Modern Analytical Techniques

Question 1

Mass spectronomy process

Answer 1

Sample vaporised
e- gun removes e-s —> cations
Cations accelerated
Pass through -ve grid
Mag curved field
Increase speed with higher charge/lesser size
M/Z ratio counter
Uncharged fragments not detected
Relative abundance
Mr of sample
RFM of molecule using molecular ion

Question 2

Fragmentation equation

Answer 2

Free radical cation —> cation + free radical

Question 3

Common fragment Mr

Answer 3

CH3+ = 15
C2H5+ = 29
C3H7+ = 43
C4H9+ = 57

Question 4

What does mass spectronomy peak height imply

Answer 4

Increase height/abundance
Increase stability

Question 5

Name and describe two commonly stable mass spectronomy groups

Answer 5

Carbocations
- alkyl group have stabilising +be inductive effect
Acylium
- stabilising 2 structure resonance

Question 6

M + 1 peak

Answer 6

C13 peak
Small
No. C = (M+1 height) / (M height) X100

Question 7

M + 2 peak

Answer 7

Halogen
Cl37
Br81

Question 8

How to identify molecules using mass spectronomy

Answer 8

Compare to known spectra data
Acyl chlorides
Haloalkanes
CA
Ketone
Aldehydes
Alcohols

Question 9

Infrared spectroscopy theory

Answer 9

All molecule bonds vibrate
Some absorb IR
To absorb IR must be covalent/polar
Different bonds absorb different wavelengths
Bonds in different environments absorb different wavelengths

Question 10

Two possible effects of IR absorption

Answer 10

Stretching, change bond length
Bending, change bond angle

Question 11

Carbonyl IR peak

Answer 11

1700
Strong, sharp peak

Question 12

Alcohol IR peak

Answer 12

3500
Strong, broad

Question 13

Amide IR peak

Answer 13

3300
Strong, sharp

Question 14

Describe the IR spectra graph

Answer 14

Y = % transmission
X = waveNUMBER (1/wavelength)
Higher number/NRG/bond strength/frequency
Lower number/NRG/bond strength/frequency

Question 15

IR spectra impurities

Answer 15

IR spectra indicates extent/nature of impurities
Impurities absorb IR in bonds
Unexpected peaks
Compare to pure sample spectra

Question 16

IR fingerprint region

Answer 16

RHS
1500-500
Complicated absorptions
Identify diff molecules/isomers
Compare to known compound spectra

Question 17

Why are C13 and H1 used in nuclear magnetic resonance

Answer 17

Odd no. Nucleons
Have spin
Weak mag field
Behaviour in larger magnetic field

Question 18

TMS uses

Answer 18

Standard substance
Chemical shift value/Delta = 0
ppm relative to TMS
Used for calibration

Question 19

Why is TMS used for calibration

Answer 19

12 hydrogens in identical environments
Single intense absorption peak
4 carbon in identical environments
Single absorption peak
Inert
Non-toxic
Volatile (easily removed)

Question 20

Nucleus environments

Answer 20

Nucleus can be partly shielded from external magnetic field effects by surrounding e-s
Absorb different NRG amounts/frequencies in different environments
Eg. Bonded to electronegative atom, higher e- density around atom, less shielding, higher frequency of radio waves absorbed

Question 21

C13 NMR

Answer 21

No. Diff carbon environments in a molecule
One peak for each carbon environment

Question 22

H1/proton NMR

Answer 22

Each hydrogen nuclei environemnt has one peak
Relative area under each peak indicates relative no. Of H atoms in the environment

Question 23

Dissolving samples for H1/proton NMR

Answer 23

Solvent that doesn’t have any H1 atoms
Deuterated solvents (H replaced by D/H2), no spin
CCl4

Question 24

Proton/H1 NMR splitting patterns

Answer 24

Peaks split into smaller peaks
Multiplets (singlet, doublet, triplet, quartet)
Peaks split into no. Hs on neighbouring Cs + 1
N + 1 rule
OH/NH peaks don’t split only CH
Spin-spin coupling effect

Question 25

Uses of NMR

Answer 25

Identifying unknown compounds
MRI
- Protons in water, make up large % human body
- 3D body imaging
- Harmless
- Radio waves and magnetic fields don’t damage cells

Question 26

HPLC stationary phase

Answer 26

Small solid particles packed into a column
Eg. Silica bonded to various HCs

Question 27

HPLC mobile phase

Answer 27

Polar liquid mixture
Eg. Water/methanol

Question 28

Column chromatography HPLC process

Answer 28

Mobile phase into column under high pressure
Mixture to be separated goes into a solvent stream
Sample must be have high bp or be heat sensitive
Mixture attracted to solid by differing amounts
UV passed through
UV detector —> chromatogram
(Solvent pump, sample injector, HLPC column, UV detector, chromatogram/waste)

Question 29

HPLC retention time

Answer 29

Time for substance to pass through column and reach detector
Increase solubility, increase speed

Question 30

Gas chromatography stationary phase

Answer 30

Inert gas stream

Question 31

Gas chromatography mobile phase

Answer 31

Coiled column coated in viscous liquid/oil

Question 32

Column chromatography process and a use

Answer 32

Constantly dissolve in oil/adsorb onto solid
Evaporate, re dissolve through column
Chromatogram shows retention time
Area under peak = relative amount
Find alcohol level in blood
(Carrier gas, flow controller, sample injector, thermostatic oven, column, detector, chromatogram/waste)

Question 33

Chromatography/mass spec combination

Answer 33

Gas/HPL chromatography = separate
MS = identify sample

Question 34

Chromatography/mass spec nuclei alignment

Answer 34

Ransoms pin direction, cancel out mag field
External mag field = nuclei align with/against
NRG aligned with mag field < NRG aligned opposed
Nuclei absorb and emit radio waves between NRG levels
Opposed = emit, slip to lower level
With = absorb, flip to higher level
Initially more nuclei aligned with mag field, overall NRG absorption

Question 35

High resolution mass spectra

Answer 35

RIM to 4/5 DP
Differentiate between compounds with same molar mass
Use given 4/5 DP data to calculate