Question 1

Which of the following statements about the molecular ion (M*) in mass spectrometry is CORRECT?

Accepted Answer

The molecular ion is a radical cation formed by loss of an electron, and its mass equals the sum of the atomic masses of the most abundant isotopes.

Question 2

In the mass spectrum of methane ($$\mathrm{CH_4$}$$), the base peak is observed at $$m/z = 16. $$What does this peak represent?

Accepted Answer

The molecular ion ($$\mathrm{CH_4$^+}) $$containing the most abundant isotopes.

Question 3

Which of the following elements commonly found in organic compounds produces a characteristic M+2 peak in mass spectrometry due to its isotopic abundance?

Accepted Answer

Chlorine

Question 4

A mass spectrometer sorts ions by their mass-to-charge ratio ($$m/z). If an $$ion has a mass of 44 amu and a charge of +2, what is its $$m/z$$ value?

Accepted Answer

$$m/z = 22$$

Question 5

Which type of fragmentation is most characteristic for alcohols in mass spectrometry?

Accepted Answer

Alpha-cleavage and dehydration

Question 6

In infrared (IR) spectroscopy, which equation correctly relates the energy of a photon to its frequency?

Accepted Answer

$$E = h 
u$$

Question 7

Which functional group is most likely to show a strong absorption near $$1700\ \mathrm{cm}^{-1} in an IR $$spectrum?

Accepted Answer

Carbonyl ($$\mathrm{C=O}$$ stretch)

Question 8

Which statement best explains why the IR absorption for a $$\mathrm{C=O}$$ bond is typically more intense than that for a $$\mathrm{C=C}$$ bond?

Accepted Answer

The $$\mathrm{C=O}$$ bond has a larger dipole moment change during vibration.

Question 9

According to Hooke’s law, the frequency of a bond vibration in IR spectroscopy depends on which factors?

Accepted Answer

Force constant and reduced mass

Question 10

Which of the following is TRUE regarding the base peak in a mass spectrum?

Accepted Answer

It is the tallest peak and represents the most abundant ion.

Question 11

A compound shows a strong IR absorption at $$3300\ \mathrm{cm}^{-1}$$ and a broad peak. Which functional group is most likely present?

Accepted Answer

Alcohol ($$\mathrm{O-H}$$ stretch)

Question 12

Which of the following statements about fragmentation patterns in mass spectrometry is CORRECT?

Accepted Answer

Fragmentation patterns are unique and can be used as a molecular fingerprint.

Question 13

In mass spectrometry, why is the $$m/z$$ value typically equal to the mass of the ion?

Accepted Answer

Because the charge $$z is $$almost always +1.

Question 14

Which of the following is a common fragmentation pathway for ketones in mass spectrometry?

Accepted Answer

Alpha-cleavage adjacent to the carbonyl group

Question 15

A mass spectrum of an unknown compound shows a molecular ion peak at $$m/z = 44$$ and a significant M+2 peak. Which element is most likely present?

Accepted Answer

Sulfur

Question 16

Which region of the IR spectrum is most useful for identifying functional groups?

Accepted Answer

4000–2500 $$\mathrm{cm}^{-1}$$

Question 17

Which of the following best describes the process of ionization in mass spectrometry?

Accepted Answer

A molecule loses an electron to form a radical cation.

Question 18

Why does the IR absorption frequency increase as the bond strength increases?

Accepted Answer

Stronger bonds have higher force constants, leading to higher vibrational frequencies.

Question 19

Which of the following is TRUE regarding the analysis of isotopes in mass spectrometry?

Accepted Answer

Mass spectrometry analyzes the masses of individual isotopes, not the average.

Spectroscopy A & B: Mass Spectrometry and Infrared Spectroscopy

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