Topic 19 - Modern Analytical Techniques 2

Question 1

What is high resolution mass spectrometry?

Answer 1

mass spectrometry which can measure Mr to 4 decimal places (more accurate)

Question 2

What can high resolution mass spectrometry be used for?

Answer 2

to distinguish between compounds that appear to have same Mr when rounded to a whole number

Question 3

What does NMR stand for?

Answer 3

nuclear magnetic resonance

Question 4

What is NMR (nuclear magnetic resonance)?

Answer 4

an analytical technique which uses a magnetic field to align protons in the nucleus of hydrogen atoms and carbon-13 atoms
-is used to determine structure of a compound

Question 5

What is used as a standard in NMR?

Answer 5

tetramethylsilane (TMS)

(CH3)4Si

Question 6

Why is TMS used as a standard/comparative peak in NMR?

Answer 6

• all 12 of its hydrogen atoms are in the same environment (no splitting pattern)
• all of its hydrogen atoms are more heavily shielded in any other molecule (aka their e- lie closer to the hydrogens than in any other molecule)
• it is inert
• its peak is to the right so doesn’t overlap with other peaks
• it has a low boiling temperature/is volatile so can be easily removed
• gives a strong signal so only a small amount needed

Question 7

What does C-13 NMR provide information about?

Answer 7

position of C-13 atoms in a molecule

Question 8

What does proton NMR provide information about?

Answer 8

positions of H atoms in a molecle

Question 9

What does low resolution NMR tell us?

Answer 9

• number of hydrogen environments

- number of hydrogen atoms in each hydrogen environment

Question 10

What does high resolution NMR tell us?

Answer 10

• number of hydrogen environments
• number of hydrogen atoms in each hydrogen environment
• how many hydrogens are on adjacent carbon

Question 11

What is the number of peaks on a NMR spectra equivalent to?

Answer 11

number of hydrogen environments

Question 12

What is the height of a peak on a low resolution NMR spectra equivalent to?

Answer 12

how many hydrogen atoms are in that environment

Question 13

What is the splitting pattern on a high resolution NMR spectra equivalent to?

Answer 13

the number of hydrogen atoms are on the adjacent carbon plus one
(N+1 rule)

Question 14

What is the area under a cluster on a high resolution NMR spectra equivalent to?

Answer 14

number of hydrogen atoms in environment

Question 15

How many hydrogens are on the adjacent carbon to a singlet?

Answer 15

0

Question 16

How many hydrogens are on the adjacent carbon to a doublet?

Answer 16

1

Question 17

How many hydrogens are on the adjacent carbon to a triplet?

Answer 17

2

Question 18

How many hydrogens are on the adjacent carbon to a quartet?

Answer 18

3

Question 19

How many hydrogens are on the adjacent carbon to a quintet?

Answer 19

4

Question 20

What do you call the splitting pattern when there are 0 carbons on the adjacent carbon?

Answer 20

singlet

Question 21

What do you call the splitting pattern when there is 1 carbon on the adjacent carbon?

Answer 21

doublet

Question 22

What do you call the splitting pattern when there are 2 carbons on the adjacent carbon?

Answer 22

triplet

Question 23

What do you call the splitting pattern when there are 3 carbons on the adjacent carbon?

Answer 23

quartet

Question 24

What is the N+1 rule?

Answer 24

the number of subpeaks within a cluster on a high resolution NMR is equivalent to the umber of hydrogen atoms on the adjacent carbon plus one

Question 25

What is the unit for chemical shift?

Answer 25

ppm

Question 26

What is chromatography?

Answer 26

a technique used to separate components of a mixture so that they can be identified -uses a mobile and stationary phase

Question 27

What types of chromatography are there?

Answer 27

- thin layer chromatography (TLC) - column chromatography - high performance liquid chromatography (HPLC) - gas chromatography (GC)

Question 28

What does TLC stand for?

Answer 28

thin layer chromatography

Question 29

What is the stationary phase in thin layer chromatography?

Answer 29

TLC plate coated in solid particles

Question 30

What is the mobile phase in thin layer chromatography?

Answer 30

solvent

Question 31

Rf =

Answer 31

distance moved by spot _____________________ distance moved by solvent

Question 32

What does the height a component move up thin layer chromatography depend on?

Answer 32

its interactions with the stationary phase | -ie. if its moved higher up, it has greater interactions with plate

Question 33

What is the stationary phase in column chromatography?

Answer 33

solid (eg. silica) which is packed into column

Question 34

What is the mobile phase in column chromatography?

Answer 34

solvent (which runs down column with gravity)

Question 35

Name examples of a polar solvent that could be used with a non-polar silica in column chromatography

Answer 35

water ethanol ethanoic acid

Question 36

Name examples of a non-polar solvent that could be used with a polar silica in column chromatography

Answer 36

hexane cyclohexane hydrocarbons

Question 37

What does HPLC stand for

Answer 37

high performance/pressure liquid chromatography

Question 38

What is the stationary phase in high performance liquid chromatography?

Answer 38

solid packed into column

Question 39

What is the mobile phase in high performance liquid chromatography?

Answer 39

solvent

Question 40

What happens in high performance liquid chromatography (HPLC)?

Answer 40

- solvent (and sample) are forced through horizontal column (packed with solid) under high pressure - detector at the end of column detects each compound and calculates its retention time (Rt)

Question 41

What does GC stand for?

Answer 41

gas chromatography

Question 42

What is the stationary phase in gas chromatography?

Answer 42

solid with high mp which is packed into column

Question 43

What is the mobile phase in gas chromatography?

Answer 43

inert gas (aka noble gas)

Question 44

What happens in gas chromatography (GC)?

Answer 44

- an inert gas (eg. noble gas) acts as a solvent and is forced through column (packed with a solid) under high pressure by a pump - sample is injected into the column as a gas (sample may have been heated and vaporised first depending on its standard state) and is forced through column - detector detects each compound and calculates its retention time (Rt)

Question 45

Why is the column in an oven in gas chromatography?

Answer 45

to ensure sample is maintained as a vapour

Question 46

What must the gas used as a solvent in gas chromatography be?

Answer 46

inert/not reactive | ie. noble gas eg. helium

Question 47

What must the solid used as the stationary phase in gas chromatography be?

Answer 47

have a high mp

Question 48

What are the advantages of high performance liquid chromatography (HPLC) and gas chromatography (GC)?

Answer 48

- faster - more accurate - can use smaller quantities

Question 49

What are the disadvantages of high performance liquid chromatography (HPLC) and gas chromatography (GC)?

Answer 49

-not so good at identifying components (∴ are used with mass spectrometry)

Question 50

Name two examples of when chromatography (HPLC/GC) is used with mass spectrometry

Answer 50

- forensics | - drug testing

Question 51

Why are chromatography (HPLC/GC) and mass spectrometry used together?

Answer 51

mass spectrometry can be used to identify the substances HPLC/GC have separated (instead of using a detector) as HPLC/GC are not so good at identifying