Question 1

In a mass spectrum, what m/z value would correspond to the following fragment?

Accepted Answer

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Question 2

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

Accepted Answer

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Question 3

The natural abundances of chlorine's two major isotopes are ³⁵Cl (75.5%) and ³⁷Cl (24.5%). If the mass spectrum of chlorobenzene contains a peak at m/z 114 with an abundance of 15.0%, calculate the percent abundance of the peak at m/z 112.

Accepted Answer

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Question 4

What compound has a significant m/z 70 in its mass spectrum?

Accepted Answer

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Question 5

The presence of which element is indicated by a peak at m/z 127 and a characteristic 127-unit gap in the mass spectrum?

Accepted Answer

Iodine (I) has a significant isotope at mass number 127, which would cause a peak at m/z 127 in a mass spectrum. This characteristic makes it identifiable in mass spectrometric analysis.

Question 6

Consider 3-pentanone (shown below). What m/z fragments would you expect to see in the mass spectrum of this compound?

Accepted Answer

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Question 7

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

Accepted Answer

Alcohols often lose a water molecule (18 mass units) during fragmentation, resulting in a prominent M-18 peak in the mass spectrum.

Question 8

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

Accepted Answer

Compounds containing sulfur, like CH₃CH₂SCH₃, show a larger than usual M+2 peak due to the natural isotopic abundance of sulfur, which includes a significant amount of the heavier isotope, S-34.

Question 9

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

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Question 10

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 and²H)?

Accepted Answer

1-bromoethane contains bromine, which has two isotopes: Br-79 and Br-81. The M+ peak at m/z = 108 corresponds to the Br-79 isotope, and the M+2 peak at m/z = 110 corresponds to the Br-81 isotope. These peaks are approximately the same height due to the similar natural abundance of the two isotopes.

Question 11

If the mass spectrum of chlorobenzene shows a peak with an m/z value of 114, having an abundance of 15%, calculate the m/z value and approximate abundance of the molecular ion peak.

Accepted Answer

The answer of If the mass spectrum of chlorobenzene shows...

Question 12

The two most abundant isotopes of boron are ¹⁰B and ¹¹B, with ¹¹B being about 4 times more abundant. In the mass spectrum of trimethylborate [(CH₃O)₃B], ________.

Accepted Answer

The most abundant isotopes of boron are ^10B and ^11B, with ^11B being about 4 times more abundant than ^10B. In the mass spectrum of trimethylborate, which contains boron, the peak corresponding to the molecule containing ^11B (m/z 104) would be 4 times more intense than the peak for the molecule containing ^10B (m/z 103), reflecting the natural abundance ratio of these boron isotopes.

Question 13

The mass spectrum of which compound has an M+2 peak that has intensity that is about 4% of its M⁺ peak?

Accepted Answer

The answer of The mass spectrum of which compound has...

Question 14

The mass spectrum of which compound has M⁺ and M+2 peaks of approximately equal intensity?

Accepted Answer

Bromine has two isotopes, Br-79 and Br-81, with nearly equal natural abundance, leading to M+ and M+2 peaks of approximately equal intensity in the mass spectrum of compounds containing bromine, such as 3-bromopentane.

Question 15

Which of the following structures is consistent with the mass spectrum shown below?

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Question 16

2-Methylhexane shows an intense peak in the mass spectrum at m/z = 43. Propose a likely structure for this fragment.

Accepted Answer

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Question 17

An ________ molecular ion peak usually indicates the presence of an odd number of nitrogen atoms in the molecule.

Accepted Answer

An odd molecular ion peak occurs when the molecule loses an electron, resulting in an unpaired electron in the molecular ion. When a molecule contains an odd number of nitrogen atoms, the resulting molecular ion peak will also be odd.

Question 18

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

Accepted Answer

A fragment peak at m/z 87 would indicate the loss of a methyl group and a tertiary carbocation, which is not possible in n-hexane. The other fragment peaks listed (m/z 71, 57, 43, and 29) are all possible in the mass spectrum of n-hexane.

Question 19

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

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Question 20

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

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Quiz 12: Infrared Spectroscopy and Mass Spectrometry

In a mass spectrum, what m/z value would correspond to the following fragment?

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

The natural abundances of chlorine's two major isotopes are ³⁵Cl (75.5%) and ³⁷Cl (24.5%). If the mass spectrum of chlorobenzene contains a peak at m/z 114 with an abundance of 15.0%, calculate the percent abundance of the peak at m/z 112.

What compound has a significant m/z 70 in its mass spectrum?

The presence of which element is indicated by a peak at m/z 127 and a characteristic 127-unit gap in the mass spectrum?

Consider 3-pentanone (shown below) . What m/z fragments would you expect to see in the mass spectrum of this compound?

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

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

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

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 and²H) ?

If the mass spectrum of chlorobenzene shows a peak with an m/z value of 114, having an abundance of 15%, calculate the m/z value and approximate abundance of the molecular ion peak.

The two most abundant isotopes of boron are ¹⁰B and ¹¹B, with ¹¹B being about 4 times more abundant. In the mass spectrum of trimethylborate [(CH₃O) ₃B], ________.

The mass spectrum of which compound has an M+2 peak that has intensity that is about 4% of its M⁺ peak?

The mass spectrum of which compound has M⁺ and M+2 peaks of approximately equal intensity?

Which of the following structures is consistent with the mass spectrum shown below?

2-Methylhexane shows an intense peak in the mass spectrum at m/z = 43. Propose a likely structure for this fragment.

An ________ molecular ion peak usually indicates the presence of an odd number of nitrogen atoms in the molecule.

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

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

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

Quiz 12: Infrared Spectroscopy and Mass Spectrometry

In a mass spectrum, what m/z value would correspond to the following fragment?

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

The natural abundances of chlorine's two major isotopes are 35Cl (75.5%) and 37Cl (24.5%). If the mass spectrum of chlorobenzene contains a peak at m/z 114 with an abundance of 15.0%, calculate the percent abundance of the peak at m/z 112.

What compound has a significant m/z 70 in its mass spectrum?

The presence of which element is indicated by a peak at m/z 127 and a characteristic 127-unit gap in the mass spectrum?

Consider 3-pentanone (shown below) . What m/z fragments would you expect to see in the mass spectrum of this compound?

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

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

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

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) ?

If the mass spectrum of chlorobenzene shows a peak with an m/z value of 114, having an abundance of 15%, calculate the m/z value and approximate abundance of the molecular ion peak.

The two most abundant isotopes of boron are 10B and 11B, with 11B being about 4 times more abundant. In the mass spectrum of trimethylborate [(CH3O) 3B], ________.

The mass spectrum of which compound has an M+2 peak that has intensity that is about 4% of its M+ peak?

The mass spectrum of which compound has M+ and M+2 peaks of approximately equal intensity?

Which of the following structures is consistent with the mass spectrum shown below?

2-Methylhexane shows an intense peak in the mass spectrum at m/z = 43. Propose a likely structure for this fragment.

An ________ molecular ion peak usually indicates the presence of an odd number of nitrogen atoms in the molecule.

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

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

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

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

The natural abundances of chlorine's two major isotopes are ³⁵Cl (75.5%) and ³⁷Cl (24.5%). If the mass spectrum of chlorobenzene contains a peak at m/z 114 with an abundance of 15.0%, calculate the percent abundance of the peak at m/z 112.

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

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 and²H) ?

The two most abundant isotopes of boron are ¹⁰B and ¹¹B, with ¹¹B being about 4 times more abundant. In the mass spectrum of trimethylborate [(CH₃O) ₃B], ________.

The mass spectrum of which compound has an M+2 peak that has intensity that is about 4% of its M⁺ peak?

The mass spectrum of which compound has M⁺ and M+2 peaks of approximately equal intensity?

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