Exam_Three_1_Answers

Exam_Three_1_Answers - WEDNESDAY NAME 1 1:30 —:20 PM LAST...

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Unformatted text preview: WEDNESDAY. JULY 16, 2008 NAME _ _ 1 1:30 — [:20 PM LAST NAME GIVEN NAME ID NUMBER SC CHEM 2020 6.0 Organic Chemistry Third Examination, Professor Michael G. Organ The exam consists of] questions on Q pages. Please make sure that your copy is complete before you begin. The points for each question are given at the beginning of the question in parentheses. QM the answers written in the space indicated will be considered for marks. If you write beyond the space allocated, you will be deducted at least 1 to 2 marks from the total for your answer. An extra piece of paper has been included for you to use to rough out your answers Questions requesting explanations MUST be done in full proper sentence form. Answers filled out in pencil will NOT be considered for reegrading. DO NOT pull exam pages apart; if pages go missing you will receive zero for those missing pages. n Points IA PERIODIC TABLE OF THE ELEMENTS WA 0 9012 I 1 ' . _ "" I .1 40.03 44.95 47.00 50.042 51.900 54.930 53.93 53.70 53.546 37 30 39 40 41 42 as 44 45 46 Rb Sr Y Zr Nb Mo Tc R Fth Pd 35.47 37.02 03.91 91.22 92.9 95.04 (98) 101.07 102.9 106.4 55 7 11 Ba r 1:17:13 0 22 22603 E; WE ..- C)th a“ .4 55 . 57 7 73 74 75 6 7 C5 La Hf Ta W Re 05 | Pt 132.91 . 1.38.9 1713.49 180.95 1 3.55 136.2 190.2 192. 195.09 : = : 9 1 4 1 I 1 6 10 I ' Fr 'EAc Unq Unp Unh Uns I [223] . 227.06 (251) (262) (263 ' Lanthanlde Series : ' -I - - - o' 6 ES 6 68 69 70 71 Ce Pr Nd Gd Tb Dy Ho Er Trn Yb Lu 1413.12 “0.9 14d.2d 157.25 156.9 162.50 164.93 167.26 168.93 173.114 175.0 masses shown here are 1977 TActlnide Series IUPAC values 90 91 92 93 94 95 96 97 90 99 100 101 102 103 ' Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 232.0-1 231.04 236.03 237.05 24-1 243 2-37 2-37 251 252 257 258 259 250 Note: Atomic l. (a) (8 points) Are the following compounds, in whole or in pan. aromatic, anti-aromatic, or non—aromatic. Place your answer on the space provided below the structure. if} ..(-) . -‘ (+) Cl(-) Na(+) \~.~>C\ ,— fl ‘ — N N 5/7,. l4 \=/ = Wax/7f? 4 "' X '- - r,_li. 1/1 .' . {I - 'u__ 'I tarry/inf .lr / Ll) (b) (4 points) Consider reactions (1) and (2) below where sodium hydride (base) is being used to deprotonate acids 5 and 7: kid-Lu ” -)Na + H H N H H ( H 5 6 H H (2) OH L ©"(')Na(+) +H2 i. Which reaction (i.e., l or 2) occurs more spontaneously? l Why? ii. Which acid Ge. 5 0r 7) has a LOWER pKa value? 3 Explain , If - ' l ‘ "7 \' M;%sgi1l_li'z_l1_)jl2/ l6 14A A? a (To get any points above for i and ii, you must have a reasonable explanation; stand—alone guesses receive zero) 2. (9 points) Cousider the following pairs of isomers. Using the spectroscopic method indicated (underlined), describe how you could differentiate between the three pairs of isomers: (a) Mass spectrometry: Be specific and include the masses of the molecular pieces from any fragmentation or elimination that you refer to in your description. You only need to refer to ole fragmentation or ole elimination, but it should be expected to be a major one in the spectrum. You may also use a drawing beside the structures, or even on the structures themselves, to illustrate your answer if you feel that would help. (b) Infrared spectrosco lR : Make reference to specific absorptions (stretches) in the Spectra of both compounds; give wavenumbers that you would expect (approximately) for the absorptions being eluded to in your description. You only need to describe one difference for full marks. 0 O (c) “C (Carlyn Nuclear Magnetic Resonance spectroscopy Llflt’lRI You are given a sample of each of compound 13 and 14 shown below; using carbon NMR spectroscopy how would you differentiate between these two compounds - with no ambiguities what—sieve; (be very specific). 3. (24 points) Complete the following sequences by filling in the missing reagents and/or organic compounds (starting materials or products). If stereochemistry and/or regioehemislry is relevant, be sure to include it. (a) O s t , 7 i”) u} Sfl/ 45.. (b) («fox ‘ o. W I J 1. M90 Br2 ’ ll ’ in ether 02N FeBr3 1' ’6;— ——————)- Q —~ at ‘F OCH:3 H CH3 major product 3. H”: H20 . W . | .. to tum/t 8-" -' v it w \ 3ft? ‘2 ' (C) \ up ' ~ 00 l ‘7 b 9} OH ' f \ add H’r in ."H I 7 Br / ‘KH- l I, (1 equw) 'Vm U previous mixture ether . ,. . solvent \5 - (d) 4. (20 points total) (a) (5 points) Give a detailed mechanism (i.e., including curved arrows) for the formation of AHESS]fllJlERODUCTSfrom the reaction of ethylmagnesium bromide with cyclohepteneoxide shown below. Be sure to label all of the species, including intermediates, and point out any stabilization factors that may be operative. If resonance structures are possible, draw them all out for every possible product. Show all information in the space provided. /—- t fl ‘ x '_-,'/" _I_| \ . a. H f “a J f, -“\\ r 1. CHQCHgMgBr / x I I 1 2 Ii 2- ; ‘III ' ' M j! OVKJ' . l'r-L/L— if 2 ' W “J, 'l— a: K..— 1 \ f" . . . . . . . . 5 ' ) (b) (l pomt) What IS the stereochemistry at C1 (i.e., R or S) in the starting material? "’ _ J E III } (c) (1 point) What is the stereochemistry at C2 (i.e., R or S) in the starting material? (d) (1 point) ls/are the product(s) that you have drawn a chiral molecule(s)? 6 Ell-NJ AIL i (e) (2 point) Would you expect that the product (or product mixture if more than one product c0uld be formed) to rotaeplane—polarizedlight? Explain ’ I F -- Zt/“g % gifiéng-{3933 g. :'gt-£gv_<-_g_.__r (f) (3 points) Does this reaction illustrate any aspect of stereospecificty? If so, what is it and how does it originate — explain FULLY? Place your written answer in only the lines provided below. If you feel it would help, you may refer to your mechanism above. but it is not necessary. , {_ (f) (3 points) Does this reaction illustrate any aspect of regioselectivity? If so, what is it and how does it originate — explain FULLY? Place your written answer in only the lines provided below. If you feel it would help, you may / ' f \x _/I (“fa-T: MEI/f? ' J 4'1 ._ .. T_._._ refer to your mechanism above, but it is not necessary. . J f t g) (4 points) On the reaction coordinate diagram below, draw the profile for firefliflstep of the reaction 1;qu (i.e., involving ethyl magnesium bromide) energetically including all starting materials, any and all reactive intermediates and transition states, and prodncts for the MAJOR product of this reaction (if more than one product is possible). Draw the actual chemical structures on the diagram itself, in addition to the reaction curve(s). Although the energy levels are relative (not absolute), there should be a clear distinction between the energy levels of the species listed above that would account for any selectivity demonstrated by this transformation. Ambiguous answers will receive no marks. PE Reaction Coordinate 6 5. (10 points total) An unknown compound showed two molecular ion peak in its’ mass spectrum at I98 and 200 We (see next page). The 'H (proton) NMR and protonidecoupled 13C (carbon) NMR spectra, along with the IR spectrum for the compound are also shown below. On each nme draw ole—arlx and My parts of the unknown structure, molecular bits and pieces, which can be gleaned from important signals in each spectrum for part marks. Be clear what spectral signals are responsible for the structure that you have drawn (ambiguous answers get zero). Place the structure of the unknown compound in the box provided at the end of the question. (2 points) 'H (Proton) N MR Spectrum: a] inf—1.5: "Eh-2U U :'-':-.(./ - flu 't"{.f;.._.=-.e’./f;- I a: lb.“ In“... r “flu/J Solvent CDCl 3 (Q5 Cont’d) (2 points) Infrared Spectrum: moo man do: moo (2 points) Mass Spectrum: Rclalivc Intensity 50 100 150 200 [71/6 (2 points) Unknown Compound ANSWER ALL OF THIS QUESTION, THE CORRECT FINAL STRUCTURE IS ONLY WORTH 2 POINTS 8 “Do EITHER Question 621 OR 6b, do NOT do bothM 6a. (10 points) Synthesize the target indicated using only 3fiethylpentane (shown) and any inorganic reagents necessary in the most efficient route possible. All important intennediates should be drawn out, however, mechanistic details are not necessary. /)/\ plus any inorganic reagents you require /:\|(O} ‘ ‘ OH t it”? 71)) / /]¥ I r 11 ff /\x‘i"/MIR \ / l i; / / F71) fi I Lil/— “fix MDo EITHER Question 6a OR 6b, do NOT do both”: 6b. (10 points) Prepare the target indicated using benzene (shown), any twoecarbon starting material of your choice and any inorganic reagents necessary in the most efficient route possible. All important intermediates VG? should be drawn out, however, mechanistic details are not. necessary. ,0 + as many two-carbon units of your choice as you need plus any inorganic reagents you require / f i ",I I __, 4—,. -- .' ll ~ “ I I [Gnu/1"). waif "‘f ‘3" " t“ ‘ TC, ll r" I‘ ‘- . _\ r‘ l b ( La; (Jag {I U) i' t2 " x l ' ‘r” 4% .—, I‘: up i, I; " I ., , c/ LI {Jr \ l) a. — t . I: L/ ..- A. 10 7. (15 points) Compound ‘A‘, possessing the Spectral data shown, decolourized a drop of bromine when added. This molecule was found react with borane (followed by oxidative work up) to provide ‘B’, which gave rise to the proton NMR spectra given. Note that when a drop of deuterium oxide was added to the NMR tube containing “13’, and the spectrum reacquired, the signal at 4.51 PPM went away. Ozonolysis of ‘A’ yielded ‘C’ and ‘D‘ that gave rise to the infrared and proton—decoupled carbon NMR data shown, respectively. Interestingly, the spectrum of ‘D' had Only one signal. Treatment of ‘A’ with bromine in water prOvided ‘E’ that displayed two weak signals (MW = 276 and 278) in the parent ion region of the mass spectrum — both of equal intensity. However, the same spectrum also displayed prominent peaks at a molecular weight of 258 and 260. Treatment of ‘E’ with base produced ‘F' that displayed a strong parent ion with a molecular mass of 196, this time as a single peak. Interestingly, when ‘A‘ was treated with meta chloroperbenzoic acid the same compound, i.e., ‘F’ was also formed. When ‘F’ was stirred with sodium methoxide in ether, compound ‘G’ was produced that had quite an active proton—coupled carbon NMR spectrum. Draw the structures of A through G in the boxes provided. \‘sl'nite any useful information outside of each box for possible part marks. .__./ - I - 1H NMR: 7.58 (d, 2H), 7.43 (m, 5H), 7.11 (d, 2H), 4.51 (br s, 1H), 3.35 (t, 2H), 2.52 (t, 2H) ppm - After adding a drop of D20, the signal at 4.51 vanished .. l i- l. :LlJ'vi‘ I"| Ni, k 2 r" - MS: Weak Parent ions: 276 and 278 (ratio = 1 : 1) - Strong fragment ion: 258 and 260 (ratio = 1 : 1) IE! \_ ', g)- _I.’.', u 1,-- .’I( _|-,-.. F' _ f k/ Ft major stretches: 3065,3011,1655,1506cm'1 -. - I. -‘H NMR: 7.52 (d, 2H), - 7.39 (m, 5H), 7.05 (d, 2H), 6.20 (dd, J =15,1o Hz, 1H), 6.08 (dd, J = 15, 2 Hz,1H). 5.99 (dd, J = 10, 2 Hz, 1H) ( . J, mCPBA )4 I _,P JI/Il IF! - MS: Parent Ion: 196 ll ~— ‘(j‘g' Jltuf . i '\ './1_i:/’-.f_.'_a,.njvr,. _..__j“‘ _. “ L} 4144/ ‘I .13; I§-._;,r’;'/UI _.{:I,'lriji . ( Aer/WI !.:=- J 7" IR m‘ajorlstektcflei ”- ‘30 NMR (3072, 810, 2710 (proton coupled): ppm 1604 cm' 201 (t) ppm 1. O3 2. CHSSCH3 _ . i 1 .2’” 71/: "'-. 1 I01 When a drop of Br2 was added to Compound 'A'. the colour dissipated ~- 33/: I; 1" A Vowel/lit" I,” ,.’:L IGI - 13C NMR (proton coupled): 149 (d), 147 (d), 146 (d). 141 (S), 138 (S), 136 (d), 131 (d), 129 (s),80 (d), 72 (U. 62 (Cl) Ppm 'IDI ...
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Exam_Three_1_Answers - WEDNESDAY NAME 1 1:30 —:20 PM LAST...

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