ORGANIC CHEMISTRY I (2301) 9:30 10:45 am, August 2, Final Exam

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1 NAME ID # RGANIC CEMISTRY I (2301) 9:30 10:45 am, August 2, 2012 Final Exam There will be two ways that you can pick up your graded Final Exam: You can pick up your graded exam from Andy at office hours that he will hold on Monday, August 6 th (9:30-10:30 am) at Coffman Union Starbucks. Alternately, you will be able to pick up your graded exam from Chemistry department staff in 115 Smith beginning Monday, August 6 th at noon. Exams that are not picked up within two weeks will be disposed of. A periodic table, a chart of reaction conditions, and a table of typical NMR chemical shifts are attached to the back of this exam as aids. therwise, you are not permitted to use any other materials (including notes, books, or electronic devices of any kind). Right now, write your name and student ID number at the top of this page. When the exam begins, please write your name at the top of the next page. You may use pen or pencil. owever, re-grades will be considered only for exams completed in pen. Please write your answers in the boxes/spaces provided. If your answer is not in the appropriate space (say, for example, it s on the back of the page), draw us an arrow and/or note telling us where to look. 1

2 NAME Scoring: 1. / / / / / / / / / 8 Total Score: / (14 pts) For each of the pairs of acids (or bases) below, Draw the conjugate base (or acid). Circle whether you think the first acid (or base) is more or less acidic (or basic) than the second. Acid Conjugate Base Base Conjugate Acid N 3 C C 3 is is MRE ACIDIC LESS ACIDIC MRE BASIC LESS BASIC than than 3 C C 3 2

3 2. (15 pts) For the anion drawn at right, in the boxes provided: Draw all significant resonance structures. In each structure, draw all atoms, bonds, lone pairs of electrons, and formal charges. Then, circle which resonance structure you think is the most significant, and which is the C C C C least. Circle only one MST and one atom hybridizations: LEAST. Draw a Lewis wedge/dashed-bond structure that illustrates the most stable threedimensional conformation of the molecule. Draw all atoms, bonds, and charges, but omit lone pairs. C C C N C In the boxes provided, write the hybridization state on any atom heavier than MST or LEAST significant? hydrogen. 3-dimensional representation resonance structure MST or LEAST significant? 3. (12 pts) Each of the reactions below and on the next page is drawn with two possible products. If one of the two products predominates, circle that preferred product. If the two products are produced equally, circle BT. If neither product would result from the reaction, circle NEITER. Circle one answer only. C 3 Et C 3 C 3 C 3 C 3 C 3 BT (equally) NEITER 3

4 3 C C 3 mcpba C 3 3 C 3 C C 3 BT (equally) NEITER 3 C C C C 3 2 (1 equiv) 3 C C 3 3 C C 3 BT (equally) NEITER 4. (15 pts) For each of the reactions below, fill in the empty box corresponding to the major product. Wherever appropriate, illustrate stereochemistry in your drawings (using wedge and dashed bonds). If multiple enantiomers or diastereomers are produced, indicate this in the answer box (e.g., by writing + enantiomer, etc.) N (NBS) AIBN C 3 2 S 4 2 4

5 C 3 Na 5. (8 pts) Each of the reactions below is drawn with two possible reaction conditions. If only one of the two reaction conditions would generate the given molecule as the major product, circle those conditions. If both sets of conditions would accomplish the reaction, circle BT. If neither set of reaction conditions would succeed, circle NEITER. Circle one answer only. Na 2 Cr S 4 1. (CCl) 2, DMS -60 C 2. Et 3 N (Swern oxidation) BT would work NEITER would work Na, N 3 Pd, BaS 4 quinoline, 2 (g) (Lindlar s catalyst) BT would work NEITER would work 5

6 6. (25 pts) When the epoxide-alcohol starting material below is deprotonated with Na, the resulting alkoxide reacts with itself to open the epoxide. That reaction, followed by acidic workup, can produce two different products; the difference between the products is dictated by which epoxide carbon is attacked by the alkoxide. C 3 1. Na (- 2 ) C 3 Na intermediate A intermediate B product A product B In this problem, we will name the products A and B, which are formed by protonation of intermediates A and B. (a) Using electron pushing, draw a mechanism that illustrates the formation of intermediates A and B from the alkoxide. I ve drawn the starting material for you just add curved arrows to my structure. Then, draw the structures of intermediate A and intermediate B. Wherever appropriate, illustrate stereochemistry. C 3 push electrons here C 3 intermediate A intermediate B the (b) Is intermediate A MRE LESS SAME intermediate B? STABLE STABLE ENERGY (Circle one.) than than as 6

7 (c) n the potential energy diagram below, draw two curves that represent the two reactions you drew in part (a). The starting material (alkoxide) energy has already been drawn for you you need to connect this starting point to energies of the reaction transition states, intermediate A, and intermediate B. C 3 E starting alkoxide reaction coordinate intermediates A/B (d) ow would the rate of the two reactions be affected if the starting material were a thiol instead of an alcohol? Assume that the thiolate on the right has the same energy as the alkoxide above, and that the sulfur-containing intermediates A S and B S are also the same energy as intermediates A and B. Would the thiolate react FASTER than SLWER than the SAME RATE as C 3 the alkoxide? (Circle one.) S 7

8 7. (16 pts) Draw a mechanism (using electron pushing ) for each of the reactions shown on the next page. Draw each mechanistic step explicitly; don t cheat by combining multiple processes in a single step. Use only the molecules shown in the problem; don t invoke generic species. (E.g., don t use -A as a generic acid.) 2 S 4 Mechanism: 8

9 8. (16 pts) For each set of starting materials and products shown below, propose a multistep synthesis. In addition to the molecules shown, you can use any reagents and reactions we ve learned about in class. You might discover multiple answers to this problem; draw only your best (one) synthetic route. Feel free to draw an incomplete route we will give you partial credit where we can. C C 3 C Multistep synthesis: 9

10 9. (29 pts) Acrylonitrile, the starting material on the right, can be polymerized into polyacrylonitrile (a component of plastic consumer goods) by heating it in solvent, but heating acrylonitrile in a mixture of ethanol and water generates a small molecule product instead. This product was isolated and characterized by NMR and IR spectroscopy and mass spectrometry; the spectra of this product are shown on the next two pages. igh-resolution mass spectrometry determined an exact mass of amu for the highest-mass (parent, M + ) peak in the MS spectrum, which corresponds to a molecular formula of C 5 9 N. (a) Based on the features in the IR spectrum below, what functional groups would you expect the unknown molecule to have? Circle all answers that apply. CN 2 C 3 C 2 C 5 9 N C (sp) C(sp 2 ) C(sp 3 ) N C N C C C C C C N IR Spectrum: 100 Transmittance (%) (wavenumbers, cm -1 ) (b) What is the structure of the product? In the box on the next page, draw the molecule s structure, including all hydrogens. Then, considering the 1 NMR spectrum, 10

11 Circle each group of equivalent s; Assign a 1 chemical shift ( ) to each circled group, within 0.05 ppm; Connect any pair of coupled, inequivalent groups of s with a double-headed arrow, and then label that arrow with the corresponding the product (C coupling constant (J). 5 9 N) Format for answer to (c): J = 7.0 z Cl = 2.2 ppm Cl = 3.8 ppm 1 NMR Spectrum: 11

12 (c) In an electron-ionization (EI) mass spectrometry experiment, parent ions often fragment into daughter ions that give information about the parent s molecular structure. In the EI mass spectrum below, the parent mass peak at m/z = 99 corresponds to a radical cation (M + ) that fragments into ions with mass 84 and 59. In the boxes below, draw the structures of these ions. You do not need to do electron pushing to answer this question just draw the cations. n all ion structures, make sure to specifically illustrate where the formal charge lies. M + (C 5 9 N +, m/z = 99) fragment ion with m/z = 84 fragment ion with m/z = 59 Mass Spectrum: Relative Intensity m/z 12

13 Final Exam Chart of Reaction Conditions Pt/ 2 (g) 1. B 3 TF , - 2 S 4 2 mcpba 2 Cl 2 or 2, h NaN 2 Pd, BaS 4 2 (g) N (quinoline) Na 2 Cr S (C 3 ) 2 S Na N 3 1. (CCl) 2 DMS -60 C 2. Et 3 N (Swern oxidation) Cl KMn 4 (cold, dilute) 2, - SCl 2 pyridine (mcpba) TsCl pyridine N (NBS) h or AIBN gs 4 2 S 4 1. KMn 4 KMn 4 K, , p 7 P 3

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16 Gold Periodic Table of the Elements Chemistry Reference Sheet California Standards Test A 1 ydrogen Li Lithium 6.94 Na 11 Sodium K Potassium Rb Rubidium A 104 Rf Rutherfordium (261) 42 Mo Molybdenum Atomic number Na Element symbol Sodium Element name Average atomic mass* Cs 55 Cesium Fr Francium (223) Be 4 Beryllium 9.01 Mg 12 Magnesium Ca Calcium Sr Strontium Ba 56 Barium Ra Radium (226) 3 3B 21 Sc Scandium Y Yttrium La 57 Lanthanum Ac Actinium (227) 4 4B 22 Ti Titanium Zr Zirconium f afnium B 23 V Vanadium Nb Niobium Ta 73 Tantalum Db Dubnium (262) 6 6B 24 Cr Chromium B 43 Tc Technetium (98) W 74 Re 75 Rhenium Tungsten Sg Seaborgium (266) 25 Mn Manganese Bh Bohrium (264) Key 8 26 Fe Iron Ru Ruthenium s 76 smium s assium (269) 9 8B 27 Co Cobalt Rh Rhodium Ir Iridium Mt Meitnerium (268) Ni Nickel Pd Palladium Pt Platinum B 29 Cu Copper Ag Silver Au B 30 Zn Zinc Cd Cadmium g 80 Mercury A Boron A B 5 Carbon Al Aluminum Ga Gallium In Indium Tl Thallium Ge Germanium A C 6 Nitrogen Si Silicon Sn Tin Pb 82 Lead A N 7 xygen P Phosphorus As Arsenic Sb Antimony Bi Bismuth A 8 Fluorine S Sulfur Se Selenium Te Tellurium Po 84 Polonium (209) 18 8A e 2 elium F 9 Ne Neon Cl Chlorine omine I Iodine At Astatine (210) 18 Ar Argon Kr Krypton Xe Xenon Rn 86 Radon (222) * If this number is in parentheses, then it refers to the atomic mass of the most stable isotope. Ce 58 Cerium Th 90 Thorium Pr Praseodymium Pa 91 Protactinium Nd 60 Neodymium U Uranium Pm 61 Promethium (145) Np 93 Neptunium (237) Sm 62 Samarium Pu 94 Plutonium (244) Eu 63 Europium Am 95 Americium (243) Gd 64 Gadolinium Cm 96 Curium (247) Tb 65 Terbium Bk 97 Berkelium (247) Dy 66 Dysprosium Cf Californium (251) o 67 olmium Es 99 Einsteinium (252) 68 Er Erbium Fm 100 Fermium (257) Tm 69 Thulium Md Mendelevium (258) Yb 70 Ytterbium No Nobelium (259) Lu 71 Lutetium Lr Lawrencium (262) Copyright 2008 California Department of Education