Chemistry 216 First Examination March 11 th, 2008

Transcription

1 Chemistry 216 First Examination March 11 th, 2008 Dr. Andrew Karatjas (2 hours, 120 points) Name KEY Signature Student ID# Please check your lab section Section # GSI Name Cherie Netzloff Vitaly Volberg Amanda Ward Aireen Romu Asako Kubota Jin Zhang Christopher Taylor Aireal aley Travis Clark Sarah Simmons Devon Riter Diana Dinh Michael Asuncion Yuta Suzuki Daniel Dawson Eric Majchrzak Thomas Slaney Amberlyn Wands Peng Song Megan Beems Therese Dorau Joseph Jankolovits Kaysia Ludford Brianne Dzwonek Aireal aley Amberlyn Wands Sarah Simmons Christopher Taylor Devayani Bhave Jenni Westerhuis Daniel Dawson Amanda Ward Jing Chen Devon Riter Diana Dinh Michael Asuncion Yuta Suzuki Eric Majchrzak Thomas Slaney Jacob Begres Section # I 9 II 7 III 10 IV 15 V 9 VI 13 VII 20 VIII 13 IX 9 X 15 Total 120 GSI Name Aireen Romu Jinhui Chen Lindsay Saunders Vitaly Volberg Travis Clark Jing Chen Peng Song Ian McLachlan Therese Dorau Jessica Lee Jin Zhang Kaysia Ludford Jinhui Chen Brianne Dzwonek Shaun Patel Kristy Bojazi Devayani Bhave Asako Kubota

2 I. ne of the more common uses of TLC is monitoring the progress of a reaction. For the reaction drawn below, draw in the spots (after development) on the TLC plate diagrams drawn below. 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 starting material, the reaction mixture, and a co-spot. Show only the spots for starting material and product (9 points). Ac 2, NaAc Starting Material co-spot Reaction Mixture Starting Material co-spot Reaction Mixture Starting Material co-spot Reaction Mixture At start of reaction At 50% completion At 100% completion II. Rank the following compounds on the basis on increasing R f. No partial credit will be given on this question (7 points). A B C D B< C < D < A Smallest R f Largest R f

3 III. Draw and label all of the parts of the setup for a steam distillation (10 points). IV. For the following esterification reaction, show all work when doing the calculations (15 points). 2 S 4 MW = 122 MW = 108 density = g/ml MW = 212 a. If 2.44 g of benzoic acid, 6.20 ml of benzyl alcohol, and 0.5 ml of sulfuric acid are used, what is the limiting reagent? Sulfuric acid catalytic Benzoic acid 2.44 g/122g/mol = 20 mmol LIMITING REAGENT Benzyl alcohol 6.20 ml * g/ml = 6.48 g/108 g/mol = 60 mmol b. What is the theoretical yield of this reaction? 0.02 mol * 212 g/mol = 4.24 g c. From this reaction, 2.00 g of product was recovered. What is the percent yield of this reaction? = 2.00 g / 4.24 g * 100 = 47%

4 V. In experiment #1, some anilines required up to 6 equivalents of acid in order for them to successfully go into solution. f the following 3 anilines, predict which one would require the largest amount of acid and explain your reasoning (int: When each is protonated, which one would have the lowest pka?) (9 points). Me N 2 N 2 2 N N 2 Due to the electron withdrawing group, the p-nitroaniline would have the lowest pka when protonated. This makes it the toughest to protonate meaning it would need to be at a lower p to be protonated. Recall: B + K a B: + + [B pk a = log ] [B:] + p The lower the pka, the lower the p needs to be. 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 (13 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.

5 VII. Predict the result (or starting material(s)) for the following reactions (20 points). 1. Cl N 2 (a) 2. - Na + N (b) cat + (c) NaB 4 (d) + Na No reaction - no enolizable protons on either compound.

6 (e) NaCl VIII. It is always important for your glassware to be clean and dry when running a reaction. This is especially important in the aldol condensation. Draw the mechanism for what might go wrong if you had acetone left in your flask when trying to do an aldol condensation using benzaldehyde (13 points). + Na IX. The following carbonyl compounds have IR shifts of 1830 cm -1, 1715 cm -1, 1650 cm - 1, and 1730 cm -1. Assign the IR shifts to the correct compounds (9 points). F 1730 cm cm cm cm -1

7 X. For the following 5 IR spectra, there are 12 possible structures, assign the appropriate structure to its spectrum (15 points). K I

8 D G

9 F A G Cl B C N I D N 2 J N E K F L