<p>CHM 251 Organic Chemistry I Fall Homework #3 Due: Tuesday, November 4, 2008 by 5:00 pm</p><p>Directions: Print this document and hand in your answers directly on the pages provided. No extra pages should be attached!</p><p>Problem #1 Coupling of hydrogens in the proton NMR can come in a variety of forms: geminal, vicinal (3- bond), W coupling, through a pi network (4-bond and even 5-bond), and through space. In the following structure, all of the hydrogen atoms have been labeled (using the template provided). Using the labeling, complete the table below. For typical coupling constant values, see pages 62, 71, 72, and 73 of “SAM.” You can also consult pages 786-787 of Jones.</p><p> k</p><p>H H</p><p>Types of coupling: Saturated vicinal Unsaturated vicinal (cis) Unsaturated vicinal (trans) 4-bond or 5-bond pi network W coupling Ortho, meta, para aromatic Saturated geminal Unsaturated geminal</p><p>Hydrogen Label Coupling Type of Coupling Typical Coupling partner Constant (J value)</p><p>Ha Hb</p><p>Hb Hc</p><p>Ha Hc</p><p>Hd He</p><p>Hd Hf</p><p>He Hf</p><p>Hf Hg</p><p>Hg Hh</p><p>Hi Hj</p><p>Hi Hk Hk Hn</p><p>Hn Hp</p><p>Hn Hm</p><p>Hh Hm</p><p>Hk Hp</p><p>Problem #2 Shown below is a fragment of a 60 MHz 1H-NMR spectrum for 2-furoic acid – only the resonances for the three aromatic protons are shown.</p><p>Hx Hm</p><p>CO2H O HA</p><p>(a) Is 2-furoic acid aromatic? Explain. (b) Convert the shift data in Hz to chemical shifts in ppm. (c) Extract all relevant coupling constants by direct measurement (use a ruler). (d) Draw a splitting diagram to account for the complex splitting patterns that appear in the spectrum below. Problem #3 Answer the following questions with regard to the labeled structure of ranitidine (Zantac, antiulcerative) shown below. B</p><p>C NO2 E</p><p>H3C S O NH CH3 Ranitidine D A</p><p>(a) How many chemically (and/or magnetically) unique protons are present in ranitidine?</p><p>(b) What is the expected integration ratio for the protons in ranitidine?</p><p>(c) How many unique peaks should be present in a proton decoupled (normal) carbon NMR spectrum of ranitidine?</p><p>(d) Indicate the approximate expected chemical shift for the protons labeled A.</p><p>(e) Indicate the approximate expected chemical shift for the carbon labeled B.</p><p>(f) Indicate the expected splitting pattern (singlet, doublet, etc.) for the proton labeled C.</p><p>(g) Indicate the expected splitting pattern (singlet, doublet, etc.) for the proton labeled D.</p><p>(h) Indicate the expected splitting pattern (singlet, doublet, etc.) and approximate size of the coupling constant for the protons labeled E. Problem #4 Imagine that you were given a 4.00 mL of a 1.50 M solution of an enantiomerically pure sample of (R)--methylbenzylamine. The observed optical rotation for this compound has been determined to be +5.45° in a 10 cm sample container.</p><p> c is in g/mL l is in dm</p><p> a. What is the molar mass of (R)--methylbenzylamine?</p><p> b. What is the specific rotation of (R)--methylbenzylamine?</p><p> c. What is the observed rotation if this solution is mixed with an equal volume of a 1.50 M solution of enantiomerically pure (S)--methylbenzylamine? </p><p> d. Why do you observe this rotation?</p><p> e. What is the observed rotation if the original 1.50 M solution of (R)-- methylbenzylamine is diluted with an equal volume of solvent?</p><p> f. What is the specific rotation of (R)--methylbenzylamine after the dilution described in part (e)?</p><p> g. What is the specific rotation for a sample of pure (S)--methylbenzylamine? h. What is the observed optical rotation of a 10 mL solution that contains 0.04 mole of (R)--methylbenzylamine and 0.1 mole of (S)--methylbenzylamine (assume a 10 cm path length)?</p><p> i. Given the specific rotations of (R)--methylbenzylamine and (S)-- methylbenzylamine (determined above), what is the optical purity and % composition of a mixture whose observed rotation was found to be -15.00o?</p><p> j. Sketch what you think the 1HNMR spectrum of this mixture (from part i) would look like using (S)-(+)-O-acetylmandelic acid as the resolving agent (present in the NMR tube with your mixture of enantiomers).</p><p> k. How does this compare with the resolution that you achieved in Organic Chemistry Laboratory Experiment #6? Explain. Problems #5 and #6 Determine a valid Lewis Structure that is consistent with the spectroscopic data appended to the assessment page on the organic chemistry web site. NOTE: there are 2 problems here and you are to complete both of them. Be sure to provide a complete analysis as described in class for problems #16 and 51. Your analysis should describe HOW you used the data to arrive at your structure. Be sure to print BOTH problems and feel free to annotate directly on the spectral data.</p><p>Explanation for Problem #5: Explanation for Problem #6:</p>