Mass/ Infrared spec Flashcards

1
Q

What is mass spectrometery used for?

A
  • Mass spectrometery is used to find the relative molecular mass (Mr) of a compound.
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2
Q

What do all the peaks on a mass spectrometer trace show, what does the last peak/ peak(s) show?

A
  • Peaks show fragments of original molecule.
  • Last peak = M+1 peak OR molecular ion peak.
  • Molecular ion peak is the same as the relative molecular mass of original molecule.
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3
Q

When is high resolution mass spectrometery useful?

A
  • Useful when identifying different molecules that have the same molecular mass, rounded to the nearest whole no.
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4
Q

What do high resolution mass spectrometers do compared to low resolution mass spectrometers?

A
  • Measure the relative atomic/ molecular mass to several decimal places unlike standard low resolution MS –> may only be able to measure relative mass to nearest whole no.
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5
Q

What does IR spectroscopy do?

A
  • IR spectrosopy uses infrared radiation to increase the vibrational energy of covalent bonds in a sample.
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6
Q

True or False

Every covalent bond will absorb the same frequency of infrared radiation.

A
  • False!
  • Each covalent bond will absorb infrared radiation at characteristic wavenumbers, specific to the bond. (frequency of infrared.)

() - extra info for clarification.

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7
Q

What does the frequency of infrared radiation absorbed by a covalent bond depend on?

A
  • The atoms that are either side of the bond.
  • The position of bond in a molecule.
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8
Q

What is the “fingerprint region” of a spectra from infrared spectroscopy?

A
  • Finger print region is the part of the spectra that allows us to identify a specific molecule.
  • Fingerprint spectra lies between 500cm⁻¹ and 1500cm⁻¹.
  • The size and position of the peaks in fingerprint region are specific to specific molecule.
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9
Q

What can you do when you have determined the fingerprint region of a molecule?

A
  • Compare the fingerprint region generated against a known library of spectra to identify the molecule.
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10
Q

You have identified fingerprint region for unknown molecule, you compare this region to your library of spectra and find that it is similar to ethanoic acid but there are a few extra peaks, why are these extra peaks present in your spectra?

A
  • Extra peaks in fingerprint region indicates impurities in the sample.
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11
Q

What does “fingerprinting” in infrared spectroscopy allow for?

A
  • ‘Fingerprinting’ allows identification of a molecule by comparison of spectra.
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12
Q

Describe the greenhouse effect.

A
  • EM radiation is absorbed by Earth. Some of this radiation is re-emitted as infrared.
  • Greenhouse gases will absorb infrared radiation- trapping heat.
  • It is the covalent bonds in the greenhouse gases that actually absorbs the infrared radiation.
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13
Q

Give the 3 main greenhouse gases.

A

CH4
CO2
H20

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14
Q

What leads to global warming?

A
  • Human activities ie. burning fossil fuels , lanfills = larger volume of greenhouse gases entering atmosphere.
  • More infrared radiation/ heat trapped in atmosphere.
  • Gradual warming of Earth = global warming.
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15
Q

What is fragmentation during mass spectrometery?

A
  • Fragmentation is the breaking of 1 covalent bond in an ionised molecule, forming smaller ions and radicals.
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16
Q

What is the difference between peaks due to fragments/ molecular ion peaks?

A
  • Molecular ion peaks = FULL POSITIVE molecule has been detected.
  • Fragments= positive PARTS of molecule have been detected (but not full molecule.)
17
Q

What different peaks would you find on mass spectrometer trace for Cl2?

A
  • Molecular ion peaks: 70,72, 74.
  • Peaks due to fragmentation: 35, 37
18
Q

What is the OVERALL equation for fragmentation during mass spec? What will be detected by the mass spectrometer?

A
  • M⁺⋅ –> X⁺ + Y⋅
    ⋅ –> shows unpaired electron
  • Mass spectrometer will detect M⁺⋅ and X⁺ (the molecular ion peak and your fragments.)
19
Q

Why do the peaks furthest to right indicate Mr of molecular ion? How about if you have isotopes?

A
  • Without isotopes, single peak furthest to right = Mr of molecular ion (because this is greatest peak detcted/ FULL molecular ion ALWAYS has to be detected!)
  • With isotopes, it would be more than 1 peak, so you would calculate the Mr by calculating an average.
20
Q

Determine the m/z values for the MOELCULAR ION PEAKS (not fragments) of CH₃Cl. What are the relative abundances?

A

(CH₃³⁵Cl) ⁺ : m/z = 50
(CH₃³⁷Cl) ⁺: m/z = 52
Relative abundances –> 3:1 respectively

21
Q

Mass spec using CH₃Cl: Write fragmentation equation for peak at m/z 15.

Refer to Gautum notes (29/01/25) if needs be!

A

(CH₃Cl)⁺⋅ –> (CH₃)⁺ + Cl⋅

22
Q

Mass spec using CH₃Cl: Write fragmentation equation for peak at m/z 37.

A

(CH₃³⁷Cl)⁺⋅ –> CH₃⋅ + ³⁷Cl⁺

23
Q

C = 12.001
O = 15.998
S = 32.0025
A substance has precise Mr of 44.0035, determine its molecular formula.

precise masses here are just made up!

24
Q

If you are given an infrared spectrum of a molecule, and the table for wavenumber of bonds, where would you look to find the bonds present in the molecule?

A
  • Left hand side of the spectrum.
  • The “troughs” (ie. bottom parts) are considered as peaks, look at wavenumber for particular peaks and see what bond range they fall into.
25
Q

What is a carbonyl?

A
  • Aldehyde/ ketone.
26
Q

Why do carboxylic acids/ alcohols have broad absorptions?

A
  • They have broad absorptions due to hydrogen bonding.
27
Q

What different SHAPES of peaks are there for O-H’s, C=C, C=O?

Refer to printed diagram from shcool notes.

A
  • O-H - alochols - smooth peak (towards far left.)
  • O-H - acids- : jagged peak.
  • C=C: sharp intense peak.
  • C=O: sharp intense peak