Organic Chemistry II* (CHE 232-002) Examination I March 1, 2007 Name (Print legibly):________KEY________________ (last) (first) Student ID#: _________________________________ PLEASE observe the following: You are allowed to have scratch paper (provided by me), and a simple model set. You do not need a calculator. Please have your student ID card present on your desk. Read through the entire exam before beginning and start first on the problems that seem easiest to you. Please provide clear and concise answers to the questions in the area provided, the back of an exam page, or on the clearly labeled spare page. Problem Score 1 /10 2a-d /10 3a-l /52 4 /12 5a-b /12 6a-d /16 7 /8 Total /1 TABLE OF ATOMIC WEIGHT MULTIPLES. C1 12 O1 16 C2 24 O2 32 C3 36 O3 48 C4 48 O4 64 C5 60 O5 80 C6 72 O6 96 C7 84 C8 96 N1 14 C9 108 N2 28 C10 120 N3 42 C11 132 N4 56 C12 144 N5 70 C13 156 C14 168 C15 180 C16 192 35Cl1 35 79Br1 79 35Cl2 70 79Br2 1582 1. (10 pts) Enter the letter of the best answer in the space provided. __c__ (a) This molecule cannot participate as a reactant in a Friedel-Crafts reaction. a. Benzene d. Toluene b. Chlorobenzene e. t-Butylbenzene c. Nitrobenzene __c__ (b) Which of the following compounds would you expect to be the most reactive toward ring nitration? a. Benzene d. p-Xylene b. Toluene e. Benzoic acid c. m-Xylene __e__ (c) Which of the following electrophilic aromatic substitution reactions is reversible? a. Friedel-Crafts acylation d. Nitration b. Chlorination e. Sulfonation c. Nitration __a__ (d) Undesired polysubstitution of an aromatic ring is most likely to be encountered in the case of a. Friedel-Crafts alkylation d. Sulfonation3 b. Friedel-Crafts acylation e. Chlorination c. Nitration 2. (10 pts) Which of the following species is/are aromatic? (Circle the aromatic Species) Aromatic species are shown in red4 NH::N H5 3. (4 points each, 52 points total). Draw products of the reactions below. If no reaction occurs, write N.R. H2SO4NO2(a)OCH3SO3Br(b)CH3MeNHEt. ButONaPd(0), phosphineBr2CCl4CH3HNO3/H2SO4Cl2FeCl3(c)(d)(e)KMnO4OH-, reflux (heat)CH3CH2CH3(f)Br2FeBr3NO2(g)CH3O2N+CH3NO2ClN.R.COO-COO-(accept diacid for full credit)NO2OCH3SO3HNMeEtH3CSnHClNO2BrNH2Br6 CH3(h)IPd(0), phosphineCH3H3COMeBOHOHCH3CH3CH3ClAlCl3AlCl3CH2CH2NO2H3C COCl(i)(j)Na/NH3OCH3Br2, excessNH2(k)(l)+H3CCH3CH3MeOOCH3NH2BrBrBrCH2CH2NO2OH3CCH2CH2NO2+N.R.OCH37 4. (12 points) Draw a mechanism, using arrows, for the reaction of chlorobenzene with nitric acid in concentrated sulfuric acid. First, show the mechanism for the formation of the electrophile then show the mechanism when the electrophilic attack is at the para position. Show all possible resonance forms of the arenium ion formed by para attack. Include the final step of conversion of the arenium ion to the product in your mechanism ClHNO3/H2SO4ClNO2ClNO2+ HO NO2+ H3O+H2O+NO2+ H2O+NO2 + H2OH2SO4 H3O+ + HSO4-H2O ClH NO2ClH NO2ClH NO2ClH NO2:::::Cl+NO2: ::HSO4-ClNO28 5. (12 points) Starting from benzene, show how you would make compounds 1 and 2 cleanly in more than one step. Note: a clean reaction essentially produces only one product. There is no need to show mechanisms for this question. (a) 1 Several approaches possible including (b) 2Cl Several approaches possible including9 6. (16 pts) In each problem below, choose one method (optical activity, MS, IR, 1H NMR, or 13C NMR) that will allow you to unambiguously distinguish between the two compounds. Precisely describe the difference that you expect to see in the spectra of the two compounds that will allow you to distinguish between the compounds (correct description of the difference in the spectra is worth 3 points). Be brief (no more than two sentences). (a) OHClClClOHClClClAB Method for distinguishing: 1H NMR Difference: A will show two singlet resonances in the aromatic region of its spectrum while B will show two doublet resonances in the aromatic region of its 1H NMR spectrum. (b) OHClOHBrCD Method for distinguishing: Mass spectrometry Difference:10 C and D have different molar masses hence and hence can be differentiated on the basis of the M+ ion observed. Also, C will show a peak for its [M+2]+ ion whose intensity is 33% that of the M+ ion while D will show a peak for its [M+2]+ whose intensity is equal to that of the M+ ion (c) OHOHE F Method for distinguishing: 1H NMR and/or proton-coupled 13C NMR Difference: The 1H NMR spectrum of E will show two triplet resonances in 1:1 integral ratio for its two chemically inequivalent methylene (CH2) units while the 1H NMR spectrum of F will show a doublet- and a quartet resonance in 3:1 integral ratio for its methyl and methine protons, respectively. Proton-coupled 13C NMR will similarly show two triplet resonances for the two chemically inequivalent methylene carbons in E while a quartet- and doublet resonance will be observed for methyl and methine carbons of F, respectively. (Note: both compounds should the same number of resonances for phenyl protons and carbons). (d) A compound has the formula C8H9Br. Its 1H NMR spectrum consists of a 3-hydrogen doublet at 2.0 ppm, a 1-hydrogen quartet at 5.15 ppm, and a 5-hydrogen multiplet at 7.35 ppm. Which is a possible structure for the compound? Assign the 1H NMR data.11 BrCH2CH3H3CCH2BrCH2CH2BrCHBrCH3CH3BrCH3IIIIIIVIV CHBrCH3V! 2.0! 5.15 The aromatic hydrogens show at 7.35 ppm 7. (8 points) A compound of molecular formula C15H24O has the spectral data below. Deduce a reasonable structure for the compound and briefly explain how the given data is consistent with your proposed structure. Mass spectrum: m/z = 220, 205, 57; IR (Nujol): 3660 cm-1 (m, sharp). 1H NMR (CDCl3): δ 1.43 (s, 18H), 2.27 (s, 3H), 5.00 (s. 1H), 6.98 (s, 2H). [Signal multiplicity and number of protons shown in parenthesis] 13C NMR (CDCl3): δ 21.2 (q), 30.4 (q), 34.2 (s), 125.5 (d), 128.2 (s), 135.8 (s), 151.5 (s) The two structures most consistent with the above data are: OHCH3(H3C)3CC(CH3)3CH3OH(H3C)3CC(CH3)3orA B The mass spectral data is consistent with the molecular formula and suggest the presence of methyl (220-205 = 15) and butyl
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