Name: 1. Ignoring C-H absorptions, what characteristic IR absorption(s) would be expected for the functional group shown below?

Transcription

1 Chemistry 262 Winter 2018 Exam 3 Practice The following practice contains 20 questions. Thursday s 90 exam will also contain 20 similar questions, valued at 4 points/question. There will also be 2 unknown analysis problems valued at 10 points each, giving an opportunity for 10 extra credit points Name: 1. Ignoring C- absorptions, what characteristic IR absorption(s) would be expected for the functional group shown below? a. A peak around 1700 cm -1 b. A peak around 3300 cm -1 c. A peak around 1650 cm -1 d. A peak around 2250 cm -1 e. None of the absorbance values listed would indicate the functional group above 2. Ignoring C- absorptions, what characteristic IR absorption(s) would be expected for the functional group shown below? CN a. A peak around 1700 cm -1 b. A peak around 3300 cm -1 c. A peak around 1650 cm -1 d. A peak around 2250 cm -1 e. None of the absorbance values listed would indicate the functional group above

2 3. An optically active compound of molecular formula C 7 12, reacts with cold, dilute KMn 4 and gives a characteristic IR band around 3300 cm -1. n catalytic hydrogenation a new optically active compound is formed, with a formula C Which of the following compounds is a possible candidate? I II III IV V a. I b. II c. III d. IV e. V 4. IR evidence for the presence of an alkene would be most difficult for which of the following molecules? a. b. c. d. e.

3 5. Predict the splitting pattern you would observe for the proton at C1 of 2,3- dimethyl-2-phenylbutane a. Singlet b. Doublet c. Quartet d. Septet e. ctet 6. 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 best represents the approximate predicted chemical shift and coupling for the hydrogen indicated with the arrow? a. 1.1 ppm, singlet b. 2.1 ppm, doublet c. 3.4 ppm, singlet d. 3.5 ppm, quartet e. 4.5 ppm, singlet

4 8. Which of the following best represents the approximate predicted chemical shift and coupling for the hydrogen indicated with the arrow? a. 1.0 ppm, quartet b. 2.4 ppm, singlet c. 2.4 ppm, triplet d. 2.4 ppm, quartet e. 3.0 ppm, quartet 9. Which of the following best represents the approximate predicted chemical shift and coupling for the hydrogen indicated with the arrow? a. 5.4 ppm, doublet b. 1.0 ppm, multiplet c. 2.0 ppm, doublet d. 1.0 ppm, doublet e. 5.4 ppm, multiplet 10. Assuming all are resolved, how many different signals would be observed in the 1 -NMR of the following compound? a. 1 b. 2 c. 3 d. 4 e. 5

5 11. ow many signals would be observed in the 1 -NMR of trans-1,2- dichlorocyclopropane? a. 1 b. 2 c. 3 d. 4 e Which of the following compounds would consist of one triplet, one singlet, and one quartet? a. 2-chloro-4-methylpentane b. 3-chloro-2-methylpentane c. 3-chloropentane d. 1-chloro-2,2-dimethylbutane e. 3-chloro-3-methylpentane 13. An organic compound absorbs strongly in the IR at 1687 cm -1. The 1 -NMR for the compound consists of 2 signals a singlet at 2.1 ppm and a multiplet centered at 7.1 ppm. The MS shows significant peaks at m/z 120, 105, and 77. The above information is consistent with which of the following structures? I II III a. I b. II c. III d. IV e. V IV V

6 14. Which of the indicated protons has its 1 -NMR signal furthest downfield? Cl III I C C C II C IV V a. I b. II c. III d. IV e. V 15. Assuming all are resolved, how many different signals would be observed in the 13 C-NMR of the following compound? S S a. 4 b. 5 c. 6 d. 7 e Assuming all peaks are resolved, which of the following would give rise to 4 peaks in both the 1 -NMR and broadband decoupled 13 C-NMR spectra? Br I II III IV a. I b. II c. III d. IV e. More than one of the above

7 17. The broadband decoupled 13 C-NMR spectrum of a hexylchloride exhibits 5 signals. Which of the following consistent with this information? a. CC 2 C 2 Cl b. Cl C 2 CC 2 c. C C d. Cl CCC 2 e. Cl C C Cl

8 18. An unknown compound of formula C gives the following 1 -NMR spectrum. The broadband decouple 13 C-NMR spectrum shows a characteristic peak at 174 ppm. Which of the following structures is consistent with this information? PPM a. b. c. d. e.

9 19. Which of the following compounds of formula C 6 14 would give a MS base peak of m/z = 43? a. C 2 C 2 C 2 C 2 b. ( C 2 ) 2 C c. ( ) 3 CC 2 d. ( ) 2 CC( ) 2 e. None of these 20. 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 = % M + + 2, I = 64.0 % M + + 4, I = 10.0 % a. 1 Br b. 1 Cl c. 1 Br, 1 Cl d. 2 Br e. 2 Cl