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322bsu09_lq1_key - 'Nim K EY Chem 322bL Summer 2009 LAB...

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Unformatted text preview: 'Nim; K EY Chem 322bL Summer 2009 July 16, 2009 LAB QUIZ #1 [1’7 £5 (Three pages - 30 points) 1. ( 0 Recall the Grignard synthesis of 2-methyl-2-hexanol, CH3(CH2)3C(OH)(CH3)2, from n-BuBr and acetone, CH3COCH3. (a)(2) State two phenomena one observes when a Grignard reaction, as set up in lab, starts without external heating; use <20 words. (low/«AX c.) rMi L“ K zfim¢ ELM“? (ML (5) The important side reaction in making R-MgBr from R—Br and Mg is coupling on the metal surface: 2 R—Br + Mg a R—R + MgBrZ. (b) (i)(3) Explain in terms of the rate laws for the desired and side reactions why keeping [R-Br] low as it is added minimizes the amount of side product. Use <20 words. an? mg; -.~. “{4an MW win!» fag); mé (W 45 {R 9'3 WM? trig, (ii)(2) If one starts with equimolar amounts of R-Br and Mg and 20% of the Mg remains unreacted after all the R-Br has reacted, what fraction of the R-Br was converted to R—MgBr? Give reasoning and/or calculation. OHY 60% Chat KOO/cl Lia, WK? rm mom m M? Mgfléwsthz Ma #01?» (gun—a» Erna. (c) (3) Draw the Grignard-acetone adduct and tell why after its forma— tion, one can interrupt the prep for >week without worrying about expo re to moisture or air. Use <20 words total. rem-2,3306%? . w ¢qlemf «scam? Cgiiolfifix C5? all) . fox ma" (7%, 3% {Veal/2‘4 wifl 555.5001. 2. (10) (a) (3’5 (b) (‘6 W (W) W = pt'icO ‘2‘ Recs 1 the HZSO4—catalyzed Friedel—Crafts alkylation of anisole, Ph-OMe, by Ph3C-OH in HOAc to give p-MeO-C5H4-CPh3. This acid-catalyzed alkylation also succeeds with t-Bu—OH and with 2—methyl-2-hexanol, the product of the Period 1 synthe- sis. But it fails with Me-OH, Et—OH, or i-Pr-OH. Explain in terms of the key electrophilic intermediate; use < 20 words. we? awn/(z 1:114 1:44am... W Z’agy—«mf' a Wiratafdflfl) firm VH0. Given that the rate-controlled product ratio Desired Prod to Side Prod is 50:1 at 20°, 1:1 at 80°, and varies exponentially with T change: (i) Calculate to the nearest degree the rxn T to giVe product DP:SP = 10:1. In defining (LT, be careful with signs; note that the product ratio goes up as T goes down. For full credit, do NOT use log or exponential keys on your calculator, but derive all logs from 109102 a 0.30 and the definition of a logarithmic base. (ii) Assuming a 10:1 ratio is acceptable, what adyantage is there in running the reaction at the T where DP:SP 10:1, rather than at 20°? 50% aregov‘?“ 7‘1 WIZL yry 2:179 colt 249"¢w~ué’ Laf 30° (C) (2) Recrystallization of crude p-MeO—C6H4-CPh3 from toluene alone gives high purity product. Why then was i—PrOH included in the recrystallizing solvent? Use < 15 words. QvflFO/t, m “flow " 14)!va \JUf M 5’ {W “(2%: («5% Mme? / m 0Jth _ 3 _ 0H 4. (10) Recall ---7 o by adding aq NaOCl to the H alcohol dissolved in HOAC. (4) ( (a) i)(2) Draw the structure of the key organic intermediate. (ii)(2) Explain the role of HOAc as an acid in <20 words. Consider that aq NaOCl has pH ~ 12 and that ‘OCl does not give the key intermediate. Mechanism not neces- sary but no credit for just asserting that acid reacts helps form the intermediate-—tell haw. o-ct (CC A164 Maui? 792/ 7‘7; \53 <<::::>KTF( /(:(Lf cthAa/oy- f¥yj<:;/( («Ibufcéy ' mam/5 51% +0 know [1 (0W 0H 4- + (b) (3) CycloHexanoneBisulfiteAdditionCompound is 50:. Nq Note the drawing below, showing the ketone's oxygen H-bonded to a bisulfite anion, in a specific conformation. Show a reasonable simultaneous movement of 3 pairs of electrons in a five-membered ring transition state to produce the anion of CHBAC. Draw a Lewis structure for this anion showing all bonds and unshared pairs and formal charges, except that you may draw just a bond-line cyclohexane ring. _ .. (Ext/«702‘ for Q3; w—a Q9.” c, {w " .. H . .r " M a « fig)15‘j§<£5> {? ::~fi;.*-§? VM‘d? ¢:Lt :FBV: :9; :0: {Au (ix/Zane, (c) (3) BAC's are useful because they can often be storable sources of carbonyl compounds. Write a balanced equation showing reac- tion of CHBAC with CO3= to give the ketone, HCO3‘, and some other product(s). Tell what the evidence to your eyes and/or nose what that the ketone was a product, in <10 words. 0M), 0 [trot O'V'x +5’aazéwfiij J/wfi/ , MEN/+7 Gdan- ...
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