322a lab quiz 2 fall 05 key

322a lab quiz 2 fall 05 key - CHEMISTRY 322aL/325aL...

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Unformatted text preview: CHEMISTRY 322aL/325aL November 30, 2005 FALL 2005 SECOND LAB QUIZ BY 2393 < E NAME 1.(10) 2. (6) Lab time 3. (8) T.A. 4.(11) TOTAL (35) This test comprises this sheet If told to use less than a certain nuMber of words in and four numbered pages. an answer, DO SO-—deduction for excessive verbiage. ELEAfiE EDIE; Graded quizzes will be available from TAs Thu and Fri, Dec 1 and 2, at (check-out) labs and office hours ("special" office hours for TAs with no lab or regular office hours Thu or Fri). If you initial here ---- ——> , your quiz will be put in the Study Room, SGM 102, at 5 p.m., Fri, Dec 2. All quizzes will be thrown out Jan 29. ELEAL EXAM is Thu, Dec 8, 8:00 — 10:00 a.m.: F - Q in SGM 123, R - Z SGM 124 (as before); A - E in SGM 101 (fig; THH 301). ‘1' “(9 2=/O 1. (10) Dehydration of 4-methyl-2-pentanol, (CH3)C H(OH)CH3, as done produces the following methylpentenes (MP8) without skeletal rearrangement: 4-Me-1, 4-Me-2, 2-Me-1, and 2-Me-2. (a)(3) Different isomeric compositions arise from 60% aqueous H2304 compared to 70% acid. While an ion's absolute rearrangement rate is the same in each solution, one gets a smaller fraction of rearranged products from the 60% acid. Reconcile these facts using <25 words; limit your answer to THIS QUESTION. Mia/flax du‘a/ (41 mm, Act/40¢ :é HM» fl 4 M M'fl NaWVCUL ~ Sign/(f Carédcaj“ 47W {t‘fifi‘is 7:? Ff W W [oraaéu/fq . (b)(4) The portion of the MP GC to the right shows 2-Me-1 and 2—Me-2. (1) Draw the ion which can directly form 2—Me-2, but no; 2—Me-1. (2) Assume the GC shows the equilibrium mixture. On this basis alone, tell which peak, A or B, is 2-Me-1; justify your answer in <12 words. @ u? @bth-g/CHLCH; (f m) , 7—@0¢ l’M—e'lwbm S2.) M {vac/f W W Jujvfif‘tf’é/ auflnVQS/J] gnaw. o; W #wmg (c)(3) Total methylpentene yields in this prep are typically 20% — 60%. The side products are dimers and higher polymers of the methylpentenes; from 70% acid, these may be the main products. However, the methylpentene samples usually had little or none of these high MW materials in them. Referring to step(s) in Jc‘flefl lo (11% m Wé hi7 A14 C9, [444‘ VO/a/{Lz'{< a; . WC/L (WM/L V/Ocs —:»; 5 via/OWL «WI/t Alt/Jr aim 5”. ' 2 ‘ i Q 2. (6) Note the gas chromatogram of the commercial went, "Skelly B". 1 -—-I I III-Il—I' l...- m l—II' l ' fl—l ' I “=- fiVgllI-J—mgfll=--I- —I—II_Il_-- I‘ll-III...” ‘1' Ju— m-r null-lint.- -——-—---—I—I—— 4w 5. Ila" l-Ill— "- —-I—n—llll—II—Il— I I ‘1 I- .- “mu-“unl- mn—Ifl-Ill-l-ll- [I IQ“.- mill-I'll“ a “Mun—“mil -III—III .— Ill-Ill“ —_—— =I—-—ll x ——-_—l _- I. -\=-—= I. I Bosehne (a)(2) Which peak is associated with the component of highest vola- tility? Number -IL (b) (4) Recall that one estimates the areas of GC peaks by assuming they are triangular and calculating “Kb-h". Using the base- line indicated, mark peak 3 to show how this is done, drawing the height and ash, then determine the area, in "squarelets" . Also state how one Meanings Kb, using < 12 words. -3- 3. (19 pts total, 8 pts on this page) ’QJ7 fii " E? In the last experiment, Period 10, you studied the bromine- catalyzed isomerization of I, cis-X—CH=CH—X (X = COOMe) to the trans isomer, III. The bromine—containing species, II—gauche and II—anti, are intermediates. (a)(2) Recalling the behavior of the two reaction mixtures containing 73:2, write a reasonable initié?ionstep for the reaction. 6” (12’3" (b)(4) Using the framework below, draw the more stable conformation of the radical ~CH—-CH-Br, the key intermediate in the I a III I I X X transformation. Show the mechanism by which this radi— cal turns into III, assuming that Br- is the chain—carrying species. Use a "fishhook“,\\__’;r, to show movement of a {B r single electron. (c)(2) Compound I, the starting material is a liquid; III is a solid. Maximum yield of III requires enough Brz that 4%—10% of I gives solid dibromide by—products. For ease of purification, tell why one might use less Brz, accepting a lower yield of III and leaving some I unreacted. Use < 25 words. 50314,, 5am [(7:48 f _\ [await/mg: “HULK/VI} w \ flick/W QM W/oaw‘fy. / '4‘ Mir—II 3. (concl, 11 pts on this page) (d)(4) Given that 128 mg Br2 (MW = 160) reacts with 24.0 mmol I (MW = 144), 60% of I a 111, and all the Brz reacts by adding to I: (1) Calculate the mass of III formed, and (2) calculate the mole ratio of III to Br—containing product(s). @M(‘)MWEZ '3 ' M ..——~l___________——_————_————-—-Tzzgr”_—-—_—-‘ 1’ ‘_q> .====.r:3E:"‘ 2— , C? "((2ch "UM gr (60% [0 2 MM/ ,fuén :3? OXVKW/ 8r~mhcw fry—9% ch“’*(-(e)(4) Suppose the I a III Kequilib in i , = l, and that the main driving force for the reaction is the crystallization (xtln) of III. This amounts to viewing the reaction as two steps: I a supercooled liquid III (IIISCl) » Illcrys. «J (1) At ~l4°, zysxtln = —1835 cal. Taking RT = 570 cal, use .AG = -RT ln thln to calculate K. (2) If IIIscl forms an ideal soln, calculate III's solubility as its mole fraction. «A (335‘ @4 WKvafi 6. 7"; - e_ $70 :: 25:0 4. (3) A substance A's solubility in a solvent 3 is 30 mole %, i.e., mole frac A, XA = molesA/(total moles in solnb = 0.30. Calcu— late how many mmols of A will dissolve in 175 mmol S. W(I4+-l7f Tag? 1374 ofimmfikrffl—45fi” 40M ‘ 7/ 2 {75” M _ WMMR m 3 m 9 MWW' ' 7r ...
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This note was uploaded on 10/06/2009 for the course CHEM 322A taught by Professor Singer during the Spring '08 term at USC.

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322a lab quiz 2 fall 05 key - CHEMISTRY 322aL/325aL...

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