Exam 2 - 2002

Exam 2 - 2002 - Chemistry 439 Exam II April 9, 2002 Name...

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Unformatted text preview: Chemistry 439 Exam II April 9, 2002 Name Student Number This exam consists of 100 points. 1. (25 pts) The following graph is from our discussion of the nuclear Overhauser effect. a. What is plotted on the y-axis? b. What is plotted on the x-axis? Possible choices for these two answers include: J, 3.1, M.W., x, NOE, d), (01¢, 1c, 0), o,p, SR, and bond angle. c. What is the value of “A”? d. What is the value of “B”? e. What is the value of “C”? C 23. (5 pts) If a coupling constant is found to be 15 Hz at 800 MHz. What is it at 400 MHz? 2b. (5 pts) If a peak is found at 2.0 ppm at 400 MHz, what is the chemical shift, in ppm, for this resonance at 200 MHz? 2c. (5 pts) What is one method (pulse sequence) for measuring the longitudinal relaxation times for nuclei? 3. Draw the expected COSY map for the molecule shown below. Assume that only 3- bond couplings are observed. (12 pts). 6.0 5.0 4.0 3.0 2.0 WBI' 4-bromo- 1 -butene The 1H spectrum of 4-bromo-1-butene: WW 1 w—u ‘PV‘F w.,m,.—r—v—r1r‘..... 1| | 1 I ‘ so 55 5.0 45 A.» 35 30 2.5 an LS 9.0 85 3,0 75 1,0 6.5 4. Draw a structure that is consistent with the following data (15 pts): NEAT MICRONS 15 16 17 IE IQ 2122 an " as Lu ‘000 JBDD 3600 3400 3200 3000 2300 CDCI3 200 180 Onset: 40 ppm. 160 2600 ‘ 24m 2200 2000 1500 1 500 WAVENUMBERS QE-300 MO 120 C7H140 FW 114.19 bp 128°C d 04809 $14040 100 BO 30.91 29.77' 5. The following structure has the indicated stereochemistry at carbons 1 and 4 and unknown stereochemistry at the 3 position. The COSY map is shown below along wit 1H spectrum at top and a measurement of the observed coupling constants. The 1H shi are shown at the bottom of the COSY map. The C-H correlation is on the next page. this page, b is a 1H—decoupled 13C 1D spectrum; c is, CH only DEPT, and in d, a norm DEPT showing CH and CH3 up and CH2 down. The carboxylic acid carbon is not shov in these spectra. 2.30 ppm 1.91 1,751.65 1.50 1.37 1.20 1,000.91 0.80 1.73 0950.89 Hints: Start with the 1H resonance that you would think would be most downfield (other than the COOH). What would it be coupled to? Also note that two methyls (0.91 and 0.80 ppm) are coupled to 1.75 and one methyl (0.89 ppm)is coupled to 1.37 ppm. Finally, follow resolved peaks to help finish the assignments (e.g., 1.50 ppm; it is coupled to 2.30 1.75,1:65, and 1.00 ppm). CQOH: 183.1 47.8 1.4.4» 38.9 34.7 136 32.2 29.1» 24.0 22.3 21.3 16.1 PPm Your job is to make the 1H assignments (use the table below) and draw the molecule in its correct conformation and with the correct stereochemistry. You already know that 1- methyl and 4-isopropyl are trans to each other. Use the molecule below to complete the drawing with these groups, including the —COOH, and all of the hydrogens in their correct positions (axial or equatorial) based on the data provided: axial or uatorial (if a licable) ...
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Exam 2 - 2002 - Chemistry 439 Exam II April 9, 2002 Name...

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