Deck 14: Mass Spectrometry, Infrared Spectroscopy, and Uvvis Spectroscopy

Question 1

Give the m/z ratio that corresponds to the molecular ion in the mass spectrum of ethylpropylamine.

Answer 1

87

Question 2

Which of the following statements is true about a molecular ion?

A)It is a compound that lost a pair of electrons.
B)It is a compound that gained a pair of electrons.
C)It is a compound that gained one electron.
D)It is a compound that lost one electron.
E)It is a compound that carries a free radical and a negative charge.

Answer 2

It is a compound that lost one electron.

Question 3

Which of the following statements best explains how a hydrocarbon can show an M+2 peak in mass spectrometry?

A)from ¹³C and ¹H
B)from ¹²C and ²H
C)from a single ¹³C
D)from a single ³H
E)from two ¹³C's

Answer 3

from two ¹³C's

Question 4

Describe the fate of a molecule from introduction to detection in a mass spectrometer.

Question 5

Which of the following statements best explains the information we can gain from mass spectrometry?

A)It allows us to determine the number of protons in a compound.
B)It allows us to determine the kinds of functional groups in a compound.
C)It allows us to determine the molecular weight and the mass of some fragments of a compound.
D)It allows us to determine the presence and nature of a carbocation in the compound.
E)It allows us to determine the presence and nature of a free radical in the compound.

Question 6

What does "m/z" stand for and what does it mean?

Question 7

Which of the following is not a major peak in the MS of isopentane?

A)29
B)43
C)57
D)60
E)72

Question 8

Give the m/z ratio that corresponds to the molecular ion in the mass spectrum of 2-pentanone.

A)28
B)43
C)58
D)71
E)86

Question 9

What m/z value would you predict for the most stable fragment peak in the mass spectrum of 4-ethylheptane?

A)128
B)127
C)113
D)99
E)85

Question 10

Which of the following is not true about the M+1 peak?

A)It is one m/z unit higher than the base peak.
B)It is one m/z unit higher than the molecular ion peak.
C)It is one m/z unit higher than the parent ion peak.
D)It occurs because there is more than one naturally occurring isotope of carbon.
E)This means that the number of carbon atoms in a compound can be calculated if the relative abundance of both the M and M+1 peaks is known.

Question 11

Which of the following statements best describes the meaning of the following species: [CH₃CH₂CH₃] ∙ + ?

A)It is the molecular ion of propane.
B)It is the parent ion of propane.
C)It is the radical cation of propane.
D)The m/z value is 44.
E)all of the above

Question 12

Which of the following characterizes the unusually intense peak of alkyl chlorides in MS spectrometry?

A)M + 1 peak
B)M + 2 peak
C)base peak
D)parent peak
E)none of the above

Question 13

Which of the following molecular changes is necessary for mass spectrometry to occur?

A)excitation of an electron from the ground state to higher energy state
B)change of alignment of an electron in a magnetic field
C)change of alignment of a proton in a magnetic field
D)loss of an electron
E)molecular vibration

Question 14

Give the m/z ratio of the molecular ion in the mass spectrum of 1-butanol.

Question 15

Give the m/z ratio that corresponds to the molecular ion in the mass spectrum of 2-bromobutane.

Question 16

Which of the following m/z values is the molecular ion for 2-butanone?

A)15
B)29
C)43
D)57
E)72

Question 17

Which of the following is true about the base peak in mass spectrometry?

A)The m/z value equals the molecular weight of the compound.
B)The m/z value corresponds to a very stable carbanion.
C)It has the largest peak height in the spectrum.
D)It has the highest m/z value of all the peaks in the spectrum.
E)The base peak is assigned a relative abundance equal to that of the parent ion.

Question 18

2-Methylhexane shows an intense peak in the mass spectrum at m/z = 43. Propose a likely structure for this fragment.

Question 19

Predict the molecular formula of the compound represented below based on the MS data given.

A)C₆H₁₂
B)C₅H₂₄
C)C₄H₆O₂
D)C₃H₈O₂
E)C₅H₈O

Question 20

How could you distinguish the mass spectrum of 2,2-dimethylpropane from that of isopentane?

Question 21

Which of the following m/z values is the base peak for benzyl alcohol?

A)77
B)108
C)91
D)17
E)52

Question 22

The mass spectra of alcohols often fail to exhibit detectable M peaks but instead show relatively large ________ peaks.

A)M+1
B)M+2
C)M-16
D)M-17
E)M-18

Question 23

Provide the structure of the species which results when the molecular ion of 4-heptanone undergoes fragmentation via a McLafferty rearrangement.

Question 24

In the mass spectrum of bromoform, CHBr₃, molecular ion peaks appear at m/z 250, 251, 252, and 253? What is the ratio of the intensities of these peaks?

A)1:1:1:1
B)1:2:2:1
C)1:3:3:1
D)2:3:3:2
E)3:2:2:3

Question 25

Which of the following is the base peak for the compound below?

A)77
B)92
C)15
D)57
E)43

Question 26

Describe the molecular ion region in the mass spectrum of CH₃CH₂Br.

Question 27

Show the m/z values of the molecular ion and 5 likely fragments for the compound ethyl ether,
CH₃CH₂OCH₂CH₃

Question 28

Which of the following is/are true about the MS of 1-bromobutane?

A)Peaks of approximately equal intensity are observed at m/z 136 and 138.
B)The major fragmentation occurs by cleavage of the C-Br bond.
C)The most intense peak occurs at m/z 43.
D)both A and B
E)both B and C

Question 29

In the mass spectrum of 2-chloropropane, what is the m/z of the molecular ion peak of greatest intensity?

A)63
B)76
C)78
D)80
E)82

Question 30

Which compound's mass spectrum shows peaks at M, M+2, and M+4 whose abundances are in a ratio of 1:2:1?

A)cyclohexanol
B)chlorocyclohexane
C)1,2-dichlorocyclohexane
D)1-bromopentane
E)1,5-dibromopentane

Question 31

Provide the structure of the two ions which result when the molecular ion of 2-methoxypentane undergoes fragmentation by

Question 32

Which of the following structures will give a base peak of 43 in mass spectrometry?

A)
B)CH₃CH₂CH₂CH₂CH₂CH₃
C)
D)
E)none of the above

Question 33

In the mass spectrum of 1,2-dichloroethane, what is the m/z of the molecular ion peak of greatest intensity?

A)94
B)96
C)98
D)100
E)102

Question 34

Which of the following m/z values is least intense in the mass spectrum of 1-chloropropane?

A)80
B)79
C)78
D)65
E)63

Question 35

What technique can be used to determine the molecular formula of a compound?

Question 36

The mass spectrum of an unknown compound has a molecular ion peak with a relative abundance of 43.27% and an M + 1 peak with a relative abundance of 3.81%. How many carbon atoms are in the compound?

Question 37

A compound shows a molecular ion peak at m/z 167. The relative intensities of the M and M+1 peaks are 50.0 and 4.4 respectively. How many carbons are in each molecule of the compound?

Question 38

Which of the following compounds exhibits the pattern of m/z values shown below? 41, 43, 57, 87, 101, 116

A)propylbromide
B)isopropyl bromide
C)sec-butyl isopropyl ether
D)2-hexanol
E)2-butanone

Question 39

An acylium ion is often produced as a fragment in the MS of which of the following class of organic compounds?

A)ketones
B)ethers
C)alkyl halides
D)alcohols
E)peroxides

Question 40

Is it possible to have an M + 2 peak in mass spectrometry? Explain.

Question 41

Which m/z peak is expected to be the base peak of cyclopentanol?

A)57
B)43
C)29
D)85
E)86

Question 42

Give the fragment(s)that corresponds to a m/z charge of 58 for ethylpropylamine.

A)
B)
C)
D)
E)

Question 43

Ethyl acetate has the structure CH₃CO₂CH₂CH₃. Which set of m/z peaks is most consistent with this structure?

A)88, 73, 43
B)88, 76, 45
C)88, 73, 45
D)88, 76, 43
E)88, 72, 70, 44

Question 44

How many centimeters (cm)are there in one micrometer (μm)?

A)10^-6
B)10^-3
C)10^-5
D)10^-8
E)10^-4

Question 45

Which of the following is highest in energy per photon?

A)electromagnetic radiation with a wavenumber of 10^-2 cm^-1
B)electromagnetic radiation with a frequency of 10⁷ s^-1
C)electromagnetic radiation with a frequency of 10⁵ s^-1
D)electromagnetic radiation with a wavelength of 10 cm
E)electromagnetic radiation with a wavenumber of 10⁶ cm^-1

Question 46

Arrange the following regions of the electromagnetic spectrum in order of decreasing wavelength: microwaves, visible light, ultraviolet light, infrared radiation, X-rays.

Question 47

When cyclopentanol is treated with chromic acid, the alcohol is oxidized to cyclopentanone. Which m/z peak is expected to be the base peak of cyclopentanone?

A)55
B)43
C)29
D)84
E)85

Question 48

Give the ion that corresponds to a m/z ratio of 58 in a mass spectrum of 2-pentanone.

A)
B)
C)
D)
E)

Question 49

Which region of the electromagnetic spectrum, IR or X-ray, is characterized by waves of lower frequency?

Question 50

Give the ion that corresponds to a m/z ratio of 43 in a mass spectrum of 2-pentanone.

A)
B)
C)
D)
E)

Question 51

Give the ion that corresponds to a m/z ratio of 56 in a mass spectrum of 1-butanol.

A)
B)
C)
D)
E)none of the above

Question 52

Which has the higher speed in a vacuum, ultraviolet or infrared light?

Question 53

Which of the following statements is not true about electromagnetic radiation?

A)The velocity of light is directly proportional to the energy.
B)All molecules absorb electromagnetic radiation at some frequency.
C)Frequency is inversely proportional to wavelength.
D)Energy is directly proportional to frequency.
E)Energy is inversely proportional to wavelength.

Question 54

Which region of the electromagnetic spectrum, IR or UV, contains photons of the higher energy?

Question 55

Which of the following normally occurs in a molecule when a photon of infrared light is absorbed?

A)An electron moves to an orbital of higher potential energy.
B)A transition between allowed vibrational energy states occurs.
C)An electron changes alignment in a magnetic field.
D)The molecule gains an electron.
E)The molecule loses an electron.

Question 56

Give the ion that corresponds a m/z ratio of 31 in a mass spectrum of 1-butanol.

A)
B)
C)
D)
E)

Question 57

Which of the following regions of the electromagnetic spectrum has the greatest energy per photon?

A)visible
B)microwave
C)radio
D)ultraviolet
E)infrared

Question 58

An infrared wavelength of 4.48μm is equivalent to a wavenumber of ________ cm^-1.

Question 59

In the electromagnetic spectrum, ________ frequencies, ________ wavenumbers, and ________ wavelengths are associated with high energy.

A)high, small, long
B)low, large, short
C)low, small, short
D)high, large, short
E)high, small, short

Question 60

Which region of the electromagnetic spectrum, radio or visible, is characterized by waves of shorter wavelength?

Question 61

Does the position of the stretch of the oxygen-hydrogen bond in alcohols depend on the concentration of the alcohol?

Question 62

Identify the bond with the lowest wavenumber in the IR spectrum.

A)C=O
B)C-O
C)O-H in alcohol
D)N-H
E)C-H

Question 63

Which molecule below has a significant band in the 1720 - 1780 cm^-1 range of its IR spectrum?

A)CH₃CH₂CH₂OH
B)CH₃C≡CCH₂CH₃
C)CH₃CH₂CH(NH₂)CH₃
D)(CH₃)₃N
E)CH₃CO₂CH₂CH₃

Question 64

Identify the compound that has a formula of C₅H₁₀ and bending vibrations at 990 and 910 cm^-1.

A)1-pentene
B)cis-2-pentene
C)trans-2-pentene
D)2-methyl-1-butene
E)2-methyl-2-butene

Question 65

While cleaning the organic stockroom, a student found a bottle of ethanol labeled "Denatured with Benzene." He decided to determine the concentration of benzene in the ethanol by acquiring the UV spectrum of the liquid in a 2.0 cm cell. The spectrum exhibited an absorption band at 260 nm which was attributable to benzene, and the absorbance of this band was 0.69. In a reference source, the student found that the molar absorptivity of this benzene band in ethanol was 230 M^-1cm^-1. Show how the student calculated the concentration of the benzene in the ethanol.

Question 66

Which compound would be expected to show intense IR absorption at 1715 cm^-1?

A)CH₃CH₂CO₂H
B)1-hexene
C)2-methylhexane
D)CH₃CH₂CH₂NH₂

Question 67

Which compound's carbonyl stretch occurs at the lowest wavenumber?

A)CH₃CH₂CH₂CHO
B)CH₃COCH₂CH₃
C)CH₃CH₂CONH₂
D)CH₃CH₂CO₂CH₃
E)CH₃CH₂COCH₂CH₃

Question 68

At what wavenumber will the C-H stretch involving an sp carbon appear?

A)2700 cm^-1
B)2900 cm^-1
C)3100 cm^-1
D)3300 cm^-1
E)3500 cm^-1

Question 69

Which molecule below has a significant band in the IR at 2220 cm^-1 (medium)?

A)CH₃CH₂CH₂OH
B)CH₃C≡CCH₂CH₃
C)CH₃CH₂CH(NH₂)CH₃
D)(CH₃)₃N
E)CH₃CO₂CH₂CH₃

Question 70

Which of the following carbonyl groups exhibits the highest wavenumber in infrared spectroscopy?

A)I
B)II
C)III
D)IV
E)V

Question 71

Which compound would be expected to show intense IR absorption at 1746 cm^-1?

A)CH₃CH₂OCH₂CH₃
B)CH₃CO₂CH₃
C)CH₃CH₂CCH
D)CH₃CH₂SCH₃

Question 72

Which of the following wavenumbers corresponds to the bond shown below? C C

A)1650 cm^-1
B)2100 cm^-1
C)1100 cm^-1
D)3300 cm^-1
E)2850 cm^-1

Question 73

Which of the following are considered to be bending (in-plane)vibrations?

A)scissoring and wagging
B)scissoring and twisting
C)rocking and wagging
D)rocking and twisting
E)scissoring and rocking

Question 74

Which of the following solvents is best used in infrared spectroscopy?

A)I
B)II
C)III
D)IV
E)V

Question 75

Which of the infrared regions is considered to be the fingerprint region?

A)4000cm^-1 - 1000cm^-1
B)4000μm - 1000μm
C)2200μm - 1000μm
D)1000cm^-1 - 400cm^-1
E)1000μm - 400μm

Question 76

Which compound's carbonyl stretch occurs at the greatest wavenumber?

A)CH₃CH₂CH₂CHO
B)CH₃COCH₂CH₃
C)CH₃CH₂CONH₂
D)CH₃CH₂CO₂CH₃
E)CH₃CH₂COCH₂CH₃

Question 77

Which of the following increases the absorbance of a solution of phenol in ethanol?

A)increasing the amount of phenol in the solution
B)decreasing the amount of ethanol in the solution
C)decreasing the light path through the solution
D)both A and B
E)both B and C

Question 78

Which molecule below has a significant band in the IR at 3400 cm^-1 (strong and broad)?

A)CH₃CH₂CH₂OH
B)CH₃C≡CCH₂CH₃
C)CH₃CH₂CH(NH₂)CH₃
D)(CH₃)₃N
E)CH₃CO₂CH₂CH₃

Question 79

Which of the following statements best explains the information we can gain from infrared spectroscopy?

A)It allows us to determine the number of protons in a compound.
B)It allows us to determine the kinds of functional groups in a compound.
C)It allows us to determine the molecular weight and the mass of some fragments of a compound.
D)It allows us to determine the presence and nature of a carbocation in the compound.
E)It allows us to determine the presence and nature of a free radical in the compound.

Question 80

Which of the following is not a common bending vibration of a CH₂ group?

A)flip
B)rock
C)scissor
D)twist
E)wag