216 S10-Exam #2 - Page 2. Name______________________ I. (14 points) The Grignard reagent C6H5-MgBr is prepared from bromobenzene (C6H5-Br) and Mg. Answer in the boxes below the following questions. (1) (2 points) Is the carbon atom associated with the bromine atom in bromobenzene electrophilic or nucleophilic? electrophilic nucleophilic[circle one] (2) (2 points) Is the carbon atom associated with magnesium in the Grignard reagent electrophilic or nucleophilic? electrophilic nucleophilic[circle one] (3) (2 points) Is the magnesium atom oxidized or reduced during the formation of the Grignard reagent? oxidized reduced[circle one] (4) (4 points) Explain why the Grignard reaction has to be carried out in an anhydrous solvent. (5) (4 points) Write the conjugate carbon acid (i.e., C-H) of the C6H5–MgBr and explain why Grignard reagents are strong bases. structure:explanation: II. (6 points) Ethanol [CH3CH2OH] is often present in technical-grade diethyl ether. If this grade of diethyl ether were used, what effect, if any, would the ethanol have on a Grignard reagent used? Explain through the use of a chemical equation using C6H5–MgBr as an example. explanation based upon the reaction mechansim:216 S10-Exam #2 - Page 3. Name_________________________ III. (11 points) Treatment of cyclohexene with bromine produces trans-1,2-dibromocyclohexane as a racemate. In spite of its simple structure, it shows quite complex spectra, particularly the 1H NMR spectrum. BrBrHaHbHjHdHcHiHgHhHfHe+ Br2 (1) (2 points) How many different 13C NMR peaks would you expect from this dibromide? ________ (2) (9 points) Identify the indicated pairs of hydrogens in the dibromide as (i) homotopic, (ii) enantiotopic, or (iii) diastereotopic Hs. Write the answers as (i), (ii), or (iii). Ha and Hb _______ Hc and Hd _______ He and Hf _______ Hg and Hh _______ Hi and Hj _______ Hc and Hi _______ Hd and Hj _______ He and Hg _______ Hf and Hh _______ IV. (14 points) Show how many peaks you would expect to observe in the proton-decoupled 13C NMR spectra of the following compounds. Indicate your answers in each of the boxes provided. (2)(4)(5)(6)(1)(7)CH3H3CNHNCH3CH3O(3)-OOCNH3+OCH3OCH3CH3CH3H3CH3C(room temperature)OOCH3CH3H3CH3CO V. (5 points) The pKa value of the NH of CH3NH2 is about 35. In contrast, the pKa value of NH of urea [(H2N)2C=O] is about 12. Provide an explanation in the box below as to why the NH of urea is considerably more acidic than that of methylamine. If your explanation involves the resonance concept, make sure to draw a relevant resonance structure(s). 5216 S10-Exam #2 - Page 4. Name________________________ VI. (25 points) For each of the following two reactions, draw in the box the structure of the expected product from the reaction shown and provide in the box a reasonable step-by-step mechanism using the curved-arrow convention that accounts for its formation. You need not show the mechanism for the protonation step in (2). (1) (11 points) [J. Am. Chem. Soc. 2010, in press] OO POOCH2CH3PhPhPhHnote: Ph = C6H5POPhPhPh+ +CH2Cl2 (solvent)room temperature4Mechanism:OO7 (2) (14 points) OOOOC10H6O44NaOCH3HOCH3 (solvent)refluxH3O+ workupC11H10O5Mechanism:10OOOO216 S10-Exam #2 - Page 5. Name________________________ VII. (20 points) For each of the following reactions, draw in the box provided the structure of the expected product. OCH3endo productOOO+CH2Cl2(solvent)room temperature(1)endo product+ enantiomer+CH2Cl2(solvent)room temperature(2)HOCH3H3CO44(3)endo product+ enantiomer+CH2Cl2(solvent)room temperature4OONCH3H(4)HOCH3(solvent)room temperature4HOCH3O+ H2ONaOCH3C11H16O(5)+HOCH2CH3(solvent)4HOOOOCH2CH3OCH2CH3NaOCH2CH3C14H16O4+ H2O216 S10-Exam #2 - Page 6. Name________________________ VIII. (12 points) On the basis of its spectroscopic information provided below, answer the questions given on page 7 and draw the structure of the compound (C9H12O) in the box on page 7. IR (liquid film) 1H NMR spectrum in CDCl3 13C NMR data (in CDCl3): δ 32.06, 34.15, 61.85, 125.79, 128.35, 128.39, and 141.91 ppm216 S10-Exam #2 - Page 7. Name_______________________ VIII. (continued) (1) (1 points) What is (are) the unit(s) of unsaturation of this compound? _____________ (2) (1 point) Does this compound have a benzene ring? Yes No (circle the one that applies) (3) (1 point) What does the IR spectrum tell you in terms of the presence of an O-containing functional group in this molecule? _____________ (4) (4 points) What is the structure of this compound? (no partial) 4 (5) (5 points) Draw in the box below the structure you showed above and assign all 1H peaks in the 1 – 4 ppm range and the 13C peak at 61.85 ppm to the corresponding H and C nuclei in the proposed structure. 5 IX. (13 points) On the basis of its spectroscopic information provided below, answer the questions given on page 8 and draw the structure of the compound (C7H14O) in the box on page 8. C7H14O: IR (liquid film) 2958 - 2872 (several strong peaks), 1719 cm-1 (strong). 1H NMR (CDCl3) δ 0.890 (d, 6H, J = 7.1 Hz), 1.359 (quartet, 2H, J = 7.1 Hz), 1.435 (nonet,* 1H, J = 7.1 Hz), 2.137 (s, 3H), and 2.418 (t, 2H, J = 7.1 Hz) 13C NMR (CDCl3) δ 22.36, 27.73, 29.79, 32.72, 41.82, 209.22 ppm note: *nine peaks216 S10-Exam #2 - Page 8. Name_______________________ IX. (continued) (1) (1 points) What is (are) the unit(s) of unsaturation of this compound? _____________ (2) (1 point) What do the IR spectral data tell you in terms of the presence of an O-containing functional group in this molecule? _____________ (3) (1 points) What do the 13C NMR spectral data tell you in terms of
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