Chem 14C Lecture 1 Spring 2017 Final Exam Part B Page 1 1. (2) Write the letter of the structure that best fits the following 13 C-NMR spectrum: 51 ppm (doublet), 44 ppm (triplet), 27 ppm (quartet), 26 ppm (triplet), and 13 ppm (quartet). Best fit =. Structure A Structure B Structure C Structure D Structure E 2. (4) In 1928 Kathleen Lonsdale used x-ray crystallography to analyze the molecular structure of hexamethylbenzene. This work is widely regarded as the first empirical proof that the benzene structure Kekulé proposed in 1862 is correct. What information regarding the molecular structure of hexamethylbenzene can be determined directly (not just inferred or implied) by x-ray crystallography? For each feature listed below write 'Y' (for yes) if this feature can be determined directly by x-ray crystallography, or 'N' (for no) if this feature cannot be determined directly. Hexamethyl benzene Planarity of the ring Number of pi electrons sp 2 carbon to sp 2 carbon bond lengths Benzene ring carbon hybridization Questions 3 13 concern these molecules: Phenol (molecule P) o-nitrophenol (molecule O) 3. (2) Rank the relative electronegativities of all atoms in o-nitrophenol (molecule O) by writing element symbols (i.e., Al or Pu) in each blank. If there is a tie write two or more elements in the same blank. Most electronegative = > > > = Least electronegative 4. (2) Complete this statement by writing a number in the blank: The molecular structure of o-nitrophenol (molecule O) includes lone pairs. 5. (2) Using the structure shown here, circle all conjugated atoms of o-nitrophenol: Page 1 score =
Chem 14C Lecture 1 Spring 2017 Final Exam Part B Page 2 6. (4) In the boxes below draw two additional o-nitrophenol (molecule O) resonance contributors. Make these contributors as significant as possible. Less significant contributors will earn less credit. 7. (3) Complete this drawing of the o-nitrophenol (molecule O) resonance hybrid. Include all lone pairs and partial pi bonds, but do not include any partial formal charges or full formal charges. You may need to consider some resonance contributors not drawn in question 6. 8. (2) Complete this sentence by writing a number in the blank: When in its most stable conformation, atoms of o-nitrophenol (molecule O) do not lie in the same plane as the benzene ring. 9. (2) In each blank write 'P' if the correct answer is phenol (molecule P), or 'O' if the correct answer is o-nitrophenol (molecule O): Has the smaller HOMO-LUMO gap: Molecule. Is more likely to be yellow and not colorless: Molecule. 10. (6) Complete the comparison of each molecular property by writing <, =, or > in the blank. For example if phenol (molecule P) and o-nitrophenol (molecule O) have equal polarity, write '=' in the polarity blank. Polarity: Phenol (molecule P) o-nitrophenol (molecule O). Boiling point: Phenol (molecule P) o-nitrophenol (molecule O). Solubility in benzene: Phenol (molecule P) o-nitrophenol (molecule O). 11. (1) Complete this statement by writing a letter (O or P) in the blank. Between phenol (molecule P; pk a 10.0) and o- nitrophenol (molecule O; pk a 7.2) the most acidic molecule is molecule. 12. (2) Write the names of two structural features (such as formal charge) that help explain the fact that the pk a of phenol (molecule P) is greater than the pk a of o-nitrophenol (molecule O). 13. (2) For the following equilibrium write > 1, = 1, or < 1 in the box above the : + K eq = + Phenol o-nitrophenol Page 2 score =
Chem 14C Lecture 1 Spring 2017 Final Exam Part B Page 3 Questions 14 16 concern molecule X: Molecule X 14. (2) Complete this statement by writing one letter in the blank. (If more than one answer is possible select the letter that best describes the relationship.) The relationship between molecule X and o-nitrophenol (molecule O) is. Answer choices: (a) Constitutional isomers; (b) conformational isomers; (c) stereoisomers; (d) enantiomers; (e) diastereomers; (f) meso compounds, and (g) none of these. 15. (3) Aromaticity is an important molecular property in pharmaceuticals and other aspects of biology. Using no more than twenty-five words, provide a concise yet precise definition of aromaticity. 16. (4) Let's decide if molecule X is aromatic. Write a number, 'Y' (for yes), or 'N' (for no) in each blank, as appropriate. Total number of pi electrons in molecule X: Does molecule X have a closed loop of p orbitals? Does molecule X obey Hückel's rule: Is molecule X aromatic? 17. (3) Draw α-d-glucopyranose in the box. Neatness and precision count. You may find it useful to practice the drawing elsewhere before drawing your final answer here. 18. (3) Complete each statement by writing one word, or part of one word, in each blank. (a) In α-d-glucopyranose, α indicates the configuration at the carbon. (b) Sucrose is an example of a saccharide whereas cellulose is an example of a saccharide. 19. (2) What is the relationship between α-d-glucopyranose and β-l-galactopyranose? Write a letter in the blank: Answer choices: (a) Enantiomers; (b) diastereomers; (c) not stereoisomers; or (d) other. 20. (2) α-d-glucopyranose tastes sweet. How does β-l-galactopyranose taste? Write a letter in the blank: Answer choices: (a) Sweeter than α-d-glucopyranose; (b) equally sweet; (c) less sweet than α-d-glucopyranose; (d) sweet but cannot tell how much; (e) sour; or (f) another answer not given here. Page 3 score =
Chem 14C Lecture 1 Spring 2017 Final Exam Part B Page 4 21. (4) Shown below are two partial lipid structures. For each case, write the name of a general lipid structure category that always includes this structure. In the Completed Structure box complete the drawing of the lipid category's general structure (not a specific example of a lipid from this category). Try to avoid using abbreviations, but if abbreviations must be used, clearly define each. Partial Structure Lipid Category Name Completed Structure (a) (b) 22. (4) Categorize each amino acid shown by writing all of the following side chain properties that apply in the Properties box: Acidic, basic, nonacidic, hydrophobic, and hydrophilic. Name Side Chain Properties (a) Serine (b) Tyrosine 23. (2) Protein structure is absolutely critical to protein function. Complete this statement by adding no more than five words. Be specific and precise. An amide bond between two amino acids in a protein influences the structure of that protein by... Page 4 score =
Chem 14C Lecture 1 Spring 2017 Final Exam Part B Page 5 24. (4) The partial DNA single helix structure shown below may have anywhere from zero to four errors. Clearly indicate (an arrow, a circle, etc.) each error your find, and add a few words of description as to why the structure is wrong (or what correction is needed). If an error occurs more than once, list it only once. If there are no errors write "no errors". Page 5 score =
Chem 14C Lecture 1 Spring 2017 Final Exam Part B Page 6 25. (33) Deduce the structure that corresponds to the spectral data on pages 6 8. 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 = 172 (M; 100%), m/z = 173 (10.24%), and m/z = 174 (32.6%). No fluorine or iodine. Write in the box the **one** formula that is consistent with the mass spectrum, and is not rejected due to other reasons. Page 6 score =
Chem 14C Lecture 1 Spring 2017 Final Exam Part B Page 7 (13) IR: IR workspace: Page 7 score =
Chem 14C Lecture 1 Spring 2017 Final Exam Part B Page 8 Anything written outside the boxes on this page will be ignored. Write only 1 H-NMR implications in the 1 H-NMR implications boxes and 13 C-NMR conclusions in the 13 C-NMR box. (10) 1 H-NMR: Chemical shift Splitting Integral # H Implications 3.54 ppm triplet 2.0 3.45 ppm singlet 1.0 1.76 ppm pentet 2.0 1.56 ppm triplet 2.0 0.95 ppm singlet 6.0 (2) 13 C-NMR: 195 ppm (singlet), 81 ppm (singlet), 79 ppm (doublet), 47 ppm (triplet), 45 ppm (singlet), 37 ppm (triplet), 34 ppm (triplet), and 24 ppm (quartet). Page 8 score =