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Chemistry 4 > Analysis of organic compounds > Flashcards

Analysis of organic compounds Flashcards

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1
Q

Give a description of the mass spectrometer.

A

Involves the interaction of the gaseous sample with high energy electron beam to form positive ions.
These cations are accelerated by an electric field and detected by a magnetic field.

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2
Q

What is the basis of technique for mass spectrometry?

A

The electron beam removes electrons, creating cations.
As a result of the presence of electric and magnetic fields, the cations move in a curved path dependent on the m/z ratio.

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3
Q

What are fragment patterns in mass spectrometry?

A

The cations formed when a molecule loses an electron can be unstable. Some of them break up into smaller fragments, where one fragment is a cation and the other an uncharged free radical.

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4
Q

What are the major uses of mass spectrometry? (4)

A
  • determine molar mass: by finding the molar mass of parent ion
  • identify isotopes of an element and % abundance
  • assist with identifying structures of molecules from fragmentation
  • determining RAM for an element
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5
Q

Is mass spectrometry quanitative or qualitative?

A

Qualitative

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6
Q

How is the data of mass spectrometry interpreted?

A

The peak with the highest m/z ratio is usually due to parent ion
Characteristic fragmentation patterns result from the break up of unstable parent ions and can be used to identify the structure of the molecule.

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7
Q

Why can mass spectrometry be difficult to interpret? (2)

A
  • presence of different isotopes

- fragmentation of molecule

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8
Q

What are the three stages of mass spectrometry?

A
  1. ionisation
  2. acceleration
  3. deflection
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9
Q

Describe stage three of mass spectrometry.

A

Cations enter the magnetic field and deflected.
This depends on their:
- mass: lighter the mass, greater the deflection
- charge: greater the charge, greater the deflection

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10
Q

What two factors form the m/z ratio in mass spectrometry?

A

Mass and charge.

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11
Q

What must eligible fragments have in mass spectrometry?

A

A positive charge.

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12
Q

Where is the parent molecular ion located on a mass spectrum?

A

The very end of the graph, making it the furthest peak.

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13
Q

What information does the highest peak on a mass spectrum provide?

A

The highest peak is known as the base peak.

This is the most common type of fragment.

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14
Q

What is one feature of an element that could make it have a higher molar mass than it should have in mass spectrometry?

A

If an isotope is present, the ion could have a higher molar mass then the parent ion. This must be accounted for by stating the isotope of this structure.

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15
Q

Can molecular fragments in mass spectrometry have a greater charge than +1?
Does this affect any of the results?

A

Yes the charge could be greater than +1.

This would mean the m/z ratio would have to be simplified, by dividing molar mass by the charge.

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16
Q

Give a description of IR spectroscopy.

A

Interaction of polar bonds in molecules with IR light.

Frequency absorbed depends on the nature of the bond.

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17
Q

How does the nature of a bond in IR affect the frequency absorbed? (2)

A
  • single bonds absorb a lower energy than a double bond between the same atoms
  • single bonds between heavy atoms absorb lower energy than bonds between lighter atoms
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18
Q

What is the basis of technique for IR spectroscopy?

A

IR causes the bonds in molecules to bend and stretch.

The degree to which they bend and stretch depends on the amount of energy they absorb, thus their functional group.

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19
Q

Is IR spectroscopy quanitative or qualitative?

A

Qualitative

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20
Q

How can the data of IR spectroscopy be interpreted?

A

The IR shows the frequncies absorbed by a molecule.
The functional groups can be identified by comparing IR spectrum to data booklet, as different functional groups absorb different amounts of frequency.

21
Q

What does a troph represent in an IR spectrum?

A

Tells us that a covalent bond is absorbing energy.

22
Q

What does a hydroxy functional group look like on an IR spectrum?

A

A broad deep trough at 3200 - 3600.
O-H (alcohol) at 3300 cm-1
No presence of peak at 1700

23
Q

What does a carboxylic acid functional group look like on an IR spectrum?

A

A broad deep trough at 3000 combined with a narrow trough at 1700
O-H (acid) at 3000 cm-1
C=O (acid) at 1700 cm-1

24
Q

What does an amine functional group look like on an IR spectrum?

A

A broad trough

25
Q

What is nuclear magnetic resonance?

A

The idea that radio waves are used to transform neutrons into a high energy state.

26
Q

Give a description of NMR.

A

Involves the interaction of nuclei of atoms in a strong magnetic field with radio wave energy.

27
Q

What is the basis of technique for NMR?

A

Energy is absorbed by nuclei with an odd number of protons/ neutrons. When this occurs, the nuclei are said to be in resonance.
Atoms in the same chemical environment are said to be equivalent and will have the same chemical shift.
Atoms in different chemical environments absorb different amounts of energy in order to change energy state.

28
Q

What are the major uses of NMR?

A

Provides qualitative information about C-H backbone of organic compounds.

29
Q

Is NMR quantitative or qualitative?

A

Qualitative

30
Q

How is the data of NMR interpreted?

A
  • the number of different signals indicates the number of different environments
  • the chemical shift for each signal allows for identification of the types of environments
  • signals to the very left of the graph are in very polar/ electronegative environments
31
Q

How does NMR work?

A

When a magnetic field is applied to a compound with an odd of nutreons, the protons align in a low energy state.
When radio waves are passed through, it forces protons into an high energy state (resonance). How much energy required is dependent upon the degree of shielding. Over time, nuclei tend to flip back to a lower energy spin. This releases a pulse of energy which is measured.

32
Q

What type of solvents should be used for NMR?

A
  • should be chemically inert
  • should not contain protons
    eg heavy water (Dideuterium monoxide)
33
Q

What are the three types of NMR?

A
  • high-resolution 1H NMR
  • low-resolution 1H NMR
  • 13C NMR
34
Q

How is the data of low-resolution 1H NMR interpreted?

A
  • no of peaks: no of environments
  • chemical shift: position on x-axis
  • integration under peak: height ratio
35
Q

How is the data of high-resolution 1H NMR interpreted?

A
  • no of peaks: no of environments
  • chemical shift: position on x axis
  • integration under peak: height ratio
  • data on neighbouring atoms
36
Q

How does shielding effect nuclei’s ability to resonate?

A

Protons in non-polar environments need more energy to resonate as they are said to be shielded (protected) as electron clouds are closer to their nucleus.
Protons in polar environments need less energy to resonate as they are said to be shielded as the electronegative pulls electrons closer to its nucleus. Hence nucleus is more vulnerable/ exposed and therefore radio waves are more easily absorbed.

37
Q

What is chemical shift?

A

The difference in energy needed to change spin state in a sample is compared to the energy needed to change spin states in TMS.
Measured in ppm.

38
Q

What is 13C NMR?

A

Gives us information about the different chemical environments around each carbon atom.

39
Q

What is high-resolution 1H NMR?

A

Contains the same info as the low-resolution, but each signal appears to have been split into several peaks.
The no. of peaks in the high-resolution spectrum tells you about the number of hydrogen atoms next to the hydrogen atom that has produced that signal.

40
Q

What rule is needed for high-resolution 1H NMR?

A

Number of peaks= (number of neighbouring protons)+1

41
Q

Give a description of HPLC.

A

Is an analytical technique to separate, identify, and quantify components in a mixture.

42
Q

What does HPLC involve?

A

The substance being analysed is passed through a column containing a mobile phase and a stationary phase.
The mobile phase is the liquid which carries the sample through the colour and over the solid stationary phase.

43
Q

What are the major uses of HPLC?

A
  • provides qualitative and quantitative information on substance
  • useful for separating components with high molar masses
  • useful for identifying components with high molar masses
44
Q

Is HPLC quantitative or qualitative?

A

Both qualitative and quantitative.

45
Q

How is the data of HPLC interpreted?

A

the concentration of a component can be determined by comparing the area under its peak with that of standard solutions.

46
Q

How does separation in HPLC occur?

A

Separation occurs as a result of the differing abilities of the components to adsorb to the stationary phase and desorb onto the mobile phase.

47
Q

What does the retention time represent in HPLC?

A

Time is taken for the component to pass through the column. Each component passes through at a different rate due to the differences in their ability to adsorb and desorb to the SP and MP, allowing their identity to be revealed.

48
Q

What information can be gathered from a substance that has a long retention time?

A

The substance bonded to the stationary phase quiet strongly hence moved at a slower rate through the column.

Chemistry 4 (7 decks)

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