Chemistry 216 First Exam (March 16, 2010) (1 hr 15 min, 80 points) Dr. Kyoung Moo Koh Lab section GSI name Name Please print Signature Student ID# I 8 II 10 III 6 IV 12 V 12 VI 10 VII 14 VIII 8 Total 80 GSI initial
216 W10-Exam #1 Page 2 of 13. Lab section Name I. (8 points) 1) Given below are infrared (IR) spectra of four compounds. The structures of compounds are given below. Assign each spectrum to its compound by putting the letter corresponding to the compound in the answer box above the spectrum. (4 points) A B C D 1 Answer wave number %transmittance 2 Answer
216 W10-Exam #1 Page 3 of 13. Lab section Name 3 Answer 4 Answer 2) Arrange the following four compounds (A, B, C, D) in order of their Rf values when analyzed by thin layer chromatography (TLC) on silica gel-coated plates using CH 2 Cl 2 as the developing solvent. No partial credit is given to this question. (4points) Answer: lowest Rf < < < highest Rf
216 W10-Exam #1 Page 4 of 13. Lab section Name II. (10 points) 1) Protection and deprotection steps are essential for some organic synthetic processes. For the following reaction, carboxylic acids are protected prior to the modification of the amino group and then deprotected under basic conditions. Provide in the boxes below the structure of the appropriate reagent or intermediate compounds. (6 points) 2) If we used 1g of the starting amino-dibenzoic acid (1) and obtain 0.8 g of the final N-acetylated dibenzoic acid (3), what is the theoretical yield and the percentage yield of the final product? Show you work. (4points)
216 W10-Exam #1 Page 5 of 13. Lab section Name III. (6 points) Cholic acid is one of the major bile acids produced by the liver where it is synthesized from cholesterol. This cholic acid can be fully oxidized by oxidants such as PCC, NaOCl, Jones reagents (chromic acids) and Swern reagents (i) oxalyl chloride, DMSO ; ii) N(CH 2 CH 3 ) 3 ). The oxidized product can react with 2,4-dinitrophenylhydrazine (2,4-DNP) to make a DNP derivative. The following scheme shows the process of oxidation and the synthesis of the DNP derivative. Draw the structure of the product for each step.
216 W10-Exam #1 Page 6 of 13. Lab section Name IV. (12 points) Shown below is the procedure used for Experiment 3 (The esterification reaction) 1) Place 0.360 g of p-aminobenzoic acid and 3.60 ml of ethanol in a 10-mL conical flask. With stirring, add 0.30 ml of concentrated sulfuric acid dropwise. In this step you can observe the formation of precipitate. Draw i) the structures of two possible forms of p-aminobenzoic acid and ii) the structure of the precipitate. (4 points) 2) The precipitate will dissolve during the following reflux period, but if it will not dissolve in solution, what should we do? Explain why. (2 points) 3) Write the name of each part or chemicals of the reflux set-up below and show the flow the cooling water by indicating in and out. (6 points)
216 W10-Exam #1 Page 7 of 13. Lab section Name V. (12 points) In experiment 3, you used an alcohol compound as a starting material and oxidized it to make a ketone. The following scheme illustrates the purification process of the product. 1) Fill answer boxes in the scheme, using the keywords in the box below the scheme (3 points) 2) Explain why we need the brine washing process in the purification above. (3points) 3) After purification, you characterized your ketone product using TLC with a hexane and ethyl acetate mixture as the eluent and you got the following result. If you want to increase the resolution of the TLC spots, which solvent should be added to your eluent for running the TLC. Predict the result. (6 points)
216 W10-Exam #1 Page 8 of 13. Lab section Name VI. (10 points) Shown below is the procedure used for Experiment 5 (The reduction reaction) 1) Draw the products for the reduction of benzoin. (3points) 2) The following scheme illustrates the experimental procedure of the reduction of benzoin. Fill answer boxes in the scheme using keywords under the scheme (4 points). 3) Explain why we need steps 3 and 4 shown in the procedure above. (3 points)
216 W10-Exam #1 Page 9 of 13. Lab section Name VII. (14 points) For each of the following synthetic reactions, draw the structure of an organic compound in each of the boxes provided. (8 points) Match each of the following products to its expected IR frequency for the C=O bond stretching adsorption. 6 points) IR absorptions (vc=o): A. 1651 cm -1, B. 1667 cm -1, C. 1720 cm -1
216 W10-Exam #1 Page 10 of 13. Lab section Name VIII. (8 points) For the aldol condensation, 1.5 g of benzaldehyde, 1.14 g of acetophenone, and 7.5 ml of 50 wt % NaOH (d=1.515 g/ml, MW of NaOH = 40 g/mol) were used. 1) What is the molar ratio between acetophenone and NaOH?.(4 points) 2) If you obtained 1.5 g of the product, what is the % yield? (4 points)
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