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Organic Chemistry II (CHE 232-001) Examination I February 11, 2009 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 or the back of an exam page. Problem Score 1 /15 2 /35 3 /12 4 /26 5 /12 Total /1001 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. (15 pts) How would each of the following pairs of compounds differ in their IR spectra? Describe precisely the differences in IR data of the two compounds that would allow you to unambiguously distinguish between them. Be thorough but brief (no more than two sentences). (a) HC CCH2CH2CH3andH2C CCH3CH2CH2CH2CH3 The alkene will show a C=C stretch at 1650 cm-1 and a Csp2–H stretch at 3000-3150 cm-1; each of these stretches will be absent in the IR spectrum for the alkyne, which will instead contain C≡C and Csp–H stretches at 2250 cm-1 and 3300cm-1, respectively. (b) CH3CH2COOHCH3COOCH3and The carboxylic acid will show a strong and broad O-H absorption between 2500-3500 cm-1, which will be absent in the IR spectrum for the ester. It is also possible to distinguish the compounds by their carbonyl stretches: ν (CO) for RCOOH ≅ 1710 cm-1 while ν (CO) for RCOOR ≅ 1735-1745 cm-1.3 (c) The IR spectrum of a molecule known to have structure A, B, or C is shown below. Which structure is most consistent with the spectrum? Briefly, explain your reasoning. CO NH2OHCNH2COHNO2ABC A ν (C≡N) stretch at 2250 cm-1 will be present only in the IR spectrum for B.4 2. (35 pts) Describe precisely differences in the 1H NMR data of each of the following pair of compounds that would allow you to unambiguously distinguish between them. In other words, describe differences that you expect to see in 1H NMR spectra of the two compounds that would allow you to distinguish between them. Be brief (no more than two sentences). (a) OHClClOHClClABHcHbHaHcHbHa Difference: Assuming only 3-bond H-C-C-H coupling occurs, only compound A will show a singlet aromatic resonance (for Hc) in its 1H NMR spectrum (Ha and Hb will show as two doublets with J = 7-12 Hz). All of the aromatic resonances for B will at least show H-C-C-H coupling (7-12 Hz) and hence appear as two doublets and a doublet of doublets (which might be observed as a triplet if JHa-Hb = JHb-Hc). If weak 4-bond coupling is observed, Hc in A will show as doublet with J = 1-2 Hz. (b) CH2CH2ClCHClCH3CD Difference: The CH proton in C will show as a quartet (in the 4-5.5 ppm region) while the CH3 group will show as a doublet. In contrast, two triplets (one around 2.5 ppm and the other around 3.0 PPm) will be observed in the 1H NMR spectrum for D. Also, two non-aromatic resonances in 1:3 integral ratio will be observed for C and two non-aromatic resonances in 1:1 integral ratio will be observed for D.5 (c) Describe precisely the difference in the 13C NMR data of the following pair of compounds that would allow you to unambiguously distinguish between them. CH3CH3H3CCH3GH Difference: The carbon atoms exist in four different chemical environments in G while the carbon atoms exist in three different chemical environments in H. Hence G will show four total 13C resonances while H will show 3. (d) An unknown compound has the molecular formula C9H11Br. Its 1H NMR spectrum shows the following absorptions: 7.1 ppm, singlet, 2H; ! 2.3 ppm, singlet, 6H; ! 2.2 ppm, singlet, 3H. Draw the structure of the compound. Briefly, explain your reasoning. See Ace Assignment Chapter 13 and 14 – Spectroscopy, problem 16.6 (e) A molecule known to have structure A, B, C, or D shows the following absorptions in its 1H NMR spectrum: 2.32 ppm, multiplet, 2H; 3.68 ppm, triplet, 2H; 3.95 ppm, singlet, 1H; 5.75-6.35 ppm, multiplet, 2H. Its mass spectrum shows M+ and [M+2]+ peaks in a 3:1 ratio. Which structure is most consistent with the given data? Briefly, explain your reasoning. HOBrHOBrHOClHOClDABC M+ and [M+2]+ peaks in a 3:1 ratio rules out compounds that contain a Br atom. 2.32 ppm, multiplet, 2H; CH2 next to the double bond 3.68 ppm, triplet, 2H; CH2 next to OH group 3.95 ppm, singlet, 1H; OH proton 5.75-6.35 ppm, multiplet, 2H; alkene protons7 3. (12 pts) Draw a detailed mechanism for bromination of ethyl phenylacetate (1) with NBS. Explain the origin of the selectivity for formation of 2. H2COOCH2CH3NBS!, CCl4CH OOCH2CH3Br12 CH OOCH2CH3N BrOONBS!, CCl4N•OO+ Br•Br•HHCOOCH2CH3•HCOOCH2CH3•HCOOCH2CH3•Br BrCH OOCH2CH3Br+Br•repeat until terminationHCOOCH2CH3•2CHOH3CH2COCHOOCH2CH3INITIATIONPROPAGATIONTERMINATION8 4. (26 pts) Draw the major product of each of the following reactions. CH3Br2h!CH3CH3CH2HBrROORHBrCH3CH3NBS!(i)(iii)(ii)(iv)CH3CH3NBS!, ROORCH3CH3CH3BrCH3BrBrCH3CH3Brsee radical reactions assignment, question 8 Provide the reagents required for the following conversions. Write the required reagents in the box above each reaction arrow. (vi, 6pts)BrBrBrBrNBS,h!, !, or ROORBr29 5. (12 pts) Which of the two structures A and B (below) is more reasonable for a compound that has the spectral data given below? Briefly explain how the given data is consistent with the structure you picked. (a) The compound has an M+ ion at 85 amu. There is no [M+2]+ peak. (b) The only IR absorbances in the interpretable region are at 3340 and 2900 cm-1. (c) The 13C NMR spectrum shows three resonances at δ 40, 30, and 25. (d) The 1H NMR shows three resonances at δ 2.7 (m, 4H), 1.5 (m, 6H), and a broad peak at about 5.0 (1H) that changes its position with concentration and temperature. NHH2NAB The low resolution MS and 13C NMR data provided does not allow structures A and B to be unambiguously distinguished. The IR


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