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spring98-MT2-exam

spring98-MT2-exam - (ll(l(ll-f Chemistry 3A Spring 1998...

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Unformatted text preview: (ll((l(((((((ll((((((((((-f((((((((((((((((( Chemistry 3A - Spring 1998 Midterm Exam # 2 Professor Jean Fréchet Your full signatuflwwmwh & we April 7, 1998 Print your full name ngi , Marissa, go’mei (Last name, First name, Middle) Your SID BBSRSQB Please check the section number and name of your GSIIT A. _111 DeForest,Sarah _311 DeForesLSarah 121 Berseth,PolIy _321 Keet,Corinne 131 Richards,$teven ___331 Ponte,Maya 141 Yamamoto,Kana 341 Seymour,Sean 151 Brennan,Paul '__351 Werkema,Evan 211 Esker,Todd _411 Esker,Todd _221 Kriesel,Josh ____421 Peters,Eric ___231 Zylstra,Eric _431 Freeman,Adam 361 Liang,Scott _511 Liang,Scott 371 Paisner,Sara _521 Magliery,Thomas 381 Kim,ESther ’ ____531 Kwon,David 391 Bise,Ryan _541 Winans,Katherine 551 Janes,Jeff If you are making up an I-grade, indicate the semester Do Not Write in this Box, you took 3A and the Professor ' This exam has 9 pages; make sure that you have them all. We will only grade answers that are in the designated spaces. Please do your scratch work on the backs of the exam pages. Write only one answer to each problem; multiple answers will receive no credit, even if one of them is correct. N_og This examination runs for a total of 80 minutes. No questions will be answered by proctors after the exam begins. Please write Iegibly; ambiguous or messy answers will receive no credit. © 1998 J.M.J. Fre'chet. Berkeley. CA Chem. 3A ‘4, Midterm Exam #2 Page 2 of 9 e ‘ I 1. (12 points) ' a J (a) Draw a Fisher projection of J (28,3R)-2-chloro-3methylhexane ~’ H‘- 9°) ‘4 M J (L (s) (b) Name the following compound: HZCH3 ' ‘ . U n J (Use IUPAC nomenclature and do not H" ..... 1' ltb'dicl‘iixo Fir? 11m.— " forget stereochemistry) C C Cl .- I f5 ”,2 b 4 (c) An old bottle of 2-iodobutane has a label marked "2-lodobutane mixture of _, enantiomers". The optical rotation at of a solution of 0.089 of this mixture in 2 mL of J solvent measured in a 5 cm tube is found to be +0.192°. Given that the specific rotation of pure (R)—2—iodobutane is [a]D = -16°, What is the optical purity of the sample? Calculate the percentages of (S) and (R) enantiomers in the old bottle. Show the equation " used for the calculation of [a]D as well as the details of your calculation. 5 b 1 kq/w ‘ s. ' 1;— 0.08 / .5:— 0.OLl —' ' 0C0 SENE"; _/' mead whim ‘5 final. {film}, [CL] = _______... _ semi ldm ,. O , a, V b , (Wilfslltl‘nnflwlf. lDO/W‘ ”3 m x\\/\—/"\-—/”‘“\~———--J \W__._-m.fi_m_‘mew: 0. W20 2+? L00 m(33”2*L'O{iOlDUiW[_°L:l -—— +lU: in (W i ” MIR ‘J + loo: O.Loxl00'~' So [000/0 Capture (53 v “FWD 0 0 ' emu/veto. 4 ‘ (lo/owes) “0" “t 0‘ 80% [is (s) e 0PM“) ~ (900/0 boo CR) " purity J 7a x \ 1A x \ : Answers: Optical Purity= [900/0 ’F‘WE'CS) % (S)= 2130A: % (R): (310040 : ((((((((((((((l(((-((({((((-((((lll((l(((‘((( ( Chem. 3A Midterm Exam #2 Page 3 of 9 (0)2. ( 10 points) \.’ (a) Circle any molecule below that has an (R) configuration according to the Cahn—ingoId-Prelog convention (b) What is the observed reaction rate for the 8N2 reaction below given the following concentrations: [CH3Cl] = 0.5 mol L"; [OH'] = 0.03 mol L'1 and the rate constant k = 0.003 mor1 L 3". Your answer should show an equation for the rate law as well as all calculations. CH3Cl + 0H9 —> CH30H + one (x .\ . . — ) mic: IJL[CH5Cl1 [OH 1:} 1'?” E z“ < if“, ' L5: ‘ Ml {mg-g; u» 0, 005 mol” L'SflKLOKJ mol' L—JLO'DE Moi L :i 3 pool. 5. )1 L. .. - -\ -' HUBXIO 5‘ twel'sl'L «kl «e l ' ANSWER Rate: H.5xl0'5 moi-3“'L'l (c) Circle any compound below that is optically active CH3 H Br H3O H H30 H H Br CH3 411938 Chem. 3A Midterm Exam #2 Page 4 0f 9 / - e/ 3. (14 points) (3) Explain why treatment of (S)-2-iodooctane with Nal causes the optical activity of ‘ @e starting material to disappear. Your answer must name and describe in one sentence the type of " eaction mechanism involved and its stereochemical consequences and show a complete equation s/ 4 a.) ‘4’ with__all m‘aterials (starting and final) and their stereochemistry.{2—iodooctane is CHacHI(CH2)50H3) \ I .x ‘9 ““‘ + MT / 1 ,e , tutti-”M“ (s)— 2-Eodnoo-tw //’ e“ A ' hf" . r" "- ff ‘0 ‘\’ V. “x 4 CS} ’2 ~ L octave-tam “1/” (F0- 2 — COCLOOU’ OLYLL (”I N . W/M/fi‘MMWW—sm 3;” ,m ,__.....~--—~~-r- - . J Ob SN 2 mm W chasm-“meg, trove .1ng11; J (b) Propose a step-by step synthesis otCH30H=CHCH3 from ethanol as the only source of c atoms. Show all reagents required for each step but no mechanisms or curved arrows are needed. 4 r" y s \ o .PBf *\ M5 3 k ,. 4s, /‘\ ._____._..,, Aw Br « ’\ 0H 13"” Mixer “3 D O “t Poe A \‘A B sh Hso it 4 OH CH s0"; H + P N H10 MN J 2. H / H20 4- \ ‘fl J -t l J J J ‘4’ J -./ k ((l((((((((((fl((((((((l(((((((l((l(((((((( Chem. 3A Midterm Exam #2 Page 5 of 9 @4. ( 10 points) (a) Show the most favorable conformation (as a SAWHORSE projection) of the starting material for the E2 elimination below cmcm Hi9“ fl... ch—c=CH-CHZCH3 WC H cwcm CH20H3 R Br h C ”J/ H3,- \L/ Y \ 0142053 (b) Show a clear stereochemical representation of the alkene produced in this reaction. (0) Write clear structures for the products containing no oxygen atom that are formed when LE 2-bromo—2-methylbutane is allowed to react with excess warm potassium t-butoxide. ‘\ CH CH w . "ma Cl H\ _'_..:ICHZCH3 K9 t‘BUOe H \ / 2 3 W /C\ ——> c = C 3' CH3 A H / \ H H, YE!‘ / OH H CH3 /CH3, x‘x/HCHZCH?) 3 \ C t C/ "DY " /C =- C\ H Y H / W H __ H Cissé'l’rows {Samara bisthfefiug-Ehng WWMM‘ “7+ 03 Chem. 3A Midterm Exam #2 Page 6 of 9 5. (12 points) 4 J % (a) How many stereoisomers are possible in principle for the compound shown below (circle one number) V, h. ll 2 4 6 8 2 c *1 OH Ail-but? Lemme/84 3‘ ‘K CH 3 9 27 ‘r-M'L‘JE n :4 "6 3‘ CH3 3 J V H0 “ H OH 18 20 24 32 Br . 4 LJZDW E”! ‘l i 36 48 64 81 " 9 lo J @ Rank the following nucleophiles in order of reactivity for an 3N2 reaction I] e “’ H20 HS C2H506 0'6 J ‘—-/ ’ H] .__ ED . _.. ANSWER: H30 > C2 H50 > Clo > H20 4 Most reactive Least reactive ‘" I Lo _. a v . . . . Csz (c) Explain why the free-radical monobromlnatlon of ‘4 affords a racemic mixture. Show the structure of HM" 031.17 a both products and the intermediate leading to them H3C v,- (Structure of intermediate F Structure of products ’N J ~_/ 7/ "’ J J v_/ Brief Explanation: a racemic mixture is obtained because... L +14% ‘5 - ' ’ 0.01 ' tic/thy. . whim mm L IS Mu cud filmed}. um. W W ! —{ 4mm: MW%W.WW. W, 5.07., rgmts; W W SOD/o 5% the U2.) Wow. we wamu m1 8 NOW/We W- How 1’ : 592 W -=-) mam mdadmgtfi Chem. 3A ~i l S Midterm Exam #2 Page 7 of 9 6. (15 points) (a) Show clear structures for all of the products normally expected in the reaction below. Assume that no rearrangement occurs and do not show any mechanism. In H O B 90H i-L NH CH3 + H20 2 2? ‘\ 8H ‘5 c-‘ob 5 4 (a H c 3 Jr I OH +, 3: H30. Sui SM H" OH H H 7”! 5 2- ‘r, \ CH" I; 1L I v1 "I v 3 H5O 4 + 4 -'r a E E i E r (b) What is the order of the reaction? 8 \ ANSWER: Order of reaction = i + I N (c) Show a complete step-by-step mechanism (show all curved arrows!) for the reaction beiow +3 Br {((((((((((((({(((((((((¢(((( rrrr : Ca ‘5; J‘— p j + it) +1 or? ((f(((((‘,{_ ( Chem. 3A Midterm Exam #2 Page 8 of 9 7. ( 12 points) (a) Which of the two synthetic routes, A or B, shown below would be best to obtain a high yield of the desired product? Explain your answer discussing briefly the type of mechanism involved and comparing the species in each reaction. Also show a clear structure for the side-product that might be obtained by the less desirable route. I G CH30 + 0/ \ OCH3 0/ + le KKLKKKRKLKKK e o - (1M wwebwiuem com E) LA CL '3 WWW“ m OK ”H a? tum. «ex/1M Cuxci. (my 3’. mi Jrluz MCII’UleU -' Biz/Wet; 1 as :5 on? cmdt mitt} W. emblem, sci/u" MWM M turf M . our _, SN We; flea W”? V "ctbua t3°c£D«-l‘£-&N%WWI 67*.- Eft'wvé‘fé .33: CH. owia 0L. fifrm c; lag/OAK dun. ' Wm. Ar Gob.“ Midweek-t" le... (Pd-x. ' . O . - j ' v .4 E . ' '1' ‘1 LL { 10: g, gambit}. {:12 Wwwu uClALOKL P/LO‘OLutLt 7 Mbuflree “l b.5— 4 K A “ 9‘ . - '7‘: p. 4. , - .__J LydLé (:3 fist. Mutt-“J Wot , ‘nge—nr } L.» M “Hep. by “if Low} +5 xLCCuC/L..+i~€_ [stew “ ._/ Answer: " Answer: Structure of '4 side-product J Best route to product for less .4 desirable route A. k a_/ J (b) Complete the reactions betow showing a clear structure breach of the missing reagent(s). i J J CH3CHZCH20H cr-racnzcuzm o n/ \J J o cmcnzcnzon 0&0“ch J t L. ( (((((((‘((|(((_fl,.fal_‘((((((.((((((((((((((l(((((-(( .\ Chem. 3A Midterm Exam #2 Page 9 of 9 8. ('fiQaints) Show the structure of the major product(s) obtained in each of the foliowing reactions. Your answer must show clear stereochemistry where applicable, write NR if no reaction occurs. Do not show any mechanisms! H v ‘ crasse H A -__. ----—'->' 1 l H . D' Br Acetone H595 u I +3 CI CH‘CHa A ____ 1‘ 0 no am ' nowaims itadmafim CH3cooe NV ROLMMLH 'H - Br in CHaCOOH 3.3% 0; 61436.00 Prquf-f; _. 'WmlLWi mfikb wilt-9“ ' TsO MAJ-x: pyridine ,5 N R \- h made. "i’sCi +0 «Form 3 J’DWQEEQ J’Wt $03” 0 O ”A O/vD” +3 2) H+IH20 © 1998 J.M.J‘ Fréchet. Berkeley. CA ,q4J¢J¢J_¢Jq¢v/dqv¢dd¢4vVJJHdJ¢¢JJ¢QJ,JJJ¢¢J ...
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