347practice_exam_spring_2006_final_exam

347practice_exam_spring_2006_final_exam - YOUR NAME:...

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Unformatted text preview: YOUR NAME: Chemistry 347 Final Examination Spring, 2006 Professor Hopkins /6 /5 /8 /14 /14 /14 /8 /8 /10 /13 HomsgwewNH .O - Total: /100 You are responsible for confirming that this examination contains 10 pages, including the cover sheet. 1. (6 points) Draw the chemical structure of each of the following substances you have used in this course. For example, ethyl acetate is: o H3C’8'0“QHLCH3 a. - Nitrous Acid b. Acetic Anhydride c. 2,4-Dinitrophenylhydrazine 2. (5 points) In the glucose acetylation experiment, explain clearly how you were able to use proton NMR spectroscopy to assign the ratio of the 0t- and B-anomers of glucose pentaacetate. 3. (8 points total) a. Sketch below the two-step synthesis scheme you used to prepare a candidate sulfa drug, showing chemical structures of the starting materials, products, and key reagents. Please do not use abbreviations (“Ac”). No mechanisms are required. b. What was the purpose of the acetyl group in the first step? What might have happened if it had not been present? 4. (10 points) a. Sketch below the three-step synthesis scheme you used to prepare a candidate dihydrofolate reductase inhibitor, showing the chemical structures of the starting materials, products, and key reagents that YOU, specifically, used. Please do not use abbreviations (“Z”). No mechanisms are required. b. What was the purpose of the carbobenzyloxy group used in the first step? What might have happened if it had not been present? c. Draw the structures for the starting material and product of the chemical reaction catalyzed by dihydrofolate reductase. It is fine to use partial structures; just be sure to show the key portions of the molecules that are transformed. 5. (14 points total) In each of A-G, you are provided a sample of a single pure substance with one of the two indicated structures. Describe briefly what solubility test, chemical test, or spectroscopic technique you would use to determine the one correct structure to your sample. THE NMR MACHINE IS BROKEN; you cannot use NMR. No table of derivative properties or authentic samples are available to you. If you use a chemical or solubility test, indicate what conclusion a positive or negative test affords. If you use a spectroscopic test, tell what spectroscopic feature(s) you would look for, and how you would interpret it. Q A. l‘ 0H ,CH \ oH H3 Q/ C‘CHL/ ch L 9/ o B /CHLOH “Cf/{\CHLOH \AQF 3 (DH C ‘ O CH / 3 QQHLCHZ Q” oi“ D. CH3 OH / ‘ HO {NHL q \ 3 G (EH2 l _ 1,, 0 OH 6. (14 points total) In this question, you are asked to consider what partial structures are likely present, likely absent, or about which you cannot tell, given some experimental observations. You are NOT asked to draw the complete structure of any molecule! a. An unknown substance shows the following properties: Insoluble in water or dilute aqueous acid, but soluble in aqueous sodium bicarbonate Negative 2,4-DNP test Positive chromic acid test Positive iodoform test i. Draw TWO sub—structures (for example, functional groups) that are VERY LIKELY to be present. ii. Draw TWO substructures that are VERY UNLIKELY to be present. iii. Draw TWO substructures the presence or absence about which you have learned nothing from the above results. b. An unknown substance shows the following properties: Insoluble in water or dilute aqueous sodium hydroxide, but soluble in dilute aqueous acid Negative Tollens test Positive 2,4-DNP test Negative acetyl chloride test No reaction with nitrous acid i. Draw TWO sub—structures (for example, functional groups) that are VERY LIKELY to be present. ii. Draw FOUR substructures that are VERY UNLIKELY to be present. iii. Draw TWO substructures the presence or absence about which you have learned nothing from the above results. 7. (8 points) Assign a structure to substance A, CgH7BrO, insoluble in dilute aqueous acid or strong aqeuous base, negative chromic acid test, positive 2,4-DNP. The infrared spectrum shows a strong broad absorption at 1680 cm"1 (5.95 u), and broad medium intensity bands at 820 and 750 cm"1 (12.2 and 13.4 u). The proton NMR spectrum consists of a doublet (2H) at 8 7.8, a doublet (2H) at 5 7.6, and a singlet (3H) at 5 2.6. 8. (8 points) Assign a structure to substance B, which gives an M+ at m/e 116, and an M++l peak 6.5% +/— 0.5% as large as the M+. Combustion analysis shows the compound is 62.1% C and 10.3% H. No halogens or nitrogen were present. B was insoluble in dilute aqueous acid or strong aqueous base, but soluble in concentrated sulfuric acid. B gave negative chromic acid and 2,4—DNP tests. The IR spectrum of B showed a strong peak at 1740 cm'1 (5.75 u), and no absorbance above 3000 cm'1 (3.33 u). The proton NMR of B consisted of two singlets, in a ratio of 3:1 at 5 1.2 and 3.7, respectively. 9. (10 points) Draw the three structures for C that are most likely, given the data below. C has a molecular ion at 161, an M++1 consistent with six carbons, and M++2 and M++4 (at m/e 163 and 165) consistent with two chlorines. C was insoluble in aqueous strong base, but soluble in dilute aqueous acid. C gave a positive test with acetyl chloride. Exposure of C to nitrous acid, followed by B-naphthol, gave a brilliantly colored precipitate. aa'aussssuaig l l 12 I: I4 15 I6 WAVELENGTH IN MICRONS '30 20 w ;I f! 10' 9 10. (13 points) Draw a structure for D, whose proton NMR spectrum and IR spectrum are shown below. D, C11H17NO, is insoluble in dilute aqueous strong base, but is soluble in dilute aqueous acid. It gives a negative nitrous acid test, negative 2,4-DNP test, but a positive chromic acid test. wAVBdUMIR CM" 4000 3000 2500 2930 15:90 . 1:990 woo 1000 900 500 700 650 625 loo ' ' ‘ ' ' ' ' ' ' too 90 I 90 so axsusznaig'. o 2.5- I J 4 5 5 ‘6 7 8 9 l0 ll 12 13 ll ‘5 16 WAVELENGTH IN MICRONS ggfififii Selected Infrared Absorption Data Out-of—plane bending for sp2C-H bonds: (m1) R“ Q“ 2 CH2, 910, 990 (+overtones 1820) R i /H - “ Q : C \ I 970 H R H \ Q : Q / H 700 / C \ R( 890 k c 2 C H L \2‘ / ‘2 . / H 815 \Q : C / \ n \2‘ fl 5 R 690 (strong, always), 750 (strong, usually) {h o n c) \ I " 750 (strong) (3 r CL0 ‘5' ,— 690, 780 meJC Q \ I R '2' 800-850 (strong) ...
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347practice_exam_spring_2006_final_exam - YOUR NAME:...

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