A Grignard reagent formed would deprotonate H of the ethyl alcohol OH.

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Willis Walters
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1 216 S11-E2 Page 2 Name Key I. (9 points) Answer in the boxes below the following questions for the Grignard reagent C 3 -Mg. (1) (2 points) Is the carbon atom associated with magnesium electrophilic or nucleophilic? electrophilic nucleophilic [circle one] (2) (3 points) Explain why the Grignard reaction has to be carried out in an anhydrous solvent. The Grignard reagent produced would be destroyed by the reaction with water present in a non-anhydrous solvent. (3) ( points) Write the conjugate carbon acid (i.e., C-) of the C 3 Mg and explain why Grignard reagents are strong bases. structure: C explanation: The pka of C is ca. 0. Therefore, its conjugate base is highly basic. II. (6 points) Ethyl alcohol (C 2 ) quite often is present in technical-grade diethyl ether. If this grade of diethyl ether were used, what effect, if any, would the ethyl alcohol have on a Grignard reagent used? Explain using a chemical equation using methylmagnesium bromide as an example. explanation based upon the reaction mechansim: A Grignard reagent formed would deprotonate of the ethyl alcohol. C 2 C 3 R Mg C 2 C 3 R Mg III. (8 points) For each of the reactions below, draw in the boxes provided the structure of the expected major organic product. (1) 1. Mg (1.1 mol equiv) ether 2. C 3 C 3 (1.1 mol equiv) aq N Cl (acidic workup) enantiomer (2) Mg (1.1 mol equiv) ether aq N Cl (acidic workup) C 3 Mg enantiomer

electrophilic nucleophilic [circle one] (2) (3 points) Explain why the Grignard reaction has to be carried out in an anhydrous solvent.

2 216 S11-E2 Page 3 Name Key IV. (16 points) For the following reaction sequence, draw the correct structures in the boxes provided. Ph 3 P: (C 18 1 P) C 3 benzene, reflux Ph 3 P C 3 trans "salt" NaC 2 /C 2 C 3 major isomer: C Ph 3 P C 3 cis dichloromethane room temperature C P (ylide) Na C 2 C 3 minor isomer: C note: Ph = C 6 Ph 3 P= V (12 points) Show how many peaks you would expect to observe in the proton-decoupled 13 C NMR spectrum of each of the following compounds. Indicate your answers in the boxes provided. (1) C 3 -C 3 C chiral center! (2) (3) S N 3 S C cis () () C C C 2 C 2 6 C C 180 rotation (6) 3 C 3 C C 3 C 3

(ylide) Na C 2 C 3 minor isomer: C 12 12 note: Ph = C 6 Ph 3 P= V (12 points) Show how many peaks you would expect to observe in the proton-decoupled 13 C NMR

3 216 S11-E2 Page Name Key VI. ( points) The proton NMR spectrum of a mixture of acetonitrile (C 3 C N), methylene chloride, (C 2 Cl 2 ) and benzene (C 6 6 ) is integrated and results in step heights of 1, 6, and 18 mm for the signals at δ 2.10,.30, and 7.26 ppm, respectively. In what mole ratio are the three substances present? No explanation required. No partial credit will be given to this problem. acetonitrile : methylene chloride : benzene = : 3 : : : VII. (8 points) For each of the reactions given below, draw in the box the structure of the expected product. Make sure to indicate the stereochemistry of the product whenever applicable. (1) C 3 C 2 Cl 2 (solvent) room temperature C 3 endo product enantiomer (2) 3 C C 2 Cl 2 (solvent) room temperature C 3 endo product or C 3 enantiomer VIII. (10 points) Provide in the box below a step-by-step, curved-arrow mechanism for the formation of hydroxy acid 2 from diketone 1. Make sure to include the mechanism for the acidic workup as well. K ( mol equiv) 2 reflux 3 to p = mech arrows: 1 pt 1 This is fine, too. 1 mech arrows: 2 pts mech arrows: 1 pt mech arrows: 1 pt mixture of stereoisomers here interm str: 1 pt each mech arrows: 1 pt 2

signals at δ 2.10,.30, and 7.26 ppm, respectively. In what mole ratio are the three substances present? No explanation required. No partial credit will be given to this problem.

4 216 S11-E2 Page Name Key

5 216 S11-E2 Page 6. Name IX. (continued) A B C D E F G X. (1 points) n the basis of its spectroscopic information provided below, propose the structure for the compound, C 12. Draw the proposed structure in the box on page 7 and give a brief explanation as to how the structure is deduced from the spectroscopic information provided.

6 Structure: 3 C C C C 3 3 C diastereotopic methyls chiral center! 0 unit of unsaturation Explanation (just assign the IR peak at 3368 cm -1 and all -1 peaks right next to the corresponding functional group/-1 nuclei): 0.92 ppm (doublet) 0.88 ppm (doublet) 3 C 3 C C 3. ppm (multiplet) C 1.6 ppm (octet) C cm ppm 1.3 ppm (doublet) 10

peaks right next to the corresponding functional group/-1 nuclei): 0.

7 216 S11-E2 Page 8 Name Key XI. (1 points) n the basis of its spectroscopic information provided below, propose the structure of the compound, C Draw the proposed structure in the box on page 9 and give a brief explanation as to how the structure is deduced from the spectroscopic information provided. Make sure to assign all proton and C-13 NMR peaks.

8 216 S11-E2 Page 9 Name Key XI. (continued) Structure: 3 C C 3 3 C C 2 C 3 C 3 C 2 C 3 C 2 C 2 C 3 C 3 3 C C 2 C 3 3 C C 2 C 3 These should show only one sp 2 alkene C-13 peak. => -1 point Explanation (just assign the strongest IR peak and all -1 and C-13 peaks right next to the corresponding functional group/-1, C-13 nuclei): Units of unsaturation: 3; only 6 C-13 peaks! 22 ppm 2.0 ppm 3 C 12 ppm 16 ppm 172 cm -1.2 ppm C 2 C 3 60 ppm 1 ppm 1.2 ppm 2.0 ppm 3 C 172 cm ppm C 2 C 3.2 ppm 1 ppm 10

The Four Questions to Ask While Interpreting Spectra. 1. How many different environments are there?

The Four Questions to Ask While Interpreting Spectra. 1. How many different environments are there? 1 H NMR Spectroscopy (#1c) The technique of 1 H NMR spectroscopy is central to organic chemistry and other fields involving analysis of organic chemicals, such as forensics and environmental science. It