Chemistry 51 Summer 2007 Final Exam

Transcription

1 Chemistry 51 Summer 2007 Final Exam 1. This is a two-hour, closed book exam. All answers are to be put on the question sheets. 2. Use the backsides of these pages for scratch paper. None other permitted. 3. At the end of the exam pass in all exam material. 4. There are 20 questions. Make sure you have all of them. All questions are worth five points. 5. Write your name on all pages of this exam. o it now! What are the products or missing reactants of the following reactions? Indicate stereochemistry and make use of templates if provided. 1. excess 1) NaN 2 2 propyne Pt 2 NBS all products 3. X 1) Li Cl NaI 2) CuX all products

2 4. what reactant to use here 1. s 4 2. NaS 3 dry Cl 5. C Br PPh 3 Na 6. excess KMn 4 cold, dilute alkaline show stereochemistry carefully!

3 7. The following mechanism is believed to occur via a chain, free radical mechanism. Write the most likely chain steps. CCl 4 Cl peroxides CCl 3 8. Give the mechanism for the following reaction. Show all important resonance structures. Use curved arrow notation. aq. acid + Et heat Et 9. Cyclohexane exists predominantly in the chair form. The boat form, another conformation, is relatively high energy. Give reasons for the higher energy of the boat form. chair, lower energy boat higher energy

4 10. Cadaverine, found in rotting flesh, has the formula 2 N(C 2 ) 5 N 2. As a forensic chemist you are given an ether solution of cadaverine and naphthalene. You wish to isolate the cadaverine and the naphthalene by means of an extraction. What are the details of your extraction technique? 11. a) Explain why para trifluoromethylphenol, on the left below, is a stronger acid than phenol on the right. > CF 3 b) The NMR spectrum of the cyclopentadienyl anion shown below indicates that all hydrogens are equivalent. Use resonance structures to explain the equivalency. C 5 5 -

5 12. Unknown compound X, C , produces no color change with acidic dichromate at 35 degrees. The 1 NMR spectrum consists of two singlets at 2.00 (1) and at 1.36 (6), a triplet at 1.06 (3), and a quartet at 2.49 (2). X is negative to the iodoform test and negative to Tollens. When X is treated with periodic acid two compounds result: A has a singlet in the NMR at 2.1 and B has a singlet at (1), a quartet at 2.27 (2) and a triplet at 1.09 (3). Give structures for A, B, and X. 13. C 2 C 2, where is deuterium, is monochlorinated and yields a mixture as shown below. Cl 2 Cl + Cl + Cl + Cl The acid component of the product mixture was analyzed by mass spectrometry. The following peaks and relative abundances were found. mass Relative Intensity Chlorine exists as two isotopes 35 Cl and 37 Cl having natural abundances of 75% and 25% respectively. a) If replacement of () were random what would be the ratio of intensities of the peak at 36 to the peak at 37?

6 b) If replacement of () were random what would be the ratio of intensities of the peak at 38 to the peak at 39? c) Assume that the reactivity of the primary atom is 1.00 and calculate the reactivity of the deuterium atom =============================================================== = Provide a synthesis of the following compounds. Use only propene as the source of all carbon atoms in the target molecules. In later problems you may also use as starting material target molecules of earlier problems even if you were not able to solve the earlier problem. o not repeat synthetic work. You may reference a compound prepared in an earlier problem by a symbol such as 14A referring to compound A in Problem propylene oxide, chloropropane 16. hexan-2-one 17. Give the mechanism for the following reaction. Show all important resonance structures. Use curved arrow notation. dimethyl ether conc I heat 2 methyl iodide

7 18. A sample of 2-bromobutane having a specific rotation of 10.0 degrees is reacted with sodium methoxide. Assume that the specific rotation of pure R 2-bromobutane is 25.0 degrees and that of pure R 2-methoxy butane is degrees. Further assume that the substitution reaction is entirely S N 2. Predict the specific rotation of the ether produced. 19.Predict the most likely cations to be observed in the mass spectrum of 4-methylpentan-2-one 20. Given below is an NMR spectrum of a compound, C Propose a structure for the compound.

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9 13 C shifts