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