Deck 13: Mass Spectrometry and Infrared Spectroscopy

Question 1

In an IR spectrum, which of the indicated C-H bonds exhibits a stretching absorption at the largest wave number?

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

Answer 1

I

Question 2

Why is the infrared absorption for the stretching motion of internal alkynes rarely observed?

A) They do not form cations.
B) They are too strong.
C) Stretching in internal alkynes does not involve a change in dipole moment.
D) They do not have hydrogens.

Answer 2

Stretching in internal alkynes does not involve a change in dipole moment.

Question 3

Which of the following statements is (are) accurate about the IR spectrum of compounds I, II, and III below?

A) Compound I shows absorptions at 2950 and 1700 cm^-1.
B) Compound II shows absorptions at 3200-3600 and 1650 cm^-1.
C) Compound III shows absorptions at 3200-3600 and 2950 cm^-1.
D) Both (Compound I shows absorptions at 2950 and 1700 cm^-1) and (Compound II shows absorptions at 3200-3600 and 1650 cm^-1) are true.

Answer 3

Both (Compound I shows absorptions at 2950 and 1700 cm^-1) and (Compound II shows absorptions at 3200-3600 and 1650 cm^-1) are true.

Question 4

Which of the following statements is (are) true about the IR spectrum of the compound drawn below?

A) It shows absorptions at 3000-3150 cm^-1 and 1720 cm^-1.
B) It shows absorptions at 3000-2850 cm^-1 and 2150 cm^-1.
C) It shows absorptions at 2250 cm^-1 and 1650 cm^-1.
D) It shows absorptions at 2250 cm^-1 and 1720 cm^-1.
E) Both statements B (It shows absorptions at 3000-2850 cm^-1 and 2250 cm^-1) and D (It shows absorptions at 2250 cm^-1 and 1720 cm^-1) are true.

Question 5

In electron impact mass spectrometry (EIMS), what is being detected?

A) The molecular mass of the compound
B) The molecular formula of the compound
C) The mass to charge ratio of any ionic species
D) The mass to charge ratio of any neutral species

Question 6

You are given a bottle of an organic liquid and told it must be either cyclohexane or 1-hexene. Which of the following statements is (are) true about these two compounds?

A) The two compounds can be differentiated by their mass spectra because they will have molecular ion peaks at different m/z.
B) 1-Hexene will show an absorption at 1650 cm^-1 but cyclohexane will not.
C) Both cyclohexane and 1-hexene will show C-H absorptions at about 2950 cm^-1.
D) Statements B (1-Hexene will show an absorption at 1650 cm^-1 but cyclohexane will not) and C (Both cyclohexane and 1-hexene will show C-H absorptions at about 2950 cm^-1) are both true.
E) Statements A (The two compounds can be differentiated by their mass spectra because they will have molecular ions at different masses), B (1-Hexene will show an absorption at 1650 cm^-1 but cyclohexane will not), and (Both cyclohexane and 1- hexene will show C-H absorptions at about 2950 cm^-1) are all true.

Question 7

You observe a compound that exhibits a mass spectrum with peak at 160 and a peak at 162, both of equal intensity. This compound contains:

A) Two chlorine atoms
B) One iodine atom
C) One bromine atom
D) Two bromine atoms

Question 8

What type of feature will be observed in the EI mass spectrum of chlorobenzene?

A) An absorption at 3100 cm^-1
B) A signal at 113.
C) A signal at 112 and a signal at 114 in a ratio of 3:1
D) A signal at 112 and a signal at 114 in a ratio of 1:1

Question 9

Which of the following statements is (are) true about a compound that has a molecular ion peak in its mass spectrum at mass 94, and shows prominent peaks in its IR spectrum at 3600-3200 and 1600 cm^-1?

A) The compound has a molecular mass of 94.
B) The compound contains a C=O group and C_sp3-H hybridized bonds.
C) The compound contains an OH group and a benzene ring.
D) Both A (The compound has a molecular mass of 94) and B (The compound contains a C=O group and C_sp3-H hybridized bonds) are true statements.
E) Both A (The compound has a molecular mass of 94) and C (The compound contains an OH group and a benzene ring) are true statements.

Question 10

Consider the three organic compounds drawn below. Which of the following statements is (are) true about the IR spectra of I, II, and III?

A) I shows strong absorptions at 2950 cm^-1 and 1700 cm^-1.
B) II shows strong absorptions at 2950 cm^-1 and 2250 cm^-1.
C) III shows strong absorptions at 2950 cm^-1 and 3200-3600 cm^-1.
D) Statements (I shows strong absorptions at 2950 cm^-1 and 1700 cm^-1) and (III shows strong absorptions at 2950 cm^-1 and 3200-3600 cm^-1) are true.

Question 11

Which of the indicated C-H bonds absorbs at the lowest wave number in the IR spectrum?

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

Question 12

Which of the following statements is (are) true about a compound that has a molecular ion peak in its mass spectrum at mass 104, and shows prominent peaks in its IR spectrum at 3200-2850 cm^-1?

A) The compound has a molecular mass of 104.
B) The compound contains a C=O group and C_sp3-H hybridized bonds.
C) The compound contains an OH group and C_sp3-H hybridized bonds.
D) Both (The compound has a molecular mass of 104) and (The compound contains a C=O group and C_sp3-H hybridized bonds) are true statements.
E) Both (The compound has a molecular mass of 104) and (The compound contains an OH group and C_sp3-H hybridized bonds) are true statements.

Question 13

A compound X has a molecular ion peak in its mass spectrum at m/z 136. What information does this tell us about X?

A) X has a molecular mass of 136.
B) The molecular formula for X is C₈H₈O₂.
C) The empirical formula for X is C₄H₄O.
D) Both A (X has a molecular mass of 136) and B (The molecular formula for X is C₈H₈O₂) are true.
E) Statements (X has a molecular mass of 136), (The molecular formula for X is C₈H₈O₂), and (The empirical formula for X is C₄H₄O) are all true.

Question 14

What type(s) of molecular motion is (are) observed using infrared spectroscopy?

A) Stretching and bending
B) Rotation and excitation
C) Spin flipping
D) Fragmentation

Question 15

Stronger bonds will be found where in the infrared spectrum?

A) Higher molecular weight
B) Lower molecular weight
C) Lower wavenumbers
D) Higher wavenumbers

Question 16

A compound X shows a molecular ion peak at m/z 72 in its mass spectrum, and a strong peak at ~1715 cm^-1 in its IR spectrum. Which structures are possible for compound X?

A) I
B) II
C) III
D) I and II

Question 17

The functional group region of an infrared spectrum is:

A) Where the cations appear
B) Greater than or equal to 1500 cm^-1
C) Less than 1500 cm^-1
D) Greater than or equal to 2500 cm^-1

Question 18

An alkyne C-H bond absorbs at higher wave number than an alkene C-H bond. What does this tell you about the strength of these two bonds?

A) The alkene C-H bond is stronger.
B) The alkyne C-H bond is stronger.
C) The alkene C-C bond is stronger.
D) The alkyne C-C bond is stronger.

Question 19

Why does an alkyne carbon-carbon triple bond vibrate at a higher wavenumber than an alkene carbon-carbon double bond?

A) It is stronger.
B) It is weaker.
C) It has fewer hydrogens.
D) It makes a less stable cation.

Question 20

Compared to a C-H bond, a C-D bond will vibrate where in the infrared spectrum?

A) Higher molecular weight
B) Lower molecular weight
C) Lower wavenumbers
D) Higher wavenumbers

Question 21

Examine the IR below and classify the compound.

A) Alcohol
B) Aldehyde
C) Carboxylic acid
D) Ketone

Question 22

Which of the following statement(s) is (are) true about a compound that has a molecular ion peak in its mass spectrum at mass 69, and shows a prominent peak in its IR spectrum at 2250 cm^-1?

A) The compound has a molecular mass of 70.
B) The compound contains a C=O group.
C) The compound contains a cyano or alkyne group.
D) Both (The compound has a molecular mass of 70) and (The compound contains a C=O group) are true statements.
E) Both (The compound has a molecular mass of 70) and (The compound contains a cyano or alkyne group) are true statements.

Question 23

The base peak in a mass spectrum corresponds to the most stable fragment. Propose a structure for a compound that is consistent with the following data.
(a) The molecular ion peak has m/z = 116
(b) The base peak is at m/z = 59.
(c) The compound is composed of C, H and O atoms.
(d) The IR spectrum shows a strong absorbance at 3257 cm^-1.

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

Question 24

Examine the IR below and classify the compound.

A) Alcohol
B) Arene
C) Amine
D) Ketone
E) Carbocylic acid

Question 25

What type of signal(s) would you observe in the mass and (or) infrared spectrum of the following compound?

A) A signal at 1600 cm^-1
B) A signal at 3300 cm^-1
C) A single mass peak at 92 amu
D) Two mass peaks at 92 and 94 amu

Question 26

Examine the IR below and classify the compound.

A) Alcohol
B) Aldehyde
C) Amine
D) Ketone

Question 27

When the phenol shown below is treated with KOH, it forms a product whose IR spectrum does not show an absorption in the 3200-3600 cm^-1 region. Propose a structure for the product.

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

Question 28

In a typical mass spectrum, a smaller signal is observed at a mass 1 amu higher than the molecular ion peak. Why?

A) Due to small impurities in the sample
B) Machine error
C) Because a small percentage of the compound will have a carbon that is the isotope ¹³C instead of ¹²C
D) Because of fragmentation

Question 29

Which of the following information is primarily obtained from an IR spectrum?

A) Conjugated $\pi$ system present in a compound.
B) Functional groups present in a compound.
C) Molecular weight of a compound.
D) The carbon and hydrogen framework of a compound.

Question 30

An IR spectrum has the following potentially important absorptions: 3091, 3067, 2963, 2921, 2252, 1603, 1499, 1455, 1416, 1078, 1031, 941, 735, and 696 cm^-1. Indicate which structure corresponds to the IR data.

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

Question 31

Which of the following compounds will have the lowest wavenumber for carbonyl absorption?

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

Question 32

Examine the IR below and classify the compound.

A) Alcohol
B) Aldehyde
C) Amine
D) Ketone
E) Carboxylic acid

Question 33

What type of signal(s) would you observe in the mass and/or infrared spectrum of the following compound?

A) A signal at 96 amu
B) Two signals at 112 and 114 amu
C) A signal at 1600 cm^-1
D) A signal at 1720 cm^-1

Question 34

Which of the following structures is consistent with a compound that displays a molecular ion peak at 103 and infrared signals at 2250 and 1600 cm^-1?

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

Question 35

Which of the following statements is (are) true about a compound that has molecular ion peaks in its mass spectrum at mass 170 and 172, and shows prominent peaks in its IR spectrum at 3150-3000 and 1600 cm^-1?

A) The compound is not pure.
B) The compound contains a halogen.
C) The compound contains an OH group and C_sp3-H hybridized bonds.
D) Both A (The compound is not pure) and B (The compound contains a halogen) are true statements.
E) Both A (The compound is not pure) and C (The compound contains an OH group and C_sp3-H hybridized bonds) are true statements.

Question 36

¹³C NMR is a technique in which the total number of signals represents the number of unique carbon atoms in a molecule. Propose a structure that is consistent with the following data.
(a) The IR includes peaks at 1603 and 1495 cm^-1.
(b) The ¹³C NMR has a total of 7 signals.
(c) The compound has one acidic proton.

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

Question 37

Which of the following structures is consistent with a compound that displays a molecular ion peak at 56 and infrared signals at 2250 and 3600-3200 cm^-1?

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

Question 38

Which of the following structures is consistent with a compound that displays a molecular ion peak at 84 and infrared signals at 3000-2850 cm^-1 and no signals between 3000-3300 cm^-1?

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

Question 39

What type of signal(s) would you observe in the mass and (or) infrared spectrum of the following compound?

A) A signal at 95 amu
B) A signal at 94 amu
C) Two signals at 95 and 94 amu
D) A signal at 3600-3200 cm^-1

Question 40

Examine the IR below and classify the compound.

A) Alkane
B) Carboxylic acid
C) Alcohol
D) Alkene

Question 41

Which of the following $\pi$ bonds is IR inactive?

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

Question 42

Which of the following statements about the base peak of a mass spectrum is always true?

A) The base peak corresponds to the molecular ion.
B) The base peak corresponds to the most abundant ion.
C) The base peak corresponds to the lowest m/z.
D) None of the above.