Modern Analytical Techniques Flashcards
Mass spectronomy process
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
Fragmentation equation
Free radical cation —> cation + free radical
Common fragment Mr
CH3+ = 15
C2H5+ = 29
C3H7+ = 43
C4H9+ = 57
What does mass spectronomy peak height imply
Increase height/abundance
Increase stability
Name and describe two commonly stable mass spectronomy groups
Carbocations
- alkyl group have stabilising +be inductive effect
Acylium
- stabilising 2 structure resonance
M + 1 peak
C13 peak
Small
No. C = (M+1 height) / (M height) X100
M + 2 peak
Halogen
Cl37
Br81
How to identify molecules using mass spectronomy
Compare to known spectra data
Acyl chlorides
Haloalkanes
CA
Ketone
Aldehydes
Alcohols
Infrared spectroscopy theory
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
Two possible effects of IR absorption
Stretching, change bond length
Bending, change bond angle
Carbonyl IR peak
1700
Strong, sharp peak
Alcohol IR peak
3500
Strong, broad
Amide IR peak
3300
Strong, sharp
Describe the IR spectra graph
Y = % transmission
X = waveNUMBER (1/wavelength)
Higher number/NRG/bond strength/frequency
Lower number/NRG/bond strength/frequency
IR spectra impurities
IR spectra indicates extent/nature of impurities
Impurities absorb IR in bonds
Unexpected peaks
Compare to pure sample spectra
IR fingerprint region
RHS
1500-500
Complicated absorptions
Identify diff molecules/isomers
Compare to known compound spectra
Why are C13 and H1 used in nuclear magnetic resonance
Odd no. Nucleons
Have spin
Weak mag field
Behaviour in larger magnetic field
TMS uses
Standard substance
Chemical shift value/Delta = 0
ppm relative to TMS
Used for calibration
Why is TMS used for calibration
12 hydrogens in identical environments
Single intense absorption peak
4 carbon in identical environments
Single absorption peak
Inert
Non-toxic
Volatile (easily removed)
Nucleus environments
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
C13 NMR
No. Diff carbon environments in a molecule
One peak for each carbon environment
H1/proton NMR
Each hydrogen nuclei environemnt has one peak
Relative area under each peak indicates relative no. Of H atoms in the environment
Dissolving samples for H1/proton NMR
Solvent that doesn’t have any H1 atoms
Deuterated solvents (H replaced by D/H2), no spin
CCl4
Proton/H1 NMR splitting patterns
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
Uses of NMR
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
HPLC stationary phase
Small solid particles packed into a column
Eg. Silica bonded to various HCs
HPLC mobile phase
Polar liquid mixture
Eg. Water/methanol
Column chromatography HPLC process
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)
HPLC retention time
Time for substance to pass through column and reach detector
Increase solubility, increase speed
Gas chromatography stationary phase
Inert gas stream
Gas chromatography mobile phase
Coiled column coated in viscous liquid/oil
Column chromatography process and a use
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)
Chromatography/mass spec combination
Gas/HPL chromatography = separate
MS = identify sample
Chromatography/mass spec nuclei alignment
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
High resolution mass spectra
RIM to 4/5 DP
Differentiate between compounds with same molar mass
Use given 4/5 DP data to calculate
