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A2 Chemistry - Unit 4 > Unit 3.4.11 - Structure Determination > Flashcards

Unit 3.4.11 - Structure Determination Flashcards

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1
Q

What is the main use of mass spectrometry?

A

To find the MR of a compound.

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2
Q

How many stages is mass spectrometry split into?

A

Five.

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3
Q

Name the five stages in mass spec?

A

Vaporisation Ionisation Acceleration Deflection Detection

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4
Q

What happens during vaporisation in mass spec?

A

The sample is heated so it is vaporises into a gas.

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5
Q

What happens during ionisation in mass spec?

A

High energy electrons are fired out of an electron gun towards the sample to knock off electrons and turn them into ions.

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6
Q

What happens during acceleration in mass spec?

A

Positive ions are reflected by an electric field.

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7
Q

What happens during deflection in mass spec?

A

The ions are deflected around the bend by a magnetic field.

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8
Q

Are heavier or lighter ions deflected more?

A

Lighter

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9
Q

What happens during detection in mass spec?

A

The magnetic field strength is increased so that different ions can reach the detector. When ions hit the detector they cause a current to flow. The bigger the current produced the more of that isotope present in the sample.

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10
Q

To find the Mr of a compound which peak do you look at?

A

Molecular Ion peak.

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11
Q

What is the molecular ion peak also known as?

A

The M peak

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12
Q

Why is the Mr of compound the same as the molecular ion peak?

A

The ion produced has a +1 charge so the mass/charge value of the M peak is the same as the molecular mass.

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13
Q

Does the M peak have the highest mass/charge ratio?

A

No, you get M+X peaks.

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14
Q

What is the M+1 peak due to?

A

The carbon - 13 isotope.

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15
Q

What can you use the M+1 peak for?

A

To find out how many carbon atoms there are in a molecule.

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16
Q

What formula relates the M+1 peak to the number of carbon atoms in a molecule?

A
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17
Q

When do you find M+2 peaks? And why?

A

If a molecule has chlorine or bromine in it because they have naturally occurring isotopes too.

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18
Q

What are chlorines 2 isotopes?

A

Cl-35 and Cl-37

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19
Q

What ratio do Cl-35 and Cl-37 occur in? How does this relate to the peaks?

A

3:1 so the M and the M+2 peaks will have heights in that ratio.

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20
Q

What are bromines 2 isotopes?

A

Br-79 and Br-81

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21
Q

What ratio do Br-79 and Br-81 occur in? How does this relate to the peaks?

A

Equal amounts so the M and the M+2 peak will have the same height.

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22
Q

Other than M, M+1 and M+2 what other peaks do you find? Why?

A

M+4 if molecules contain two atoms of the same halogen.

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23
Q

What causes the molecular ion to break up during mass spec?

A

The bombarding electrons.

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24
Q

What do fragments produce in a mass spec?

A

Fragmentation patterns.

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25
Q

Why do some fragment ions have higher peaks on a mass spec?

A

They are more stable so are more likely to form.

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26
Q

Name two stable fragment ions.

A

Carbocations and Acylium ions.

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27
Q

Why are carbocations more stable than other ions?

A

The Alkyl groups push electron density towards the positive charge to stabilise the ion, the more alkyl groups, the more stable.

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28
Q

What is a carbocation?

A

An ion with a positively charged carbon ion.

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29
Q

What is the chemical symbol for Acylium ion?

A

RCO+

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30
Q

What is an Acylium ion formed from?

A

Aliphatic ketones

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31
Q

What is meant by the resonant form of an Acylium ion?

A

There are two different possible structures and there is resonance between the two structures.

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32
Q

What helps to stabilise an Acylium ion?

A

The resonance.

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33
Q

What happens during infrared spectroscopy?

A
  1. A beam of IR radiation is passed through a sample. 2. The IR radiaton is absorbed by the covalent bond in the molecule increasing their vibrational energy. 3. Bonds between different atoms absorb different frequencies of IR radiation and bonds in different places of the molecule absorb different frequencies. 4. infrared spectroscopy produces a graph that shows what frequencies have been absorbed. 5. You can compare these frequencies against the given tables to allow you identify a compound.
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34
Q

What is NMR short for?

A

Nuclear Magnetic Resonance.

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35
Q

What is NMR?

A

An analytical technique which provides you with information on the different environments of atoms in a molecule.

36
Q

What are the two types of NMR?

A

Carbon - 13 and Proton NMR

37
Q

What is another name for proton NMR?

A

Hydrogen NMR

38
Q

What does carbon - 13 NMR show you?

A

How the carbon atoms in a molecule are arranged.

39
Q

What does proton NMR show you?

A

How the hydrogen atoms in a molecule are arranged.

40
Q

Why do carbon - 13 and hydrogen have a weak magnetic field?

A

They have an odd number of nucleons which causes it to have nuclear spin and so causes a weak magnetic field.

41
Q

How does NMR work in five steps?

A
  1. A large external magnetic field is applied 2. When it is applied the nuclei all align either with the field or opposed to it. 3. Nuclei opposed to the external magnetic field can omit radio waves and change their spin down to the lower energy level and so become aligned with the field. 4. Nuclei that are aligned with the external magnetic field can absorb radio waves which gives them enough energy to change their spin up to the higher energy level and so become opposed to the field. 5. NMR works by measuring the strength of the magnetic field felt by the nuclei compare to the standard substance.
42
Q

What is the standard substance used in NMR?

A

TMS

43
Q

What is chemical shift?

A

The difference between the peaks produced by the compound and TMS.

44
Q

What chemical shift value does TMS have?

A

Zero

45
Q

Which direction will all other peaks be compared to TMS on an NMR graph?

A

To the left

46
Q

Why do some atoms lessen the effect of the external magnetic field produced by nuclear spin?

A

They cause shielding which lessens the effect.

47
Q

What does TMS stand for?

A

Tetramethylsilnane

48
Q

Give five reasons why TMS is used as a reference during NMR.

A

1, Contains one proton and one carbon environment and so will only produce one peak. 2. Non toxic 3. Inert 4. Volatile so easily removed 5. The methyl groups provide a lot of shielding so it produces an up field peak.

49
Q

What is the integration ratio?

A

The height of the peaks in proton NMR shows you the ratio of proton atoms in the different environments.

50
Q

What is splitting patterns?

A

In proton NMR the peaks are split into smaller peaks.

51
Q

What does splitting patterns show you?

A

The number of protons in the neighbouring carbon atom.

52
Q

If the peak is a singlet how many hydrogens are on the adjacent carbon?

A

Zero

53
Q

If the peak is a doublet how many hydrogens are on the adjacent carbon?

A

One

54
Q

If the peak is a triplet how many hydrogens are on the adjacent carbon?

A

Two

55
Q

If the peak is quartet how many hydrogens are on the adjacent carbon?

A

Three

56
Q

Does carbon-13 NMR or proton NMR give a more simple spectra?

A

Carbon-13

57
Q

What is the difference between low resolution NMR and high resolution?

A

High resolution shows peak splitting and the integration value, low resolution only shows the integration value.

58
Q

What do the solvents have to be for NMR? Why?

A

Proton free as protons would confuse the spectra.

59
Q

What is deuterium?

A

Hydrogen with a neutron so it doesn’t have nuclear spin.

60
Q

Name three solvents used in NMR?

A

D2O, CDCl3 and CCl4

61
Q

What is chromatography used for?

A

To separate different compounds out of a mixture.

62
Q

What are the two stages in chromatography called?

A

Mobile phase and Stationary phase.

63
Q

What are the two types of chromatography?

A

Column and gas liquid.

64
Q

Describe what column chromatography looks like.

A

A glass column packed with a solid (stationary phase) and then a mixture that is going to be separated is added to the top and allowed to drain through the column. A solvent is then added (mobile phase). This allows the components to separate out.

65
Q

What is a common stationary phase used in column chromatography?

A

Aluminium oxide coated with water.

66
Q

What factors cause compounds to separate out in column chromatography?

A

How soluble they are in the mobile phase and how strongly absorbed by the stationary phase.

67
Q

What is retention?

A

How strongly a compound is absorbed by the stationary phase.

68
Q

Do more soluble or less soluble compounds in the mobile phase pass out of the column quickest?

A

More soluble.

69
Q

What is retention time?

A

The time taken for a component to travel through the column.

70
Q

What are two uses of column chromatography in industry?

A
  1. Purifying organic products 2. Separating out useful products, unreacted chemicals and side products.
71
Q

Why would a compound spend longer in the stationary phase?

A

It is more strongly absorbed.

72
Q

What is the stationary phase in gas liquid chromatography?

A

Viscous liquid that coats the inside of a long tube - oil.

73
Q

What is the mobile phase in gas liquid chromatography?

A

An unreactive gas like nitrogen.

74
Q

Why is the tube coiled in gas liquid chromatography?

A

To save space.

75
Q

Describe how you would carry out gas liquid chromatography?

A

The sample is heated and then vaporised and then passed through a long tube within an oven.

76
Q

What does the retention time for gas liquid chromatography depend on?

A

How long the compound spends moving along with the gas in the mobile phase and how long it spends stuck to the viscous liquid in the stationary phase.

77
Q

What does the area under the graph in a gas liquid chromatogram show?

A

The relative amount of each compound in the mixture.

78
Q

When is gas liquid chromatography good to use? Why?

A

Mixture of volatile liquids because they can turn into gases easily.

79
Q

Name two uses of gas liquid chromatography?

A
  1. To find the level of alcohol in the blood or urine. 2. To find the proportion of esters of oils used in paints.
80
Q

What type of peak do alcohols (O-H) produce in an infrared spectra?

A

Strong, broad.

81
Q

What type of peak do Carboxylic (O-H) produce in an infrared spectra?

A

Medium, broad.

82
Q

Draw the standard subsatnce used in NMR.

A
83
Q

Draw a priamry, secondary and tertiary carbocation.

A
84
Q

Draw how an acylium ion swaps between its to forms.

A
85
Q

Draw examples of how propan-1-ol can split into fragments during NMR.

A
86
Q

What does a molecule split into during fragmentation in mass spec?

A

An ion and a free radical

A2 Chemistry - Unit 4 (11 decks)

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