Question 1

Which of the following best describes the primary information obtained from mass spectrometry (MS) in organic chemistry?

Accepted Answer

The molecular mass and structural features of a compound

Question 2

In a mass spectrometer, what is the main purpose of the magnetic sector?

Accepted Answer

To separate charged fragments according to their $$m/z$$ values

Question 3

A compound with a molecular ion peak at $$m/z = 86 is $$analyzed. Which of the following molecular formulas is most consistent with a precise mass of $$86.1096$$ amu?

Accepted Answer

$$\mathrm{C_6H_{14}}$$

Question 4

Which of the following statements about the base peak in a mass spectrum is correct?

Accepted Answer

It is the peak with the greatest intensity, assigned as 100% abundance.

Question 5

A mass spectrum of a compound shows a molecular ion peak (M) and a significant M+2 peak of equal intensity. Which element is most likely present in the compound?

Accepted Answer

Bromine

Question 6

Which of the following best explains why the $$m/z = 15$$ peak is more intense in the mass spectrum of 2-methylbutane compared to pentane?

Accepted Answer

2-methylbutane has more methyl groups, leading to more stable $$\mathrm{CH_3$^+}$$ fragments.

Question 7

Which of the following is a correct representation of the electron-impact ionization process in mass spectrometry?

Accepted Answer

$$\mathrm{M} + e^- \rightarrow \mathrm{M}^+ + 2e^-$$

Question 8

A mass spectrum of an unknown compound shows a molecular ion peak at $$m/z = 78$$ and a strong fragment at $$m/z = 77. $$Which of the following is the most likely explanation for the $$m/z = 77$$ peak?

Accepted Answer

Loss of a hydrogen atom from the molecular ion

Question 9

Which isotope pattern in a mass spectrum would indicate the presence of chlorine in a compound?

Accepted Answer

A molecular ion (M) and M+2 peak in a 3:1 ratio

Question 10

Which of the following best describes the fragmentation pattern of an ether in mass spectrometry?

Accepted Answer

Cleavage occurs at the C–O bond, often producing alkoxy and carbocation fragments.

Question 11

A mass spectrum of 2-chloropropane shows a molecular ion peak at $$m/z = 78$$ and a significant M+2 peak at $$m/z = 80. $$What is the expected intensity ratio of these two peaks?

Accepted Answer

3:1

Question 12

Which of the following is a common diagnostic fragment observed in the mass spectrum of alkylbenzenes?

Accepted Answer

A strong peak at $$m/z = 91$$ due to the tropylium ion

Question 13

Which of the following best explains why the molecular ion peak is sometimes weak or absent in the mass spectrum of alcohols?

Accepted Answer

Alcohols often undergo rapid fragmentation after ionization, leading to a weak or absent molecular ion peak.

Question 14

Which of the following is a typical fragmentation pattern for ketones in mass spectrometry?

Accepted Answer

Alpha-cleavage resulting in the loss of an alkyl group adjacent to the carbonyl

Question 15

A compound with the formula $$\mathrm{C_2H_5Br} is $$analyzed by mass spectrometry. What is the expected ratio of the molecular ion peak (M) to the M+2 peak?

Accepted Answer

1:1

Question 16

Which of the following best describes the McLafferty rearrangement observed in the mass spectra of certain ketones?

Accepted Answer

A hydrogen atom is transferred from the gamma carbon to the carbonyl oxygen, resulting in cleavage and formation of an alkene.

Question 17

Which of the following is NOT a function of a mass spectrometer?

Accepted Answer

Determining the types of functional groups by IR absorption

Question 18

A mass spectrum of an unknown compound shows a series of peaks at $$m/z$$ values differing by 14 units (e.g., M, M-14, M-28, M-42). What does this pattern most likely indicate?

Accepted Answer

The presence of a straight-chain alkyl group

Question 19

Which of the following best explains why isotopic patterns are useful in mass spectrometry for identifying elements such as chlorine and bromine?

Accepted Answer

Chlorine and bromine have two major isotopes with significant natural abundances, leading to characteristic M and M+2 peak ratios.

Spectroscopy and Mass Spectrometry in Organic Chemistry

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