Organic Chem II Spring 2008 Exam 1

Organic Chem II Spring 2008 Exam 1 - - PR EME D41 1.C OM P...

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Unformatted text preview: - PR EME D41 1.C OM P - PR EME D41 1.C OM CHM 202 Exam 1 Key. Answers on last page. 1. Principle fragmentation of the molecular ion of 2,3-dimethyl-3-pentanol would be expected to produce how many peaks in the mass spectrum? b. 3 c. 4 d. 5 e. 6 OM a. 2 - PR EME D41 1.C OM In other words, how many observable peaks does the molecular ion itself produce when it fragments (we’re not concerned here with subsequent fragmentation of smaller fragments, nor with the molecular ion peak itself). b. 87 c. 98 d. 101 e. 116 COM a. 73 - PR EME D41 1.C 2. Referring to the prior question, which the heaviest m/z peak expected to be observed due to direct fragmentation of the molecular ion? - PR EME D4 11. 3. Principle fragmentation of the molecular ions o f 3-methyl-3-chlorohexane would be expected to produce how many peaks in the mass spectrum? b. 5 c. 6 d. 7 e. 8 COM a. 4 - PR EME D4 11. COM In other words, how many observable peaks do the molecular ions themselves produce when they fragment (we’re not concerned here with subsequent fragmentation of smaller fragments, nor with the molecular ion peaks themselves). b. 93 c. 99 d. 105 e. 107 COM a. 91 - PR EM ED4 11. 4. Referring to the prior question, which the lightest m/z peak expected to be observed due to direct fragmentation of the molecular ions? - PR EM ED4 11. 5. An organic compound gives an M+ peak at m/z 122 and a peak of nearly equal intensity at 124. ⋅ What is a likely molecular formula for the compound? b. C8H12 N c. C3 H7Cl d. C3 H7Br e. C3H8 Br ED4 11. COM a. C8H10 O - PR EM ED4 11. COM - PR EM 6. Which of the following structures is consistent with the following data: MS: molecular ion at m/z 58 IR: 1710 cm-1 (strong) 1 H NMR: δ 2.1; singlet (only signal observed) b. CH3CCH3 O c. CH3CH2CH d . 2-methylpropane ED4 11. COM a. butane O - PR EM 7. Which of the following statements about IR spectroscopy is not true? MED 411 .CO MPRE M ED4 11. COM a. a C-H stretch occurs at a greater wavenumber than a C-H bend b. a the C-H stretch in C=C-H occurs at a greater wavenumber than the C-H stretch in C≡C-H c. A C=O stretch occurs at a greater wavenumber than a C=C stretch d. A C=N stretch occurs at a greater wavenumber than a C– N stretch e. A C=O stretch occurs at a greater wavenumber than a C– O stretch PRE D. Heller 1 OM 1.C D41 - PR EME - PR EME D41 1.C OM For each of the following compounds indicate the number of 1H NMR or 13C NMR signals you would expect to see (ignoring splitting and assuming no overlap of signals). b.1 c.2 d.3 1.C d.5 D41 c.4 e.6 e.4 c.8 11. b.7 - PR EME D4 a.6 or less Br Cl N e.10 or more N COM C NMR d.9 b.7 c.8 d.9 e.10 or more c.5 d.6 e.7 COM a.6 or less - PR EME D4 11. 13 Cl COM 10. 1 H NMR 11. Br - PR EME D41 a.0 OM C NMR 1.C 13 9. b.3 - PR EME a.2 OM 8. 1 H NMR ED4 11. 12. 1 H NMR b.4 OH O ED4 13 C NMR OH b.4 c.5 d.6 e.7 b.5 c.6 d.7 e.8 or more b.5 c.6 d.7 e.8 or more - PR EM ED4 11. COM a.3 - PR EM 13. 11. COM - PR EM a.3 a.4 C NMR COM 13 a.4 MED 411 .CO MPRE M ED4 11. COM - PR EM ED4 11. 15. - PR EM ED4 11. COM 14. 1H NMR PRE D. Heller 2 O OM 1.C D41 - PR EME D41 1.C OM 16. How many distinct triplets would you expect in the 1H NMR of the compound below? Note: recall that we are ignoring coupling due to hydroxyl protons because of proton exchange. OH b. 2 c. 3 - PR EME a. 1 D41 1.C OM - PR EME HO d. 4 e. 5 or more O - PR EME D41 IR: broad peak in 2500-3000 cm-1 region. strong peak at 1715 cm-1 11. COM Mult. triplet multiplet triplet singlet O COM b. OH O c. O d. OH OH Br e. O Br OH OH Br - PR EME D4 Br 11. Br a. #H 3 2 1 1 - PR EME D4 δ 1.08 2.07 4.23 10.97 1.C OM 17. Identify compound C4H7 BrO2, with 1 H NMR data as shown. 11. COM 18. Identify compound C15H14O, with 1 H NMR data as shown. ED4 IR: strong peak at 1720 cm-1 Mult. singlet singlet multiplet COM - PR EM ED4 11. COM #H 3 1 10 - PR EM δ 2.20 5.08 7.25 b. O e. c. - PR EM ED4 11. a. O d. O O ED4 11. COM O 11. COM - PR EM + 19. An organic compound gives an M⋅ peak at m/z 73 and a b ase p eak at m/z 58. The 1 H NMR data shows two singlets: δ1.3 (broad, 2H); δ1.2 (9H). What is a likely structure for the compound? - PR EM ED4 a. c. N H2 NH N H2 ED4 MPRE M .CO 411 MED PRE D. Heller e. d. 11. COM NH2 b. 3 OH OM 1.C D41 - PR EME b. c. O O d. 1.C O OM - PR EME D41 O e. H OM O - PR EME a. D41 1.C OM 20. Compound C5 H8 O has a strong IR absorption at 1745 cm-1. DEPT 13C NMR: δ220 (C), δ39 (CH2), and δ23 (CH2). Identify the compound. I. I II. COM - PR EME D4 I I. 11. COM - PR EME D41 1.C 21. Three compounds, A, B, and C, have the same molecular formula, C5 H6. Compounds B and C have an IR absorption at roughly 3300 cm-1; compound A has no absorption in that region. Compounds A and B show a UV-Vis λmax near 230 nm. Compound C shows no absorption maximum beyond (i.e., higher than) 200 nm. Propose structures for A, B, and C. 11. COM - PR EME D4 11. a. A = I; B = II; C = III b. A = II; B = I; C = III c. A = II; B = III; C = I d. A = I; B = III; C = II e. A = III; B = II; C = I - PR EM ED4 22. Which of the following is not a true statement? COM - PR EM ED4 11. COM a. A π to π* transition has a smaller lambda max (λmax) than an n to π* transition. b. A chromophore is the part of a molecule responsible for a UV/Vis spectrum. c. Ultraviolet light is higher in energy than visible light. d. Conjugation raises the energy of the LUMO and lowers the energy of the HOMO. e. More energy is required for a π to π* transition than for an n to π* transition. 23. The 1 H NMR o f the following compound would be expected to exhibit: ED4 11. O two singlets at around δ2.1 with a relative area of 6:4 a singlet and a triplet at around δ3.3 with a relative area of 6:4, respectively a singlet and a triplet at around δ2.1 with a relative area of 3:2, respectively two singlets at around δ3.3 with a relative area of 3:2 a singlet and a quintet at around δ2.5 with a relative area of 6:4 O - PR EM ED4 11. COM - PR EM a. b. c. d. e. - PR EM a quintet and a triplet with a relative area of 2:1, respectively a quintet and a triplet with a relative area of 1:2, respectively two triplets with a relative area of 2:1 a triplet of triplets and a triplet with a relative area of 9:3 M, M + 2 and M + 4 peaks in the relative ratio of 1:2:1 MED 411 .CO MPRE M ED4 11. COM a. b. c. d. e. ED4 11. COM 24. The 1 H NMR o f the following compound would be expected to exhibit: PRE D. Heller 4 Br Br OM 1.C D41 - PR EME 1.C OM 25. Identify the compound, C3H4Br2, with 1 H NMR data as shown. δ 4.2 5.6 6.0 multiplicity singlet singlet singlet D41 1.C OM - PR EME D41 #H 2 1 1 Br Br Br b. c. Br 1.C or Br Br Br Br - PR EME D41 Br Br d. Br or OM Br - PR EME a. - PR EME D4 11. COM e . m ore th an o n e o f t he ab ov e i s co ns i st en t wi t h th e d at a 11. COM 26. Which of the following protons would be expected to give an NMR signal with the highest chemical shift value (farthest downfield)? 2 b. 2 4 5 c. 3 d. 4 e. 5 - PR EM ED4 11. a. 1 3 COM 1 - PR EME D4 (CH3)2CH O CH2CH2 CH3 11. COM 27. Which of the following would increase the UV/Vis absorbance of a solution of phenol (C6 H5OH) in ethanol? increasing the amount of phenol in the solution decreasing the amount of ethanol in the solution decreasing the light path through the solution both a and b both b and c ED4 11. COM - PR EM ED4 a. b. c. d. e. - PR EM ED4 11. COM I. C-H C-H C-D C-D II. presence or absence of a stretch at around 1600 cm-1 presence or absence of a stretch at around 3300 cm-1 presence or absence of a stretch at around 1600 cm-1 presence or absence of a stretch at around 3300 cm-1 2. d 14. e 26. b 3.d 15. b 27. d 4. a 16. c 28. d 5. d 17. b 6. b 18. c 7.b 19. c MED 411 .CO MPRE M ED4 1. c 13. d 25. d 11. COM a. b. c. d. - PR EM ED4 11. COM - PR EM 28. I. Which has a lower characteristic stretching frequency, a C– H or C– D bond? II. How could IR distinguish between triethylamine, (CH3CH2)3 N, and methylethylamine, (CH3)(CH3CH2)NH? PRE D. Heller 5 8. c 20.e 9. d 21. b 10. b 22. d 11. d 23. d 12. d 24. b ...
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