Chapter 17 Flashcards

1
Q

What is the molecular ion? How is it written?

A
  • The ion formed when an organic compound loses an electron and forms a positive ion in a mass spectrometer
  • Is often written as M^+
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2
Q

Show how the molecular ion of propan-1-ol is formed.

A
  • CH3CH2CH2CH2OH -> CH3CH2CH2CH2OH+ + e-
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3
Q

Where is the molecular ion peak found?

A
  • It is the peak the furthest right on a mass spectrum
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4
Q

What peak can sometimes be found beyond the molecular ion peak, and why?

A
  • The M+1 peak
  • It exists due to the fact that 1.1% of carbon atoms exist as carbon-13 (for example, a small proportion of propanol molecules will contain an atom of carbon-13, and so their molecular mass will be 61 instead of 60)
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5
Q

What is fragmentation?

A
  • The breaking down of molecular ions into smaller pieces known as fragments in a mass spectrometer
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6
Q

What do molecular ions break down into? Give an example.

A
  • In the simplest fragmentation, a molecular ion breaks down into a positively charged fragment ion and a radical
  • CH3CH2CH2CH2OH+ -> CH2OH+ + ·CH2CH3
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7
Q

What are the other peaks in a mass spectrum caused by?

A
  • Fragment ions
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8
Q

What can mass spectrometry be used for, and how?

A
  • To help identify molecules
  • From the fragment ions, as these will be different between molecules
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9
Q

What are the m/z of the hydroxide, methyl, ethyl, propyl and butyl fragment ions?

A
  • 17
  • 15
  • 29
  • 43
  • 57
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10
Q

How do you show the difference between the m/z of the molecular ion and fragment ions?

A
  • You show the molecular ion as M+, and the rest as m/z
  • The M+1 peak is also shown as M+1
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11
Q

What kind of motion do covalent bonds naturally have?

A
  • They vibrate around a central point, either by bending or stretching
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12
Q

What does infrared radiation do to covalent bonds?

A
  • It supplies them with more energy, so they bend/ stretch more
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13
Q

What restriction is there on the absorption of IR by covalent bonds?

A
  • Bonds can only absorb radiation of the same frequency as their natural frequency
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14
Q

How is the absorption of IR by covalent bonds used by chemists?

A
  • They use it to identify functional groups in organic molecules
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15
Q

List 3 things to be aware of when interpreting an infrared spectrum.

A
  • The fingerprint region
  • Broad peaks
  • C-H peak
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16
Q

What is the fingerprint region?

A
  • The fingerprint region is below 1500/cm, where there are several peaks
  • However, each molecule has a unique fingerprint region
17
Q

How can the fingerprint region be used to identify a molecule?

A
  • It can be ran through a database
18
Q

What is a broad peak?

A
  • A peak that is U-shaped rather than having a sharp point
19
Q

Which peak is broad (but isn’t shown as broad on the data sheet)?

A
  • OH for alcohol
20
Q

How do you identify functional groups using infrared spectroscopy?

A
  • First give the wavenumber range/s
  • Use to identify bond/s present
  • Using this information you can say the functional group/s (common trick is having an alcohol and a ketone as this can be mistaken for a carboxylic acid)
21
Q

What is important about a C-H peak?

A
  • It is usually not worth identifying as it is in almost all organic molecules
  • It is often confused with the OH bond from alcohols
22
Q

What happens when IR radiation enters the atmosphere?

A
  • It originally passes through the atmosphere and gets to the Earth’s surface, where most of it is absorbed
  • Some of it is re-emitted as longer wavelength IR radiation
23
Q

What issue does the re-emission of IR radiation cause?

A
  • Greenhouse gases (water, carbon dioxide and methane) have the same natural frequency as this IR radiation, and therefore absorb it
  • They then re-emit this radiation, which increases the temperature close to the Earth’s surface (global warming)
24
Q

What are 2 uses of infrared spectroscopy?

A
  • Breathalysers detect ethanol levels
  • Remote sensors monitor gases causing air pollution