Modern Analytical Techniques Flashcards

1
Q

Mass spectronomy process

A

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

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2
Q

Fragmentation equation

A

Free radical cation —> cation + free radical

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3
Q

Common fragment Mr

A

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

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4
Q

What does mass spectronomy peak height imply

A

Increase height/abundance
Increase stability

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5
Q

Name and describe two commonly stable mass spectronomy groups

A

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

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6
Q

M + 1 peak

A

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

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7
Q

M + 2 peak

A

Halogen
Cl37
Br81

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8
Q

How to identify molecules using mass spectronomy

A

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

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9
Q

Infrared spectroscopy theory

A

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

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10
Q

Two possible effects of IR absorption

A

Stretching, change bond length
Bending, change bond angle

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11
Q

Carbonyl IR peak

A

1700
Strong, sharp peak

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12
Q

Alcohol IR peak

A

3500
Strong, broad

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13
Q

Amide IR peak

A

3300
Strong, sharp

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14
Q

Describe the IR spectra graph

A

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

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15
Q

IR spectra impurities

A

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

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16
Q

IR fingerprint region

A

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

17
Q

Why are C13 and H1 used in nuclear magnetic resonance

A

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

18
Q

TMS uses

A

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

19
Q

Why is TMS used for calibration

A

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

20
Q

Nucleus environments

A

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

21
Q

C13 NMR

A

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

22
Q

H1/proton NMR

A

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

23
Q

Dissolving samples for H1/proton NMR

A

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

24
Q

Proton/H1 NMR splitting patterns

A

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

25
Q

Uses of NMR

A

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

26
Q

HPLC stationary phase

A

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

27
Q

HPLC mobile phase

A

Polar liquid mixture
Eg. Water/methanol

28
Q

Column chromatography HPLC process

A

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)

29
Q

HPLC retention time

A

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

30
Q

Gas chromatography stationary phase

A

Inert gas stream

31
Q

Gas chromatography mobile phase

A

Coiled column coated in viscous liquid/oil

32
Q

Column chromatography process and a use

A

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)

33
Q

Chromatography/mass spec combination

A

Gas/HPL chromatography = separate
MS = identify sample

34
Q

Chromatography/mass spec nuclei alignment

A

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

35
Q

High resolution mass spectra

A

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