Organic chemistry, 7e Brown Chapter 14

CHAPTER 14—MASS SPECTROMETRY MULTIPLE CHOICE 1. What is the principle that allows us to use mass spectrometry to determine the molecular weight of a compound? a. higher molecular weight compounds are less volatile b. higher molecular weight compounds are more dense c. a beam of higher molecular weight cations is deflected less by a magnetic field d. ions with higher molecular weight absorb higher frequencies of light ANS: C 2. In mass spectrometry, which of the following phrases is shortened to the acronym "FAB"? a. flight averaged bumping b. fast atom bombardment c. fragmented atom beam d. flying atom bashing ANS: B 3. In mass spectrometry, which of the following phrases is shortened to the acronym "EI"? a. electron injection b. electron impact c. energy initiated d. energy insertion ANS: B 4. In mass spectrometry, which of the following phrases is shortened to the acronym "MALDI"? a. mass analysis by light-detected ions b. matrix assisted laser desorption ionization c. many atom loss-detecting ionization d. molecular and light detecting instrument ANS: B 5. What is the x-axis of a mass spectrum? a. mass b. mass/energy c. mass/charge d. charge ANS: C 6. What is the y-axis of a mass spectrum? a. mass b. energy c. abundance d. field strength ANS: C 7. Which of the following is the definition of the base peak of a mass spectrum? a. the peak corresponding to the most abundant ion b. the peak corresponding to the ion with lowest m/e c. the peak corresponding to the molecular ion peak d. the peak corresponding to the ion arising to loss of a proton from the molecular ion ANS: A 8. Which of the following corresponds to the molecular ion in EI mass spectrometry? a. the most abundant ion b. the ion with the smallest m/e c. the ion formed by removal of an electron from the molecule d. any ion formed by fragmentation of the molecule ANS: C 9. What are products of the collision between high energy electrons and methane? a. CH4??? + 2 e? b. CH3? + H? c. CH4+? + 2 e? d. CH3? + H+ + 2 e? ANS: C 10. Which of the following sets of molecular ions does an alkyl bromide possess? a. two molecular ions in a 2:1 ratio separated by two mass units b. two molecular ions in a 1:1 ratio separated by two mass units c. three molecular ions in a 1:2:1 ratio separated by two mass units d. two molecular ions in a 3:1 ratio separated by two mass units ANS: B 11. Which of the following sets of molecular ions does an alkyl chloride possess? a. two molecular ions in a 2:1 ratio separated by two mass units b. two molecular ions in a 1:1 ratio separated by two mass units c. three molecular ions in a 1:2:1 ratio separated by two mass units d. two molecular ions in a 3:1 ratio separated by two mass units ANS: D 12. Which of the following sets of molecular ions does a dibromoalkane possess? a. two molecular ions in a 2:1 ratio separated by two mass units b. two molecular ions in a 1:1 ratio separated by two mass units c. three molecular ions in a 1:2:1 ratio, separated by two mass units d. two molecular ions in a 3:1 ratio separated by two mass units ANS: C 13. Which of the following is most consistent with a molecule having a molecular ion with m/e of 77? a. the molecule contains bromine b. the molecule contains nitrogen c. the molecule is an alcohol d. the molecule is a hydrocarbon ANS: B 14. How many carbon atoms are present in a molecule which gives an M+1 peak that is 5.74% of the intensity of the molecular ion? a. 5 b. 6 c. 11 d. 12 ANS: A 15. How many carbon atoms are present in a molecule which gives an M+1 peak that is 11.48% of the intensity of the molecular ion? a. 5 b. 6 c. 11 d. 12 ANS: C 16. Which of the molecules gives rise to a molecular ion with an odd value of m/z? a. C6H12Cl2 b. C7H10N2 c. C8H13N d. C8H14Br2 ANS: C 17. Which of the molecules gives rise to a molecular ion with an odd value of m/z? a. C6H12O2 b. C7H10ClN c. C8H18N2 d. C8H12 ANS: B 18. What are the most common products of the fragmentation of a molecular ion? a. two radicals b. an anion and a cation c. a radical and a cation d. two cations ANS: C 19. Which of the following is not prominent in the mass spectrum of 2-methyl-2-butanol? a. M ? 29 b. M ? 18 c. M ? 15 d. M ? 12 ANS: D 20. Which of the following bonds of the octane radical cation is least subject to fragmentation? a. i b. ii c. iii d. iv ANS: A 21. Which of the following gives rise to a prominent M ? 18 peak in the mass spectrum? a. hexane b. 1-chloropentane c. 1-pentanol d. 3-methylpentane ANS: C 22. Which of the following gives rise to a prominent M ? 15 peak in the mass spectrum? a. hexane b. 1-chloropentane c. 1-pentanol d. 3-methylpentane ANS: D 23. Which of the following gives rise to a prominent peak in the mass spectrum at m/z of 39? a. 1-octyne b. 4-octyne c. 5-methyl-3-octyne d. 2,2-dimethyl-3-heptyne ANS: A 24. Which of the following does not give rise to a prominent M ? 41 peak in the mass spectrum? a. 1-hexene b. 3-methyl-1-hexene c. 4-methyl-1-hexene d. 5-methyl-1-hexene ANS: B 25. Which of the following is not prominent in the mass spectrum of 2-methyl-2-butanol? a. M ? 15 b. M ? 18 c. M ? 21 d. M ? 29 ANS: B 26. Which of the following alcohols does not give a prominent M ? 15 ion? a. isopropyl alcohol b. tert-butyl alcohol c. 2-hexanol d. 3-pentanol ANS: D 27. Which of the following gives rise to a prominent M ? 18 peak in the mass spectrum? a. cyclohexane b. cyclohexene c. 1-chlorocyclohexane d. cyclohexanol ANS: D 28. Which of the following gives rise to a prominent M ? 15 peak in the mass spectrum? a. cyclopentane b. cyclopentene c. cyclopentanol d. methylcyclopentane ANS: D 29. Which of the following gives rise to a prominent peak in the mass spectrum with m/z of 41? a. 1-hexene b. 2-hexyne c. 3-hexanol d. 2-chlorohexane ANS: A 30. Which of the following gives rise to a prominent peak in the mass spectrum with m/z of 43? a. 1-hexanol b. 2-hexanol c. hexanal d. hexanoic acid ANS: C 31. Which of the following gives rise to a prominent peak in the mass spectrum with m/z of 45? a. 1-hexanol b. 2-hexanol c. hexanal d. hexanoic acid ANS: D 32. Which of the following gives rise to a prominent peak in the mass spectrum with m/z of 60? a. 1-hexanol b. 2-hexanol c. hexanal d. hexanoic acid ANS: D 33. Which of the following gives rise to a prominent peak in the mass spectrum with m/z of M ? 31? a. 2-methylhexanoic acid b. methyl hexanoate c. ethyl hexanoate d. hexanoic acid ANS: B 34. Which of the following gives rise to a prominent peak in the mass spectrum with m/z of 91? a. 1-octene b. 1-hexanamine, CH3CH2CH2CH2CH2CH2NH2 c. benzene d. ethylbenzene ANS: D 35. Which of the following gives rise to a prominent peak in the mass spectrum with m/z of 30? a. 1-hexanamine, CH3CH2CH2CH2CH2CH2NH2 b. 1,1-dimethyl-1-butanamine, CH3CH2CH2C(CH3)2NH2 c. 1-hexanol d. hexanal ANS: A TRUE/FALSE 1. Both mass spectrometry and infrared spectroscopy involve the interaction of molecules with electromagnetic energy. ANS: F 2. C6H15N could have a mass spectrum with M+ at m/z = 101 with a minor M+1 peak. ANS: T 3. Loratidine is the active ingredient in the antihistamine Claritin®. Mass spectral analysis of loratidine shows M+ at m/z = 382 and M+ at m/z = 384 in an approximate ratio of 3:1 in intensity. This data indicates that loratidine contains fluorine. ANS: F 4. Alpha cleavage of the following compound would produce fragments at m/z = 43 and m/z = 119. ANS: T 5. It is not possible distinguish 2,2-dimethylbutane from 2-methylpentane using mass spectrometry. ANS: F 6. Mass spectrometry and infrared spectroscopy are complementary techniques because mass spectrometry provides information about the molar mass and formula while infrared spectroscopy helps identify the functional groups in the formula. ANS: T 7. Consider the following mass spectrum C5H12O might have been used to produce this spectrum. ANS: F 8. A monochloroalkane shows two parent ion peaks m/z at 92 and 94. The molecular formula of this compound might be C3H7Cl. ANS: F 9. The mass spectrum of 1-pentanol shows an intense daughter ion peak at m/z = 31. This peak could be due to the formation of CH3O+. ANS: T COMPLETION The following question(s) refer to the mass spectrum shown below. Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ 1. The base peak in this spectrum occurs at a m/z of ______. ANS: 77 2. This compound contains C, H, and one other atom. The other atom from the mass spectrum is __________. ANS: Br bromine Refer to the mass spectrum of 2-methylbutane shown below to answer the following question(s). Spectrum obtained from: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ 3. The peak at a m/z of _____ represents M+. ANS: 72 4. The peak at a m/z of _____ represents the base peak. ANS: 43 5. The peak at a m/z of _____ represents the following species. ANS: 57 6. The peak at a m/z of _____ represents the following species. ANS: 43 7. The peak at a m/z of _____ represents the following species. +CH2CH3 ANS: 29 8. The mass of the larger charged fragment produced by the dehydration of the following compound occurs at a m/z of _______. ANS: 126 9. Cyclohexene and hex-2-yne both have the molecular formula, C6H10. The mass spectrum below belongs to ___________________. ANS: cyclohexene 10. Alpha cleavage of the following compound will produce a peak at a m/z of _______. ANS: 31 11. Dehydration of the following compound will produce a peak at a m/z of _______. ANS: 82 PROBLEM 1. What is the most likely molecular formula of a compound that has a molecular ion in the EI mass spectrum with m/z of 97 and an M+1 peak that is 6.6% of the intensity of the molecular ion peak? ANS: C6H11N 2. What is the most likely molecular formula of a compound (that contains only C, H and O) which has a molecular ion in the EI mass spectrum with m/z of 104 and an M+1 peak that is 5.5% of the intensity of the molecular ion peak? ANS: C5H12O2 3. What is the most likely molecular formula of a compound that has a molecular ion in the EI mass spectrum with m/z of 136, with a M+1 and M+2 peaks that are 4.4% and 49% of the intensity of the molecular ion peak, respectively. ANS: C4H9Br 4. What is the most likely molecular formula of a compound that has a molecular ion in the EI mass spectrum with m/z of 120, with a M+1 and M+2 peaks that are 6.6% and 24% of the intensity of the molecular ion peak, respectively. ANS: C6H13Cl 5. Provide the mass of the three most prominent fragment peaks that are observed in the EI mass spectrum of 2-hexanone, CH3CH2CH2CH2COCH3 (molecular ion m/z = 100) and describe the processes that lead to each of these fragments. ANS: 85: loss of CH3• (15) by ?-cleavage; 72: loss of CH2=CH2 (28) by McLaferty rearrangement; 43: loss of C4H9• (57) by ?-cleavage 6. Provide the mass of the three most prominent fragment peaks that are observed in the EI mass spectrum of methyl pentanoate, CH3CH2CH2CH2CO2CH3 (molecular ion m/z = 116) and describe the processes that lead to each of these fragments. ANS: 88: loss of CH2=CH2 (28) by McLaferty rearrangement; 85: loss of CH3O• (31) by ?-cleavage; 59: loss of C4H9• (57) by ?-cleavage 7. Which C5H12O compound give the following EI mass spectrum? ANS: 2-pentanol 8. Which C5H12O compound give the following EI mass spectrum? ANS: 2-methyl-2-butanol 9. Which C6H12O carbonyl-containing compound shows a molecular ion peak at m/z 100 and significant fragment peaks at m/z 85, 58, 57, 43 and 42 in the EI mass spectrum? ANS: 4-methyl-2-pentanone 10. Which C6H12O carbonyl-containing compound shows a molecular ion peak at m/z 100 and significant fragment peaks at m/z 71, 58, 57, 43 and 29 in the EI mass spectrum? ANS: 2-methylpentanal