Question 1

Which of the following m/z values is the base peak for benzyl alcohol?

Accepted Answer

The base peak is the most intense peak in a mass spectrum. From the given m/z values, the peak with the highest intensity is 91, therefore, it is the base peak for benzyl alcohol.

Question 2

Which of the following structures will give a base peak of 43 in mass spectrometry?

Accepted Answer

Base peak in mass spectrometry is the most intense peak in the spectrum. The structure that generates the base peak of 43 will have a fragment with a mass of 43. Examining the given structures, only structure C has a possible fragmentation pattern that could generate a peak with a mass of 43. The fragment that would produce a peak of 43 is CH2=N-NH2+. Hence, option C is the correct answer.

Question 3

Provide the structure of the two ions which result when the molecular ion of 2-methoxypentane undergoes fragmentation by ^α-cleavage.

Accepted Answer

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Question 4

The mass spectrum of an unknown compound has a molecular ion peak with a relative abundance of 43.27% and an M + 1 peak with a relative abundance of 3.81%.How many carbon atoms are in the compound?

Accepted Answer

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Question 5

Which of the following is/are true about the MS of 1-bromobutane?

Accepted Answer

Peaks of approximately equal intensity are observed at m/z 136 and 138, indicating the presence of the molecular ion and its M+2 isotopomer. The major fragmentation occurs by cleavage of the C-Br bond, which leads to the formation of a butyl cation and a bromide anion. The most intense peak occurs at m/z 43, which corresponds to the butyl cation fragment.

Question 6

Describe the molecular ion region in the mass spectrum of CH₃CH₂Br.

Accepted Answer

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Question 7

Provide the structure of the species which results when the molecular ion of 4-heptanone undergoes fragmentation via a McLafferty rearrangement.

Accepted Answer

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Question 8

The mass spectra of alcohols often fail to exhibit detectable M peaks but instead show relatively large ________ peaks.

Accepted Answer

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Question 9

In the mass spectrum of bromoform,CHBr₃,molecular ion peaks appear at m/z 250,251,252,and 253? What is the ratio of the intensities of these peaks?

Accepted Answer

The ratio of the intensities of the peaks in the mass spectrum of bromoform (CHBr3) is determined by the natural isotopic abundance of bromine isotopes. Bromine has two stable isotopes, ^79Br and ^81Br, with natural abundances of approximately 1:1. When considering the three bromine atoms in bromoform, the combinations of these isotopes lead to molecular ions with different masses (250, 251, 252, and 253) and the pattern of their intensities follows the binomial distribution for three trials (n=3) with probabilities p=q=0.5, resulting in a 1:3:3:1 ratio.

Question 10

Which of the following compounds exhibits the pattern of m/z values shown below? 41,43,57,87,101,116

Accepted Answer

The pattern of m/z values indicates the presence of a tert-butyl group (m/z 57) and an isopropyl group (m/z 43), along with a bromine atom (m/z 87). The only compound among the options that contains both these groups, along with a bromine atom, is C, which is sec-butyl isopropyl ether. Therefore, C is the best choice.

Question 11

A compound shows a molecular ion peak at m/z 167.The relative intensities of the M and M+1 peaks are 50.0 and 4.4 respectively.How many carbons are in each molecule of the compound?

Accepted Answer

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Question 12

An acylium ion is often produced as a fragment in the MS of which of the following class of organic compounds?

Accepted Answer

Acylium ions are positively charged ions that have a carbon atom that bears a positive formal charge, a carbonyl group and a leaving group. They are often observed as a fragment in the mass spectrometry of ketones due to the ease with which the carbonyl group can be cleaved to form the acylium ion. The other compounds listed do not typically undergo fragmentation that leads to the formation of an acylium ion.

Question 13

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

Accepted Answer

The molecular weight of 2-chloropropane is 78 g/mol. The molecular ion peak in a mass spectrum represents the ion with the same mass as the molecular weight of the compound. Therefore, the m/z of the molecular ion peak in the mass spectrum of 2-chloropropane is 78.

Question 14

Show the m/z values of the molecular ion and 5 likely fragments for the compound ethyl ether, CH₃CH₂OCH₂CH₃

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Question 15

Which of the following m/z values is least intense in the mass spectrum of 1-chloropropane?

Accepted Answer

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Question 16

Which of the following is the base peak for the compound below?

Accepted Answer

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Question 17

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

Accepted Answer

The molecular weight of 1,2-dichloroethane is 98 g/mol (2 x 35.5 for chlorine atoms + 2 x 12.01 for carbon and 2 x 1.01 for hydrogen atoms). Therefore, the molecular ion peak of greatest intensity should correspond to the m/z ratio of 98. None of the other options are a possible molecular ion peak for this compound.

Question 18

What technique can be used to determine the molecular formula of a compound?

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Question 19

Is it possible to have an M + 2 peak in mass spectrometry? Explain.

Accepted Answer

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Question 20

Which compound's mass spectrum shows peaks at M,M+2,and M+4 whose abundances are in a ratio of 1:2:1?

Accepted Answer

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Quiz 13: Mass Spectrometry,infrared Spectroscopy,and Uvvis Spectroscopy