Chemistry 216 First Examination ovember 6, 2007 ame Key Please Print Dr. Andrew Karatjas (2 hrs, 100 points) Signature Please CECK FF your lab section. section # GSI 130 Thomas Sundberg 131 Peter Mai 132 Peter Ung 133 Therese Dorau 134 Candice Paulsen 135 Ahleah Rohr 136 Justin Lomont 150 Kapil Karki 151 Ben Thompson 152 Thomas Sundberg 153 Candice Paulsen 154 Peter Ung 155 Joseph Jankolovits 156 Ahleah Rohr Student ID # section # GSI 170 Kapil Karki 171 Ben Thompson 172 Peter Mai 173 Therese Dorau 174 Joseph Jankolovits 175 Christopher Taylor 176 Christopher Taylor I 6 II 3 III 7 IV 12 V 8 VI 12 VII 16 This exam has 14 pages including this cover page. The last 3 pages include a periodic table, tables of characteristic IR absorption frequencies of common chemical bonds, and pk a values for representative acids. VIII 9 IX 12 X 15 Total 100
I. ne of the more common uses of TLC is monitoring the progress of a reaction. Using the TLC plate diagrams below, draw in the spots on the plate (after development) for the following reaction. Plate # 1: At the start of the reaction. Plate # 2: At 50% completion. Plate #3: When the reaction is finished. Each plate should have a lane for SM, a co-spot, and the reaction mixture (6 points). LiAl 4 ; acidic workup C 3 Starting Material co-spot Reaction Mixture Starting Material co-spot Reaction Mixture Starting Material co-spot Reaction Mixture Atstartofreaction At50%completion At100%completion II. Rank the following compounds on the basis of increasing R f (3 points). C 2 A B C D Smallest R f < < < A C D B Largest R f
III. Draw a proper setup for a refluxing reaction. Label all of the equipment needed for this setup. Why would you setup a reaction in this way? (7 points) In order to allow the reaction solvent to boil but still retain the volume of solvent you started with. water out condenser water in flask heating bath stirbar IV. In experiment 1, we did the acylation of aniline derivatives. The same type of reaction can be done with phenols. When done with salicylic acid, the product is acetylsalicylic acid or aspirin. The reaction is shown below. Answer the following questions about this reaction. Show all work. (12 points) 2 S 4 MW = 138 MW = 102 density = 1.08 g/ml 9M MW = 180 (a) If you start with 1.5 g of salicylic acid, 2 ml of sulfuric acid, and 2 ml of acetic anhydride, what is the limiting reagent? Salicylic acid: 1.50 g / 138 g/mol = 10.9 mmol ---- LIMITIG REAGET Acetic anhydride: 2 ml * 1.08 g/ml = 2.16 g / 102 g/mol = 21.1 mmol Sulfuric acid: 2 ml * 9 mmol/ml = 18 mmol (b) What is the theoretical yield of this reaction? 10.9 mmol * 180 g mmol = 1.96 g
(c) From this reaction, 1.70 g of aspirin were recovered. What is the actual yield? Yield = 100 * (1.70 g / 1.96 g) = 87% V. For the following sets of compounds, circle the one that is the stronger base (8 points). (a) Me (b) 2 2 2 2 2 (c) - - (d) - - 2 Br VI. The goal of recrystallization is to obtain purified material with a maximized recovery. For the following items, explain why this goal would be adversely affected (12 points). (a) In the solution step, an unnecessarily large volume of solvent is used. Upon cooling, there will still be too much solvent and more (all) of the product will still be in solution. (b) The crystals recovered are washed with additional hot solvent. The hot solvent will redissolve some of the crystals. (c) The solution is allowed to cool before the gravity filtration to remove insoluble impurities. Some of the products will have come out of solution and will also get filtered during the gravity filtation. (d) Crystallization is accelerated by immediately placing the flask of hot solution into an ice-water bath. May get poor crystallization due to the speed some impurities may crash out as well. or The flask may break from the extreme temperature difference.
VII. Fill in the box with the expected outcome of the reaction, or the correct starting materials (16 points). (a) + a (b) 2 S 4 (c) acl o reaction - tertiary alcohol. The hypochlorite would also be an acceptable answer here. Cl (d) + 2 2 2 2 2
VIII. In experiment 1, we made acetylated derivatives of various anilines to make the corresponding acetamides. In a similar fashion, one can make the benzamide derivatives using benzoyl chloride. Draw the full mechanism of the conversion of aniline to its benzamide derivative in the box below (9 points). Cl 2 benzoyl chloride B: + Cl Ph - +
IX. For the following pairs of compounds, explain briefly how you could use IR spectroscopy to distinguish them (12 points). (a) The presence of the methoxy group gives the carbonyl on the right additional single bond character and will shift it to lower wavenumbers. (b) Si The silicon is less electronegative than oxygen and therefore will donate more electron density toward the carbonyl. This will increase its single bond character and push it to lower wavenumbers. (c) igher ring strain higher wavenumbers cyclopropanone will be at higher wavenumbers than cyclobutanone.
X. For the following 5 IR spectra, there are 12 possible structures, assign the appropriate structure to its spectrum (15 points). (a) G (b) A
(c) (d) J
(e) E
A Cl G B 2 C I D C J E K F L