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Unformatted text preview: Circle one: | wish to have my exam I wish to pick up put in the rack. my exam. Printed Name (Please print clearly) Signature CHEMISTRY 252 Exam | February 8, 2007 100 Points 6:30—8:30 PM This exam has 8 problems on pages 2 through 8. RULES 1. The use of a calculator and model kits are not permitted. 2. This exam is closed book and closed note. No aids other than writing implements are permitted. 3. Answer the questions in the spaces provided on this exam. 4. If you wish to ask a question about procedures or about a problem on the exam, raise your hand. TOTAL: I100 1. Predict the major product or products (be inclusive) that you would expect to be formed in five of the following seven reactions. If you feel that no reaction will occur, then answer no reaction. Be sure to answer only five problems. If you answer more than five, then only your first five wlll be graded. (10 pointsl 2 pts. each) Me 1 equivalent (a) —. Brg OMe 0H Na20r207 ‘” DOC H2804 MeO 1. HN03, H2804 I: 2. Fe (or Sn) HCI Br 0 Br 1 equiv. Eng (d) ‘ —* NH3 N02 Me 1. Me9—CI Me AICI3 (f) G i H‘isi M 2. KMnO4, heat CO, HCI (g) “_—"” CuCI. AlClS FeBr3 (9) Br CH3 9 2. Fill in the reagents needed for accomplishing two of the three following transformations. More than one step is required. Remember that the order of the steps in a synthesis is important. Be sure to answer only two problems. (6 points! 3 pts. each) (a) G/“v OMe Chris 0 (h) K: ——-+ GAGE Br NH2 CH3 CH3 E: 3. 3. Consider the following equilibrium reaction. Use the pKa values given to predict the equilibrium constant (Keq) for the reaction. (5 points) \ Keq = ? \ M . [j Z M + [j ,N\ / N +/ H H h' H [Ti H pKa = 0.4 pKa = 5.2 b. Why does the reaction favor the cation suggested by the pKa’s‘? Please restrict your answer to no more than one sentence (only your first sentence will be graded) and an appropriate orbital picture. (5 points) 4. At a recent scientific meeting I attended one of the attendees argued that the cyclopropenyl radical illustrated below is “non-aromatic”. H a. The individual in question based their argument upon “H'Lickel’s Rule”. A Why did they reach their conclusion that the molecule was non- H H aromatic? Again, restrict your answer to no more than one sentence. (4 points) b. However, in class we did not use Hfickel’s Rule to define aromaticity but rather employed a molecular orbital diagram. With this in mind, draw the molecular orbitals for both the cyclopryopcnyl radical and its acyclic counterpart, the ally] radical. (6 points) c. Draw an energy orbital diagram being sure to populate your orbital levels with the appropriate number of electrons. If you have already clone this in part b, then there is no need to repeat it here. Just write see above in the space below. (5 points) d. Using your orbital energy diagram, is the conclusion that cyclopropenyl radical must be non-aromatic correct? Why or why not? Please restrict your explanation to one sentence. (5 points) 4. Draw a “curved-arrow” mechanism for both of the following reactions. CL CM? 3. (5 points) b. (5 points) Br NH2 1. 803. H2504 2. 'NH2 SOSH 5. a. What is the Hammond postulate? (5 points) I). Use the Hammond postulate to explain why the following reaction goes on‘the central ring of anthracene. Please restrict your answer to no more than one or two sentences and any drawing/drawings that you feel are appropriate or helpful. (5 points) Br 0.0 Br 6. Cycloheptatrienone (compound 1 below) gives rise to an unusually intense carbonyl stretch in an infrared Spectrum. 0 O 1 2 3. Why? Please restrict your answer to no more than one or two sentences and an appropriate drawing. (5 points) I). Would the carbonyl stretch for 1 come at higher or lower wave number than the carbonyl stretch for 2? Why? Please answer using only one sentence. (4 points) 7. A graduate student in my group recently designed a “cleavable—Iinker” for detecting molecules on a surface using mass spectrometry. For example, during a mass spectrometry experiment molecule 3 was designed to release radical ion 4. SW VJ “*0 4 a. Write a “curved-arrow" mechanism for this fragmentation. (5 points) I). Substrate 3 was used in the following oxidation reaction (you do not need to know the mechanism). How would you use mass spectrometry to tell if the reaction went to completion? Please answer with no more than one sentence. (2 points) / O)_/—/ Pd{OAc)2 O : row 0 O 0 H20 c. How would you use mass spectrometry to make sure the reaction did not lead to the aldehyde illustrated below? Be specific. (3 points) H O 3. Consider the bonds indicated with the arrows below. For each set, rank the molecules in order of decreasing wave number in an IR spectrum. Assign the molecule with the highest wave number for the indicated bond the number one, and the molecule with the lowest wave number three. [151:Iointslr 3 points each) a. Mew Me HJLMe MeOJLMe Me .3, >=NH Ma—zN Hfi—NH2 Om ...
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