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Unformatted text preview: Page 1 of 11. (+ 2 blank pages + periodic table) C263 Sections B1/B3 ORGANIC CHEMISTRY Midterm Examination (100 Points) February 28, 2008 Name: 8 I M E; KE 2 (Please Print) ID#: Signature: 1. (06) 2. (08) 3(a, b). (10) (c—e). (12) (fig). (11) (H) (12) 4(a,b). (08) (c—D- (15) __ (g—i). (10) 5. (08) TOTAL (100) Do not open this examination until you are told to do so. 0 Make certain you have all the pages of the exam (10, including this one). Write your name on each! a If you use the blank pages (or any backsides) for any answers, make certain you write a note directing the marker to the appropriate location. - You may use molecular models and an otherwise unmarked template/stencil, but no other papers, etc. You may not share molecular models (and please use them as quietly as possible!). 0 It is your responsibility to avoid any situation that could be construed as academic misconduct. Re-marking Procedures Errors are occasionally made in grading the tests. To request re-marking of your examination, you must explicitly follow this procedure: (1) Consult the answer key for the correct answers and some idea of how the points were assigned. (2) All re-grade requests must be submitted by the next lecture period after the tests are handed back. (3) Requests must be in writing, stapled to your exam. The requests should state (a) which question(s) you want re-graded and (b) why you want the question re-graded. (4) DO NOT MAKE ANY MARKS ON YOUR EXAM. If your exam is modified in any way, no re- marking will be considered. Examinations done in pencil cannot be re-marked. ,/ Name — 2 1. Provide structures for the reasonable contributing resonance structures for N-methylpyridone, shown below. Use your judgement for what constitutes reasonable, but drawing only the most contributing ones will be sufficient for full credit! Also for full credit, comment on any structures that look particularly important to the weighted average that represents what this compound really looks like. Hint: In addition to the original drawing, I can come up with seven contributing structures, some of which are not very contributing (and thus not essential to gaining credit!). (6 points) Meéj >9" ocfiee‘l’ MKOVA') MotX‘ed :fi- 3Q MS Lip 5 gar Sin/mimic, \mhw/ Sets 1;“ 04\g\-Q + 1M\Q g-‘Nggl-VJQS “A: CMA'QJVA" abort QML\)€\{ \s maid ilk even v? «bi QMK. 6-ngng Q16 no"\' Vac/Jr of E Elam; ‘ mm «mm «AM Samara mam. Name—3 2. One electro hilic aromiatc substituion reaction that we have not specificall discussed in class is called . . p . . . . y . “aryldlazonium coupling” and it IS often used to create organlc dyes as colourants. One example of thls process is shown below. Consider this reaction and address the following issues. 0M9 + N N? N + —b- (8 points) | N + HCI / 0 H035 (a) Diazonium salts are reasonble electrophiles, reacting with activated arene systems at the terminal nitrogen, as shown. Show how it is possible that the reaction occurs on the terminal nitrogen of the diazo functionality even though it is the internal nitrogen that is cationic. In a few words, explain. lifts x, e 295%er Sim-A 416% ®.// é” Axe, JCW‘flQQ N °\\So No .... .- H%§©/ c“) I / Sim-LS ‘WL posi‘lwe W H . § AW 5 mSOoiwo—‘ted (“K vmmoa alarms) . (b) Provide a step«by-step mechanism for this reaction, including arrow pushing rationalization and all relevant intermediates. Be sure to explicitly account for the position of this substitution reaction. Ole "amt 6» “L flj’ a\ ____i, “fl, ML 5 (a N 5 LlS- gN-sug? "ha-gel ‘ / H§ 0‘63 ”8*? Paid/U0“ . Vqrflm‘ts aka-1 IQ CG” “6““1 rfsqm 2 ctLWMA 93. Natures (c) Very briefly, explain why the reaction product is intensely colored. Ht Lt COM ‘CQA '11-'5st @RCAQ "l Ffi'S «a 0mg mo m visible “3137 WSW/‘9? at wit/wag. seam! Name 4 3. Short answer. Provide the requested information. Please do not be unnecessarily long-winded! (3) Consider the heterocyclic compound 1—methylboracyclopentadiene, shown at the Z/ \3 right, and address the following queries and issues. B (7 points) | 323* «lo -- (a) In the space below, draw an enery diagram showing the relative energies of these orbitals (do not USO. F1) try to draw depictions of the actual orbitals themselves!) Label the “zero energy” (nonbonding) FfOS’l' ‘3 level on the axis and label each orbital as bonding, nonbonding, or antibonding, as appropriate. CA “'sz (lfflb) Show clearly which orbitals are occupied and which are unoccupied (i.e., virtuall). p \cj‘ lp-l- (1‘ prc) Identify this compound as aromatic, anti-aromatic, or nonaromatic. “Nit QM+ 0 P1) ((1) Draw a depiction of the lowest energy (most stabilized) Jt-molecular orbital for this compound. Use the space to the right. A pg: MM 3 d. , \S glfiQz - . mi.“ (312/3? 3 C 'h ‘2‘": . . . . . . . (b) Comp e the ba3101ty of N,N-dimethylamlme and benzyldimethylamme, shown below. Identlfy which of the pair is more basic and briefly explain your rationale. (3 points) Me . TL“? Iowa. pour IS QM N‘Me vs. I I [SING M \OCQ ‘10:; 0v\)c\\.Q NT" . p O Me bQS‘C ‘30 H B °~\\ ‘V‘Lexfi Owoul' IO? $ 0M2 far macaxon blood. \ , ’2. .5 I a mthng \mm‘r \s \ovsxl W3 €$.p\flwf\'h~ M pagovowaa dpvachcx—x ionA ($2?th Sidelines 4L: \-\>.qu SWFS E—lovt CNQX mvH'x‘pQ W M» ‘91 WW9 W ’“4\ PM gait/L simumffi. S Name —_+___ 5 (c) The orthowquinodimethane shown below (good thing we didn’t have do much nomenclature this term!) is among the very best dienes for the Diels—Alder cycloaddition, reacting with common dienophiles rapidly even at room temperature. Consider both the structure of this diene and it’s use in a Diels—Alder reaction: provide a rationale for this unusually high reactivity. (4 points) Hint: there are TWO principal reasons for this! C: “/5 (1) 1'an (heme 1S nice/i6 S-“CAS (0mg- commit + 2‘75 Mega QM»! QrOM lavwg 9—015 i This '5 gma (2-) Inata D-A mac/Jew 4M; «heme QMWJC B'iCdMES RROMHTIQ +lfi§ pmv‘&\‘:§gq Sjrwwg W Ice lief F701 - d f \ V] (d) Consider the following energy diagram for kpothetical reaction that gives two products. Identify (circling usually works) and label (with the corresponding letter at least) on the diagram the locations andfor quantity requested in the items listed below: m \ (2+ eat-L «ad—A ‘4 pm” (A) ,__ (a) A thermodynamically unstable intermediate 1 a QC, “A... ’ " A5 (b) The kinetic product obtained in the reaction 3 (c) The energy difi'erence (AG0) between kinetic and WFIU G" ""'—"' thermodynamic products —- (d) The activatlon energy for the rate determining step of C0) the reaction reaction coordinate (e) For each compound shown below, designate whether it is (i) aromatic, (ii) anti-aromatic, or (iii) non-aromatic. Consider each structure in it optimal conformation and write your _ answer on the blank line under each structure. (4 pomts) \ pi", act elm Q Q 0 "NH “-l’ll c9 Omi". art-Nu , armwriic han— arm (Aroma): 1': "Cad M10 11 Name (f) Consider each statement carefully and circle whether it is true (T) or false (F). (7 points) \ Fl ecu/h l (i) The electronegativity of carbon is strongly influenced by hybridization. @ F (ii) Diels-Alder reactions enerall rovide the thermod amically most favorable g y P Y product under normal reaction conditions. T (iii) The allyl cation is best re resented by two carbocationic structures in ra id P ___E_. m /\/7 e uilibrium, each bearing an alkene and a cationic primary carbon. T (iv) The number of nodes present in a molecular orbital (MO) correlates roughly with its relative energy. F (v) Resonance effects generally dominate over opposing inductive effects. T F (vi) UV/visible spectroscopy involves promoting an electron from the HOMO to the LUMO of a compound. F (vii) The HOMO/LUMO energy gap in an organic compound decreases as a function of increasing conjugation length. F (g) Assign as many of the resonances in the 13C NMR spectrum of 5—hexen—2-one as logic allows. Place your assignments (by letter) in the blanks provided, but note that it is almost certainly not possible to fully assign each signal unambiguously! For those ambiguous cases, just indicate that an assignemnt cannot be made with confidence. (4 points) Name _ 7 - - - ound Cfile, which by infrared spectrscopy shows weak absorptions at both 15050 cm“ and cm . Deduce the structure of this simple hydrocarbon and . . "‘ hile no detailed explanation is required for full credit, partial credit credit will be given for inCOrrect answers accompanied by correlationsfassignments. mm ;' .9- (4 points) W 4 IHMW 3W Marika?- ffifll‘gf Sigwmefijtwfi ({Fipld ‘go 5 gwé \ £01 W - 5.42.5 . . (I? saw?— rm new 3:0 2. S vgleris TU assgvx— 1% l *‘V'Pie’f (“A/8M ‘10 2M} “may “(5 “KN/UL , (i) For each of the following compounds, deduce the number of resonances you expect to see in the 1H NMR spectrum of each compound. Place your answer on the line beneath each structure. No explanations are necessary, but feel free to offer any com nts you deem relevant! N, C/fl (4 points) CI \TA/CI \rj\ >(\ be M‘- W in; ' r'efiya‘tie-la J- —5; fl ._ 3 ”A [Vt-W81 5W3 (j) Rank the following four compounds in terms of decreasing rate toward electrophilic aromatic substitution reactions (1 2 most reactive, etc.). (4 points) 0 Br 0 . / ....\ IQM O O \(r)K m GAO " M _3_ ,|_ A il— .l.‘ Ear {vidwraMa—Xwa laxi- hung «the. (ALP/’3 rflzlawkwvdq (PI W1C)? Name 4. Predict the products of the following reactions or provide the reagents and reaction conditions necessary to effect the given transformations. If more than one product is anticipated (stereochemistryl?) and there is reason to expect a selective reaction, indicate clearly which will be major. Use the available space outside the box for drawing intermediates (partial credit, ehl), but mechanisms are not required and your answer must appear in the box. Where reagents are requested, more than one step may be required. Where stoichiometry is not explicity stated, assume one equivalent of the reagent. (33 points total) 50 °C, 12h H + HBr g) \ (1 equiv) OH OH OH BHT, an anti-oxidant (preservative) lgk- k "SU Wax-wk 5.3.1! (“V‘sy 05" 4M. wag Name g_ b/ HN03 2 H2804 «)6 . \4 Me. $83st We (5‘3”ka «give—ARA Ling 0%» N's) 26 WW— Wm M; ML) aéc'wrhé ei (Two compounds) 2 equivs Br2 i' FeBr3 (xs) 0 . Br.» W6 w l O ‘—-’ /’ fit 90: vamé 3+ MS 10 V1147" ~417me .1 bit" PVHVj H w 0 ET 0‘] O ”W P 93% Name____fi_11 5. Deduce the structure of the compound with molecular formula CQHIDOZ, using the IR and 1H NMR spectra provided below. For full credit, provide the details of your deductive logic, showing substructure analysis and specific assignments for all relevant signals observed in both spectra. Providing the correct structure alone is worth a relatively minor amount of credit. (8 points) '-'9\.Wr=.;, _ ,1 "- ax‘flm'gg’é‘afil‘ ., u: 5“; '55 5 5 .3 E. El 3 3 E E : “, unSQ-kpcul’ IONS )IR l 50%;} aim-Mlle. looks. ...
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