Chemistry 14C Fall 2015 Final Exam Part B Page 1

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1 Chemistry 14C Fall 2015 Final Exam Part B Page 1 Uric acid is a normal metabolic product derived from purine nucleosides. Gout is a painful arthritic condition in which excess uric acid precipitates as needle-like crystals in the joints, especially in the big toe. A Uric acid 1. (3) In the following list circle all of the noncovalent molecular forces that might assist the dissolving of uric acid in water. Anion-cation ydrogen bonding Dipole-dipole London forces Ion-dipole Cation-pi Pi stacking 2. (2) Circle the best prediction concerning the solubility of uric acid in water. Uric acid is highly soluble Uric acid is somewhat soluble Uric acid doesn't dissolve much at all 3. (3) By adding, subtracting, or transmuting (i.e., changing into another element) no more than four atoms, redraw the structure of uric acid so that it is even less soluble in water. 4. (6) Uric acid proton A (shown at the top of the page) has pk a = 5.4. Proton A is more acidic than proton B in the molecule shown to the right. (a) Circle the best guess for the pk a of proton B: B (b) Complete this sentence by adding no more than fifteen words. Be specific and precise. Proton A is more acidic than proton B because (2) The extent to which uric acid is ionized (deprotonated) in the bloodstream influences crystal formation. The p of blood is buffered by carbonic acid ( 2 C 3 ). + Uric acid (pk a 5.4) Bicarbonate (pk a 10) Urate (pk a 10.3) Carbonic acid (pk a 6.5) According to the given pk a data, what can we conclude about the extent of uric acid ionization in the bloodstream? Circle one: It is mostly ionized (K eq > 1) About half of the uric acid is ionized (K eq ~ 1) ot much uric acid is ionized (K eq < 1) + Page 1 score =

2 Chemistry 14C Fall 2015 Final Exam Part B Page 2 C 3 Colchicine is a medication used to relieve and prevent gout, as well as a treatment for familial Mediterranean fever. The plant source of colchicine has been used for the treatment of rheumatism and swelling since at least 1500 B.C. C 3 B C A C 3 C 3 Colchicine C 3 6. (8) Complete each sentence by writing no more than three words in each blank. Use different answers for parts (a) and (b). (a) Resonance, conjugation, and aromaticity (all resulting from p-orbital overlap) are all favorable molecular properties because all of these give the molecule and. int: Give results, not causes. (b) If colchicine rings A and C lie in the same plane, colchicine gains more and. 7. (8) Write a number in each blank. (a) ow many conjugated atoms are in colchicine? (b) ow many sp 2 oxygen atoms are in colchicine? (c) ow many lone pairs in colchicine are delocalized by resonance? (d) ow many pi electrons are in colchicine? 8. (5) Complete this sentence by circling the appropriate hybridization, then adding no more than fifteen words. Colchicine's nitrogen atom is sp 3 / sp 2 / sp because this hybridization (5) Which ring(s) of colchicine are aromatic? Complete each statement by circling 'is aromatic' or 'is not aromatic', as appropriate. If you've circled 'is aromatic' you are done with that ring. If you've circled 'is not aromatic' complete the statement by adding no more than ten words. Colchicine's A ring is aromatic / is not aromatic because... Colchicine's B ring is aromatic / is not aromatic because... Colchicine's C ring is aromatic / is not aromatic because... Page 2 score =

3 Chemistry 14C Fall 2015 Final Exam Part B Page (2) In box A below draw another significant resonance contributor for colchicine. Less significant contributors will earn less credit. 11. (3) In box B below complete the colchicine resonance hybrid by adding all partial pi bonds. Do not include any δ + or δ charges. C 3 C 3 C 3 C 3 C 3 Box A - Resonance contributor Box B - Resonance hybrid 12. (4) Colchicine has just one sp 3 stereocenter. Circle one answer from each set. (a) This stereocenter is: S R either Cannot determine Does not apply (b) Colchicine's optical activity is: (+) (-) either Cannot determine Does not apply 13. (4) Complete this statement by writing one number in each blank. The colchicine structure shown at the top of exam page 2 has enantiomer(s) and diastereomer(s). 14. (2) Between colchicine and all its stereoisomers included in question 13, how many are useful for the treatment of gout? Circle an answer: Cannot determine The remaining questions on this exam have nothing to do with uric acid, gout, or colchicine. 15. (2) Provide a concise definition (use no more than fifteen words): Lipid 16. (3) Draw the structure of a monounsaturated fatty acid likely to be found in humans. 17. (6) (a) ame the three motifs that comprise the secondary structure of proteins. (b) Two of these motifs utilize intramolecular hydrogen bonds. What atom is attached to the hydrogen in the hydrogen bond donor portion of each of these hydrogen bonds? Circle one: F C S (c) Circle the -bond acceptor among these intramolecular protein hydrogen bonds: C= C=C Page 3 score =

4 Chemistry 14C Fall 2015 Final Exam Part B Page (32) Deduce the structure that corresponds to the spectral data on pages 4 6. Write your final answer in the box. A correct answer is worth full credit. If the answer is incorrect, your analysis of the spectra can be worth significant partial credit, so show your work clearly in the space below each set of data only. Answers outside of these places will be ignored. Final Structure Box (4) Mass spectrum: m/z = 143 (M; 100%), m/z = 144 (9.62%) and m/z = 145 (less than 1%). o fluorine or iodine. Mass spectrometry workspace: Write in the box the one formula that is consistent with the mass spectrum, and is not rejected due to other reasons. Page 4 score =

5 (13) IR: Chemistry 14C Fall 2015 Final Exam Part B Page 5 IR workspace: Page 5 score =

6 Chemistry 14C Fall 2015 Final Exam Part B Page 6 Write only 1 -MR implications and 13 C-MR conclusions in the boxes. Anything written outside the boxes on this page will be ignored. (10) 1 -MR: Chemical shift Splitting Integral # Implications 3.52 ppm singlet ppm quartet ppm quartet ppm triplet ppm triplet 3.0 (2) 13 C-MR: ppm (singlet), 64.1 ppm (triplet), 51.5 ppm (triplet), 34.8 ppm (triplet), 13.0 ppm (quartet), and 7.6 ppm (quartet). 13 C-MR conclusions: Page 6 score =