Question 1

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 corresponds to the Br-79 isotope, and the M+2 peak corresponds to the Br-81 isotope. These peaks are approximately the same height due to the similar natural abundance of the two isotopes.

Question 2

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

Accepted Answer

The fragmentation pattern of n-hexane would not generate a peak at m/z 87.

Question 3

When a compound contains a sulfur atom, its mass spectrum contains a larger than usual ________ peak.

Accepted Answer

Sulfur has a significant natural abundance of the isotope 34S, which is two mass units heavier than the most common isotope 32S. This results in a noticeable M+2 peak in the mass spectrum.

Question 4

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

Accepted Answer

The answer of Which of the following structures is consistent...

Question 5

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

Accepted Answer

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

Question 6

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 7

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 signifies an odd number of nitrogen atoms because nitrogen has an odd atomic mass.

Question 8

Account for fragments having a m/z value of 45 and 55 in the mass spectrum of 2-hexanol by drawing structures of the fragments.

Accepted Answer

The answer of Account for fragments having a m/z value...

Question 9

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

Accepted Answer

The answer of What spectroscopic technique can be used to...

Question 10

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

Accepted Answer

The answer of In a mass spectrum, what m/z value...

Question 11

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

Accepted Answer

The answer of What compound has a significant m/z 70...

Question 12

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

Accepted Answer

The compound 3-bromopentane contains bromine, which has two isotopes, ^79Br and ^81Br, with nearly equal natural abundance. This results in M+ and M+2 peaks of approximately equal intensity in the mass spectrum.

Question 13

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 amu) during fragmentation in mass spectrometry, resulting in a prominent M-18 peak.

Question 14

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

Accepted Answer

The answer of Describe the molecular ion region in the...

Question 15

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

Accepted Answer

The answer of 2-Methylhexane shows an intense peak in the...

Question 16

At what m/z would the base peak of (E)-2-hexene occur?

Accepted Answer

The base peak in a mass spectrum is the tallest peak, which represents the most abundant fragment ion. To determine the base peak for (E)-2-hexene, we need to consider the possible fragmentation pathways of the molecule. One common fragmentation in mass spectrometry is the loss of a methyl group (CH3). If (E)-2-hexene loses a methyl group, it would form a 1-pentenyl cation (C5H9+). This cation could then lose a hydrogen ion (H+) to form a stable allyl cation (C3H5+), which would likely be observed as the base peak in the mass spectrum. The mass of the allyl cation is 55 amu, so the correct answer is C.

Question 17

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 % abundance of the peak at m/z 112.

Accepted Answer

The answer of The natural abundances of chlorine's two major...

Question 18

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 19

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 20

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.

Quiz 12: Infrared Spectroscopy and Mass Spectrometry

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) ?

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

When a compound contains a sulfur atom, its mass spectrum contains a larger than usual ________ peak.

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

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

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

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

Account for fragments having a m/z value of 45 and 55 in the mass spectrum of 2-hexanol by drawing structures of the fragments.

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

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

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

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

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

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

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

At what m/z would the base peak of (E) -2-hexene occur?

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 % abundance of the peak at m/z 112.

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

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], ________.

Quiz 12: Infrared Spectroscopy and Mass Spectrometry

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) ?

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

When a compound contains a sulfur atom, its mass spectrum contains a larger than usual ________ peak.

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

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

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

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

Account for fragments having a m/z value of 45 and 55 in the mass spectrum of 2-hexanol by drawing structures of the fragments.

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

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

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

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

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

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

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

At what m/z would the base peak of (E) -2-hexene occur?

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 % abundance of the peak at m/z 112.

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

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], ________.

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) ?

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

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 % abundance of the peak at m/z 112.

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], ________.