Question 1

Which of the following best describes the function of the magnet in a mass spectrometer?

Accepted Answer

It separates cations based on their mass-to-charge ratio ($$\frac{m}{z}).$$

Question 2

A molecule is ionized in a mass spectrometer to form a radical cation. Which equation correctly represents this process?

Accepted Answer

$$\mathrm{M} + e^- \rightarrow \mathrm{M}^{+\cdot} + e^-$$

Question 3

In the mass spectrum of methane ($$\mathrm{CH}_4$$), the base peak occurs at $$m/z = 16. $$What does this peak represent?

Accepted Answer

The molecular ion ($$\mathrm{CH}_4$$^{+\cdot}$$), representing the molecular weight.

Question 4

A mass spectrum of hexane ($$\mathrm{C}_6\mathrm{H}_{14}) $$shows a base peak at $$m/z = 57. $$Which fragment does this correspond to?

Accepted Answer

$$\mathrm{C}_4\mathrm{H}_9^+$$

Question 5

According to the nitrogen rule, which statement is correct?

Accepted Answer

A molecular ion with an odd mass always contains an odd number of nitrogen atoms.

Question 6

A compound containing chlorine shows two molecular ion peaks in its mass spectrum at $$m/z = 78$$ and $$m/z = 80$$ with a height ratio of 3:1. What does this indicate?

Accepted Answer

The compound contains one chlorine atom, due to $$^{35}\mathrm{Cl}$$ and $$^{37}\mathrm{Cl}$$ isotopes.

Question 7

Which fragmentation pattern is characteristic of aldehydes and ketones in mass spectrometry?

Accepted Answer

Alpha cleavage, breaking the bond between the carbonyl carbon and an adjacent carbon.

Question 8

Which equation represents the alpha cleavage of benzophenone in mass spectrometry?

Accepted Answer

$$\mathrm{C}_6\mathrm{H}_5COC_6\mathrm{H}_5$$^{+\cdot}$$ \rightarrow \mathrm{C}_6\mathrm{H}_5CO^+ + \mathrm{C}_6\mathrm{H}_5\cdot$$

Question 9

Which fragmentation pattern is commonly observed for alcohols in mass spectrometry?

Accepted Answer

Alpha cleavage between an alkyl group and the carbon bearing the OH group.

Question 10

A mass spectrum of triethylamine shows a peak at $$m/z = 101$$ and a fragment at $$m/z = 86. $$What fragmentation process is responsible for the $$m/z = 86$$ peak?

Accepted Answer

Alpha cleavage forming a resonance-stabilized carbocation.

Question 11

Which of the following is a major advantage of high-resolution mass spectrometry over low-resolution mass spectrometry?

Accepted Answer

It can measure the exact mass of isotopes to four decimal places, allowing for unambiguous determination of molecular formulas.

Question 12

A compound has a molecular ion at $$m/z = 60. $$Which formula would be ruled out by high-resolution mass spectrometry if the exact mass measured is $$60.0211$$?

Accepted Answer

$$\mathrm{C}_2\mathrm{H}_8\mathrm{N}_2$$

Question 13

In gas chromatography-mass spectrometry (GC-MS), what does the retention time indicate?

Accepted Answer

The time required for a compound to travel through the GC column.

Question 14

A urine sample is analyzed for THC using GC-MS. The mass spectrum shows a molecular ion at $$m/z = 314. $$What does this value represent?

Accepted Answer

The molecular weight of THC ($$\mathrm{C}_{21}\mathrm{H}_{30}\mathrm{O}_2).$$

Question 15

Which isotope pattern would you expect for a compound containing bromine in its mass spectrum?

Accepted Answer

Two molecular ion peaks with a height ratio of 1:1.

Question 16

When proposing possible molecular formulas for a compound with a molecular ion at $$m/z = 154$$, which step is used to determine the maximum number of carbons possible for a hydrocarbon?

Accepted Answer

Divide 154 by 12, the mass of $$^{12}\mathrm{C}$$, and the remainder gives the number of hydrogens.

Question 17

Which of the following best describes the base peak in a mass spectrum?

Accepted Answer

The peak with the highest relative abundance, often a fragment ion.

Question 18

Which real-world application is best suited for GC-MS analysis?

Accepted Answer

Analyzing mixtures of organic compounds, such as detecting drugs in urine.

Mass Spectrometry in Organic Chemistry: Principles, Interpretation, and Applications

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