Organic Chemistry II (CHE ) Final Examination April 30, Name (Print legibly):

Transcription

1 rganic hemistry II (E ) Final Examination April 30, 2007 Name (Print legibly): (last) (first) PLEASE observe the following: You are allowed to have scratch paper (provided by me), and a simple model set. You do not need a calculator. Please have your student ID card present on your desk. Read through the entire exam before beginning and start first on the problems that seem easiest to you. Please provide clear and concise answers to the questions in the area provided, the back of an exam page, or on the clearly labeled spare page. Problem Score 1 /60 2 /20 3 /16 4 /60 5 /45 6 /20 Total /200

2 II

3 III

4 IV

5 1. (5 pts each, 60 pts total) Draw the major product of each of the following reactions. Do not draw mechanisms! If no reaction occurs, write N.R. (a) Sl l (b) N N( 3 ) (c) 3 3 Mg excess (d) NaB 4 P (e) N 3 2 /Pt N

6 (f) l 1. / 2, reflux (g) Sl 2 All 3 2 /Pt (h) / heat (i) 1. Ph 2 uli Mg Ph 2

7 (j) Na/ 2 P (k) 3 l N 3, 2 S 4 3 All 3 N 2 2. (5 pts each, 20 pts total) Provide the reagents needed to convert the starting materials shown into the products shown. (a) 1. Ph 3 P 2. BuLi 3. 2 (b) r 3, 2 S 4 / 2 or Na 2 r 2 7, etc. 1. NaEt (cat) (c) Et Et (d) 2 1. Sl 2 2. Et 2 N N 3

8 3. (16 points) (a) (8 pts) f the carboxylic acid derivatives shown below, circle and label the MST reactive acylating agent, AND circle and label the LEAST reactive acylating agent. l Et N 2 Most Reactive Least Reactive (b) (8 pts) Explain why cation A is much less stable than cation B. N : A Me N Me B A is not aromatic while B is aromatic. omplete delocalization in B allows for greater resonance stabilization of the cation in comparison to A. 4

9 4. (60 points) Design syntheses of the three compounds below from the indicated starting materials. Show how you would prepare each product from the indicated starting material(s). Each synthesis will require two or more steps. Show each intermediate compound and all the reagents you will need for each step. (Don t panic if you can t remember the reagents for a particular step; partial credit will be given.) Do not show reaction mechanisms. (a) starting material Forward reaction: Sl 2 KMn 4 l 1. Et 2 uli

10 (b) starting material Retrosynthesis, one possibility l + Liu 2 N Forward: 1. u 2. BuLi Liu 2 KN N 3 + Sl 2 l 1. Liu

11 (c) + starting materials Forward, 3 + Mg 1. Mg 2. 2, 3 + 7

12 4. (45 points) Draw a reasonable stepwise mechanism for each of the following reactions. Be sure that you show every bond making/bond breaking event and be sure that your use of arrows conforms to established conventions. (a) (15 pts) Me + Na, 2 Me See Textbook 8

13 (b) (15 pts) Ph N l 2 Ph N 2 l Ph Ph N Ph N N l Ph N l Ph N 2 Ph N 2 Ph N 2 l 9

14 (c) (15 points) l, l 2, 2 l 10

15 6. (20 points) (a) (10 pts) Shown below is the 1 NMR spectrum for a compound whose molecular formula is An infrared (IR) absorption for the compound is found at 1740 cm aromatic 's b 's a ' s Which of structures A-D is most plausible for the compound? Assign the 1 NMR spectrum by labeling appropriate groups of chemically equivalent hydrogen atoms in the structure that you have chosen and correlate your labels with the 1 NMR spectrum. a a 3 b b B A D 11

16 (b) (10 pts) In each problem below, choose one method (optical activity, MS, IR, 1 NMR, or 13 NMR) that will allow you to unambiguously distinguish between the two compounds. Precisely describe the difference that you expect to see in spectra of the two compounds that will allow you to distinguish between the two compounds (correct description of the difference in the spectra is worth 4 points). Be brief (no more than two sentences). (i) 2 Et 2 Et l Method for distinguishing: l A B 1 NMR Difference: nly in A does one of the aromatic protons show as a singlet. (ii) Method for distinguishing: l l D 1 or (proton-coupled) 13 NMR spectra Difference: nly in the 1 NMR spectrum of does a doublet resonance (for isopropyl methyls) and a septet (for isopropyl methine () proton) appear. nly in the proton-coupled 13 NMR spectrum of does a doublet resonance appear in the alkyl region (0-50 ppm) for isopropyl methine () carbon. 12