Mass spectroscopy

Relative abundance is the unit along the y-axis in a mass spectrum. What are the units on the x-axis?

mass/charge (m/z)

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

72

What are the most common products of the fragmentation of a molecular ion?

 

a radical and a cation

 

two cations

 

an anion and a cation

 

two radicals

A radical and cation

Which of the molecules gives rise to a molecular ion with an odd value of m/z?

C₇H₁₀ClN

Which of the following gives rise to a prominent peak in the mass spectrum with m/z of M − 31?

methyl hexanoate

Which of the following gives rise to a prominent M − 15 peak in the mass spectrum?

methylcyclopentane

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

It allows us to determine the molecular weight and the mass of some fragments of a compound.

How many carbon atoms are present in a molecule which gives an M+1 peak that is 11.48% of the intensity of the molecular ion?

11

What are the predicted m/z values (masses) and relative heights of all the molecular ions of 1-bromoethane that would appear on a mass spectrum (excluding peaks produced by ¹³C and ²H)?

M⁺ peak at m/z = 108 and an M+2 peak at m/z = 110
The M+2 peak is approximately the same height as the M+ peak.

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

M + 2 peak

Which of the following gives rise to a prominent M − 15 peak in the mass spectrum?

3- methycyclopentane

Which of the following is the definition of the base peak of a mass spectrum?

the peak corresponding to the most abundant ion

Which of the following sets of molecular ions does an alkyl bromide possess?

two molecular ions in a 1:1 ratio separated by two mass units

Which of the following gives rise to a prominent M − 15 peak in the mass spectrum?

methylcyclopentane

Which of the following bonds of the octane radical cation is least subject to fragmentation?

i

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

 

It has the highest m/z value of all the peaks in the spectrum.

 

It has the largest peak height in the spectrum.

 

The m/z value corresponds to a very stable carbanion.

 

The m/z value equals the molecular weight of the compound.

 

The base peak is assigned a relative abundance equal to that of the parent ion.

It has the largest peak height in the spectrum.

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

98

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

from two ¹³C's

Which compound would show a larger than usual M+2 peak in the mass spectrum?

CH₃CH₂SCH₃

Which C-C bond would most likely break and give fragments in the mass spectrum of butyl benzene?

2

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

loss of an electron

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

88, 73, 43

The mass spectrum of which compound has an M+2 peak that has intensity that is about 25% of its M⁺ peak?

3-chloropentane

Which of the following gives rise to a prominent peak in the mass spectrum with m/z of 45?

hexanoic acid

Which of the following gives rise to a prominent M − 18 peak in the mass spectrum?

cyclohexanol

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

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

m/z	Intensity
84	10.00
85	0.56
86	0.04

C₅H₈O

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

57

Which of the following fragment peaks would not be present in the mass spectrum of n-hexane?

87

For toluene (shown below), you would expect to see which m/z fragment in the mass spectrum?

15