322bf07_lq1_key

322bf07_lq1_key - CHEMISTRY 322bL November 5, 2007 Fall...

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Unformatted text preview: CHEMISTRY 322bL November 5, 2007 Fall 2007 FIRST LAB QUIZ BY Rage NAME____Jt;;_15::_jrj:________ 1.(13)______ 2. (12) Lab time 3. (9) T.A. 4. (8) 5. (8) 6.(10) This test comprises this sheet TOTAL (60) and six numbered pages. For questions about this quiz, see your TA first. Graded quizzes will be available at make—up lab. Mon eve lab begins at 7:30, Tu morning at 9:30, Wed aft at usual time, 2:00. TAs may stay only half an hour if nobody is doing a lab. -1.- —— pa £-/3 1. (7) Recall the Grignard synthesis of 2—methy1-2—hexanol, CH3(CH2)3C(OH)(CH3)2, from n-BuBr and acetone, CH3COCH3. (a)(5) For the main reaction R—Br (A) + Mg 4 “R-MgBr" (B), with ratemain = kaA]. Side product R—R (SP) can arise from either (1) A and B reacting in soln with ratel = k1[A][B] and/or (2) from reaction of 2 A's on the Mg surface with ratez — k2[A]2. (i) Derive separate expressions for the rate ratios m:1 and m:2 in terms of concentrations and rate constants. (ii) If the yield of B is sensitive to [A] but not (much) to [B], tell which side rxn is important; explain in < 15 words \Slrcflr ._ in; _j #1” Z:lWng'§Lfi—i@ rd: M: "j? %= 13343 (b)(2) After aq acidic work-up, the product was extracted into ether, the soln washed, and then dried with K2003 before distilla— tion. Tell in <15 words why this drying agent was used. K10”; do bar/Jet, MM aw. W‘WJA I -r s a cox. ca hem £19m)! 2. (6) Reaction of anisole, Ph—OMe, with Ph COH in HOAc with cat. H2304 gave p-MeO-C6H4-CPh3(I) plus Side Product(s). (a)(4) Lower rxn T gives more I and less SP. Explain; consider relativelkG‘s and rxn rate sensitivity to T; use <20 words. pm *9 t A!“ [awn [AG-#1M.“ r0& .2: {Ma wn‘m 14: AT 40,.“ rag, (We :1 UM W rm (4;). (b)(2) Using toluene alone to recrystallize the product gives high purity material but low recovery. Tell what was done to get higher recovery with sl lower purity. Use <10 words. 644 ¢j~flrofi cu co-w/vewz’j —2- flj z = m, 3. (6 pts; 3 each for (a) and (b). Assume rxn rates are exponential in AT. Reaction A goes 24 times faster at 80° than at 30°. (a) Calculate at what T (nearest 0.1°) rxn A will go 4 times faster than at 30°. (b) Calculate by what Ensign (2 sig figs) the rxn rate increases for (5T = +10°. 77¢“ woe-(:1 J 304% Via/‘50)” @(Ufl =z+ >+""*ov- 9w 4. (4) or distillation of very dilute W solns, let y = amt W, x = amt pot soln, and r the constant Vap:Soln W conc ratio. Then log[(y/x)/(y0/xo)] (r-l)log(x/xo)], log to any base but the same on both sides. (x/xo) 5 (1-frac distilled). From 80.0 g soln, distillation of 20.0 9 reduces the pot W conc by 90%, i.e., Lg 0.10(yo/xo). Calculate how many more 9 soln must be distilled to get to 0.010(yo/x0). Max credit for minimum path calcn; no xalne of any logarithm needed. Fm M "fig 74- 5d," «duet w W +5 1— 67 {M 4104.0“4M'twf44571’3” :6 wwch 5. (2) For a reaction sequence: 2 A a 1 B a 1 C. If one starts with 60 mmol pure A, then takes one-half of the B produced to make I! C, calculate the adjusted theoretical yield (in mmols) of . 0 “MO faagfl-fi 5 4M ‘4(6€% 0% 30KM(,H‘1“M I we M NW C = m! ‘3‘ N12? a 6. (6) For l-hexyne, n—C4H9C2CH -—g——> 2—hexanone, n—C4H9—CO—CH3. (a)(2) A vinyl cation, VC, R5§LCH2, is a higher energy species than - <81 N is an alkyl cation, 2&3 R- —CH3. Yet 1&6 for H€}+ 1-hexyne --> VC is ~ [LG for + 1—hexene --> AC. Tell what this must mean about the free energy difference between the alkyne andv 0 % the alkene.Z Answer onlyéT:S question, using <10 worZs. “(M D v\ dlm+fl[yM FMKV'SWMF LL 9: A6.) 66"” W ,amfmwtlc'm. "'”‘ (b)(3) A student reacted 1-hexyne with cone sulfuric acid, getting rapid heating and darkening. But a 2,4—DNPH test on the rxn mixt was negative. Tell how 1—hexyne did react, in <15 words. (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 MgSO4 (rh of highest hydrate pair, '6-7W = 50%). Give explanation and/or show calculation. Aa‘ m {00%. “MM/’tm L.) mm“ WVM rm "WW? 7. (2) Regarding the Glucose PentaAcetate reaction mixture: C6H7(OH25 f d ACZO f C6H7(0Ac)5 + 5 AcOH. The catalyst, NaOAc, is initially insoluble. It dissolves when the mixture is heated, but does not precipitate on cooling. Explain this behavior, using <15 words; answer only THIS question. W a above; wC/m'f‘ ’1“! ACOHIQNMQC Maw/{1 M 5%? (U 4- mésg 8. (8) Recall the isatin/acetophenone aldol condensation: ./O C) u 0 CH3-C-Ph H Isatin Acetophenone (2,3-Indolinedione) Ml - 120, g - 1.03 m - 147; up - 193-195° (a)(2) Isatin reacts rapidly but reversibly with EtZNH to form a red- purple anion which is NOT an intermediate in the aldol conden- sation. Draw its structuzs. "a?" u ,l C nec *9 W \ “>43 m.fl‘vuc ¢ (b)(6) (1) Draw the structure of cpd I, the initial aldol product. (2) CPd I has MW = 267. Showing your work, calculate the MW of cpd II solely from the fact that it forms from cpd I by loss of one water. (3) In the reaction producing cpd II from cpd I, tell what the striking visible change meant that an extended conjugated system was forming; use <10 words. 0 gt) Ho ciao-10k CL) M603 3 W? 167’ Y 6) if" 0;! L (:3) Fem/{Hf wa/ Rod/M fly 6/0/00'6K '5‘ AZ£=Y 9. (8) Recall the methyl benzoate prep as actua y done: PhCOOH + 16 g HOMe -————————————ap- PhCOOMe + HOH MW = 122 MW = 32 MW = 98 MW = 136 bp = 66° bp = 199° (a)(4) If one takes 4.88 g PhCOOH, obtains 28 mmol ester, and recov- ers 1/8 (12.5 t) of the starting acid, calculate—- (1) the percentage of benzoic acid converted to product. (b)(2) In the reaction as done, methanol was used as both solvent and reactant. In <15 words, tell why this meant the reaction reflux required minimal attention once underway. gWKW av} woman/led?“ Meafl/ (c)(2) Unreacted PhCOOH was extracted from the DCM soln containing it and the ester with aq Na2CO3. Tell what potential hazard this involves and how it can be avoided. Use < 15 wds -6- 10. (10) PhCHO was converted to Dilantin via benzoin and benzil. (a)(5) Write a mechanism for ONLY reaction of the TICB shown below with 1 Ph-CHO to give an InterMediate HYdroxyEnamine. Draw a resonance structure of the IM showing how the (ex)carbonyl C has become nucleophilic. ..fl::) I (b)(2) Recalling how benzoin, Ph—CH(OH)-CO-Ph, differs in appearance from its oxidation product, benzil, explain why the blue—green oxidation rxn mixt became greener as the reaction progressed. mm (M 4 {flow ,4 Mimi?“ M1“? (uwfl yellow 19 Mai W #9 v QVLM' (c)(3) In the last procedure, conversion of benzil to Dilantincg? the strongly basic (aq alc NaOH) reaction mixture was filtered, liiflsL then the product was obtained by acidifying the filtrate. Draw the neutral product's structure, mark its acidic H, and some explain why this H is acidic enough to dissolve in aq NaOH. (D ...
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322bf07_lq1_key - CHEMISTRY 322bL November 5, 2007 Fall...

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