e. V Chemistry 262 Winter 2018 Exam 3

Transcription

1 Chemistry 262 Winter 2018 Exam 3 The following 90 point exam contains 22 questions, valued at 4 points/question. There are also 3 unknown analysis problems, valued at 10 points/question, of which you are to select 2 1 Name: 1. The IR spectrum of which of the following compounds is likely to show a small, sharp peak at 2200 cm -1? N H I II III a. I b. II c. III d. IV e. V IV V 1 4 x 22 = 88 points, 88 points + 20 points = 108 points 108 points 90 points = 18 points of potential extra credit? Inconceivable!

2 2. Excluding C-H absorptions, what significant changes would be expected for the following transformation when examined by IR spectroscopy? a. CH 3 MgBr b. H 3 + a. A peak around 1710 cm -1 would disappear and a new peak around cm -1 would appear b. A peak around 1710 cm -1 would appear and a peak around 1650 cm -1 would disappear c. A peak around 2150 cm -1 would disappear and a new peak around cm -1 would appear d. No significant changes would occur e. nly a change in intensity would occur 3. Excluding C-H absorptions, what significant changes would be expected for the following transformation when examined by IR spectroscopy? a. NaH b. CH 3 I CH 3 a. A peak around 3300 cm -1 would disappear b. A peak around 1710 cm -1 would appear and a peak around 3300 cm -1 would disappear c. A peak around 2150 cm -1 would disappear and a new peak around 3300 cm -1 would appear d. No significant changes would occur e. nly a change in intensity would occur

3 4. For the following compound, how many different signals would be observed in a proton NMR (presuming all were well resolved)? a. 4 b. 5 c. 6 d. 7 e For the following compound, how many different signals would be observed in a proton NMR (presuming all were well resolved)? a. 4 b. 5 c. 6 d. 7 e Which of the following compounds would not be represented by a singlet only in a 1 H-NMR spectrum? a. Neopentane b. Hexamethylbenzene c. Isobutane d. (Z)-1,2-dichloroethene e. (E)-1,2-dichloroethene

4 7. Consider the expected 1 H NMR spectrum of 1,1,3,3- tetramethylcyclopentane. Which of the following is likely to be observed? a. 7 signals: all singlets b. 7 signals: 4 singlets, 3 doublets c. 3 signals: all singlets d. 3 signals: 1 singlet, 2 doublets e. 3 signals: 2 singlets, 2 doublet 8. Which of the following best represents the predicted approximate chemical shift and coupling for the hydrogen(s) indicated by the arrow? CH 3 a. 1.1 ppm, singlet b. 2.1, triplet c. 3.4, triplet d. 4.5 ppm, singlet e. 5.3 ppm, doublet 9. Which of the following best represents the approximate predicted chemical shift and coupling for the hydrogens indicated with the arrow? N a ppm, singlet b ppm, doublet c ppm, triplet d ppm, triplet e ppm, doublet

5 10. Which of the following best represents the approximate predicted chemical shift and coupling for the hydrogens indicated with the arrow? a ppm, quartet b ppm, quartet c ppm, quartet d ppm, triplet e ppm, triplet 11. For the C2 methylene group in 1-bromopropane, what is the theoretical multiplicity in the proton NMR spectrum (presuming J AB is sufficiently different from J BC and the instrument possesses enough resolving power for the difference)? CH 3 CH 2 CH 2 Br a. 2 b. 5 c. 6 d. 8 e. 12 c b a 12. Consider the expected splitting of the C2 proton signal in the 1 H-NMR spectrum of 2-ethyl-1,3-propanediol. Presuming that the coupling constants for neighboring protons are sufficiently different, and that the instrument has sufficient resolving power, what is the theoretical multiplicity of the C2 proton signal? a. 6 b. 7 c. 12 d. 15 e. 27

6 13. A compound with the molecular formula C 4 H 10 gives a 1 H NMR spectrum consisting only of a quartet centered at 3.5 and a triplet at 1.1. The most likely structure for the compound is a. CH 3 CH 3 C b. CH 3 CH 3 c. d. e. CH 3 CH CH 3 CH 2 CH 2 CH 2 CH 3 CH 2 CH 2 CH 3 CH 3 CHCH 2 CH Which of the following compounds would not give rise to 4 signals in the proton NMR spectrum and 3 signals in the carbon NMR spectrum? I II III IV a. I b. II c. III d. IV e. All of the above fit the criteria

7 15. A bromodichlorobenzene which gives four signals in the broadband proton decoupled 13 C-NMR spectrum is consistent with: Br Br Br I Br II Br III a. I IV V b. II c. III d. IV e. V 16. What is the most likely structure of a compound of molecular formula C 9 H 12 that gives a proton NMR featuring (a) a doublet at 1.25 (b) a septet at 2.90 and (c) a multiplet at 7.25? I II III IV V a. I b. II c. III d. IV e. V

8 17. What is the structure of the compound of molecular formula C 9 H 10 2 that gives the following 1 H-NMR spectrum? Hint: the MS shows a neutral loss of 17 mass units from the molecular ion PPM a. CH b. C 2 H c. C 2 H d. e. H 2 C C 2 H

9 18. An unknown compound of molecular formula C 5 H 10 gives the following spectral data 1 H NMR spectrum IR spectrum doublet, 1.10 strong peak singlet, 2.10 near 1720 cm -1 septet, 2.50 Which of the following is the likely structure of the unknown? I II III a. I b. II c. III d. IV e. V IV V 19. Which of the following is the m/z for the molecular ion for the spectrum shown? a. 15 b. 29 c. 44 d. 45 e. 100

10 20. A prominent M peak is suggestive of what type of functional group? a. Alkane b. Alcohol c. Ether d. Ketone e. 1 o Amine 21. Predict the base peak for 2-chloro-2-methylpropane a. m/z = 15 b. m/z = 92 c. m/z 43 d. m/z = 57 e. m/z = The data below for the isotope envelope of the molecular ion region of a halogen containing species are consistent with the presence of what halogens for the compound in question? M +, I = 51.0 % M + + 2, I = % M + + 4, I = 49.0 % a. 1 Br b. 1 c. 1 Br, 1 d. 2 Br e. 2