH3, after 10.0% of the solution irfimfiwh9¥N¢5 has evaporated. For full credit, approximate ln(x/x0) by yo (,Sfifi‘ —(fraction distilled) whenever fd < 0.2. *1 .- \D: hw‘DNH- 2:: 3-)r - 1:5 2; /X'— WaH‘W r; «o (H w) w 5 X0 X: WW? mi, 0{' soln. XOIWVTIKQWl-fifi WM -: 1‘“, ‘ Io 'us'ahs "i p . Wigwam” k W asmarmfl/fl / If Vilof‘c "4.3577: f . €4,367? 5L Kg :2 Wm, MIN :2 m4; 2 5. (10) For l—hexyne, n—C4H9CECH — — — — ——> 2—hexanone, n-C4H9—CO—CH3: (a)(3) Explain the following fact(s) in < 20 words: If one gets heating and (side reaction) darkening when carryingwoutythe L.._,M___ WW, ,._, m____ above reaction, one may:6rvm§y,n9t be producinngshexanone. not producing the desired ketone. Considéf'that the desirgd and side reactions have a common intermediate. Bit"“"‘i‘f:massage..slerkeningI Dilemmas surely (b)(5) A vinyl cation, VC, R—E=CH , is a very reactive electrophile, which typically daésmfiat iscriminate between strong and weak nucleophiles. Yet in this prep, the specific rate of reaction (i.e., the rate adjusted for (nucleophile the vc with watgr‘is very—finch greater than thatmwithwunreact— wwwwconcentration) 6f ‘ed alkyne. Show the electron movement for each reaction of t e VC and then state in élS”woidsWWhy the specific reaction rate With”a1kyné”istmfitfi lower than that with water.” ANSWER THIS QUESTIONMONLY, not one from a practicé”EEStT You could get a NET NEGATIVE score here for a non—responsive answer. ~H H. Q f7)“ OH 1‘ \06 I I ___————% “J ea R-CILOHR fZ-C533C+42 Rafe i9 lower WM] 51,1“;me beau“ gag/er “+17 brgdk (weaker bang/j, (c)(2) After "salting out" the product, its solution in DCM contains a little dissolved water, plus some droplets of saturated brine (satd aq NaCl), relative humidity = 76%. State what fraction of these droplets can be removed by anhydrous M9804, relevant rh = 50%. Give explanation and/or show calculation. Brim will 528 removal w fang ad I75“ MIME? pfés'fliré is 67wa W“ m Mire» firm/1 42m 0f DCM, An Hm O bf/IILL wi/l £96 90/16,, «iv/tar) H Wamihfi parfnw PhQSS‘i/Wj, of Mgf’oy, 3 6. (8) Recall the isatin/acetophenone aldol condensation: R 0 CH3-C-Ph l H Isatin Acetophenone (2,3—Indolinedione) MW = 120, g = 1.03 MW = 147; mp = 193—1950 (a)(2) One of compounds above reacts with EtZNH to form a nucleophil— ic intermediate. Draw this nucleophile's structure in the form which correlates with its nucleophilicity at carbon. 0 / Q -_ , , ll . a e are? ~- 04% (b)(6) Compound II results from the dehydration of the initial aldol product, a B—hydroxyketone. (1) Draw the structure of cpd II. (2) Calculate II's MW solely from its relationship to the above starting materials. (3) In the reaction of II with Na28204, what is the evidence that an extended conjugated system is being destroyed? Be brief but specific. . H v. ‘ y a! / Z Q67 ' WU color in form wok/fefoa/orzgn) I ) [>0 Lug/CM», 7. (2) For a reaction sequence 1A a 1B, A limiting: Exactly 60 mmol A is in 150 mL aq solution. From 50 mL, one obtains 15 mmol pure B. Calculate the % yield of B based on A. (6; 8. (6) Consider the methyl benzoate prep as performed: cat H2804 PhCOOH + 30 g HOMe ————-——————€>— PhCOOMe + HOH MW = 122 MW = 32 MW = 98 MW = 136 (a)(2) If one takes 50.0 mmol benzoic acid and gets 65% conversion to the ester, calculate what mass of ester is obtained. (b)(2) From (a), calculate the yield of ester as a percentage of theory for recovery of 18.75% (3/16) of the PhCOOH. 33?i§'rnrno/ ./ / $10! 6525/ 52? m 8/“. (c)(2) Tell why aq NaZCO3 extracts PhCOOH but not the ester from a DCM soln. Use one or two sentences with < 25 words total. TM WW I! paw of 7%? Wyclmc I772); re och/5L Ph 000/-/ [s palm" elf agowaws; ’ 9. (2) C and D react to form E, with Ke z 4. E is easy to separate from C but hard to separate frong. If C dissolves D and has a suitable bp, why might using C as both reactant and solvent largely solve the separation problem? Use <20 words. 0 + Djva 05mg (3 m sac/o 6m €XCFJJ‘ a/‘lawr all/"J D in rm 61'“ #7: (WM 5 =~-w’r» : ,2 -6- f)’ lO.(10) Benzaldehyde was converted to Dilantin in three steps. (a)(4) Write a mechanism for ONLY the reaction of the species below, an intermediapg_inmghe thiamine—catalyzed benzoin condensa- tion, with (another; ____ 3:15:30 to form benm Z912/11. > «Tmfi V....,_r f7? (1 Show proton transfer(s) intramolecularly. Pk CQF:H O OH n ”“ - " 5%? 9491:6567 PW ‘w i? S 231+ C ‘ by I. g :0? OH I 22%? avgww 42;; new ——> 9 PJ R my Ph 1' ¢’ Ofl . . g /? I R n/ ? K H (b)(3) In the PhCHO-to—benzoin reaction, addition of aq NaOH to the thiamine-HCl solution gives the bright yellow ylid/carbene TICB, the actual catalyst. On adding Ph-CHO, the color fades somewhat. When reaction is complete, the soln's color deepens again. Explain the fading and then re-deepening of the color in terms of how and why the TICB conc changes. Use <35 words. (c)(3) Benzoin was oxidized to benzil, Ph—CO—CO—Ph, by excess NH4NO3 with catalytic Cu(I,II) in HOAc/W. N02 is produced by decomp of NH4NO3 during the reaction; N02 does not itself react with benzoin. But only when the benzoin is nearly all oxidized does N02 appear. Explain the series of reactions which con— sume NO2 before this. You may, but do not have to, write the reactions themselves. No.7 (is axidlzeai bag CHI, 80 HdOE’S HM WWW”. #0 9M WW) I Q/oprV (I N051 m £07m 06 gag; Pl? 7 ll. (9) In the Wolff—Kishner—like reduction of benzil (structure on previous page in part (c)), it was converted to its monohydra— zone, Ph—CO—(C=NNH2)—Ph (BMH). On heating in 1,2—ethanediol, BMH decomposes, giving Ph—CO—CHZ-Ph, the Desired Product. (a)(3) Write a balanced chemical equation for the decomposition of BMH to the ketone DP and another substance. From this, tell what the reaction's driving force is, using <12 words. —-———-' H C ., - ,« - =. . n ,_ . fl); “"9 Fh/ \Cfb—Ph 4 Nz/Vg Th€ el€v11ro (gain/11y 07f . /-C\(%;Nii\}fiq N Came flu; acf'zoh (*0 “a Mam/7. (b)(3) The reactive form of BMH is an intramolecularly H—bonded azo tautomer of BMH. Write its structure. .fisg/(4 [{ N: ,,—C‘\.C‘7 Ph (c)(3) The yellow color of the reaction solution is that of a side product (SP) from reaction of BMH with Desired Product): (1) DP (2) DP + Both reactions are irreversible. Assume rxn (1)'s rate is proportional to [BMH], and rxn (2)'s rate is proportional to [BMH][DP]. Explain why running the reaction at lower initial conc of benzil will result in a better yield of DP ultimately. You may consider a definite example: Compare the relative rates of the two reactions for an initial BMH conc [BMH]O and then for [BMH]0 n/10. H [‘BMI-Ilo:\ vg. [BMH]G: n, . 3’3. 'WQ W higher (Vii/1H]. mum p12; mm [W] 1w @421 a m” ( \ X 232: 9. =m+e3 wi‘fix tower (BMHJG 4M mt wwid w X ' ...
View Full Document

Page1 / 7

CHEM-1 - _1_ (4) Recall the Grignard synthesis using...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online