Chapter 14 Homework Answers PDF

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Chapter 14 Homework Answers...

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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. "MALDI"?

In mass spectrometry, which of the following phrases is shortened to the acronym

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.

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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

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7. 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. 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. 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?

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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

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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. 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/e?

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.

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a. M − 29 b. M − 18 c. M − 15 d. M − 12 ANS: D

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20.

a. i b. ii c. iii d. iv ANS: A 21. a. hexane b. 1-chloropentane c. 1-pentanol d. 3-methylpentane ANS: C 22. a. hexane b. 1-chloropentane c. 1-pentanol d. 3-methylpentane ANS: D 23. a. 1-octyne b. 4-octyne c. 5-methyl-3-octyne d. 2,2-dimethyl-3-heptyne ANS: A 24. spectrum?

Which of the following does not give rise to a prominent M − 41 peak in the mass

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a. 1-hexene b. 3-methyl-1-hexene c. 4-methyl-1-hexene d. 5-methyl-1-hexene ANS: B 25. a. M − 15 b. M − 18 c. M − 21 d. M − 29 ANS: B

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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. a. cyclohexane b. cyclohexene c. 1-chlorocyclohexane d. cyclohexanol ANS: D 28. a. cyclopentane b. cyclopentene c. cyclopentanol d. methylcyclopentane ANS: D 29. a. 1-hexene b. 2-hexyne c. 3-hexanol d. 2-chlorohexane ANS: A 30. a. 1-hexanol b. 2-hexanol c. hexanal d. hexanoic acid ANS: C

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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

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33. of M − 31?

Which of the following gives rise to a prominent peak in the mass spectrum with m/z

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 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 moleuclar 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.

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ANS: C4H9Br 4. What is the most likely moleuclar 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

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5.

ANS: 85: loss of CH3• (15) by α-cleavage 72: loss of CH2=CH2 (28) by McLaferty rearrangement 43: loss of C4H9• (57) by α-cleavage 6.

ANS: 88: loss of CH2=CH2 (28) by McLaferty rearrangement 85: loss of CH3O• (31) by α-cleavage 59: loss of C4H9• (57) by α-cleavage 7.

ANS: 2-pentanol 8.

ANS: 2-methyl-2-butanol

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9.

ANS: 4-methyl-2-pentanone

10.

ANS: 2-methylpentanal

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