Infrared Spectrometry Flashcards
How do you find the relative molecular mass of a compound?
You look at the molecular ion peak (M+)
Which is the M+ peak?
The peak furthest on the right with the highest mass/charge ratio
Which is the M+1 peak?
The smaller peak to the right of the M+ peak
What are some uses of mass spectrometry?
Analysing molecules in space
Determining abundance of isotopes
Detecting banned substances
identifying unknown compounds
What is the mass spectrometry method?
Ionise sample
Accelerate into mass analyser
Ions deflected
Ions detected on spectrum generated by computer
What is fragmentation?
Excess energy from ionisation can be transferred to a molecular ion making it vibrate
This causes bond to weak and split ion into fragments
What does fragmentation produce?
Fragment of compound and free radical
How do you work out the structural formula of the fragment?
Look at m/z value of graph
Assume value of peak matches mass of ion
How do you work out the compound from the fragments?
Identify the fragments eg. OH group, CH3 group
Piece together to form a molecule with correct Mr
How do you work out number of carbon atoms?
Height M+1 peak
————————- X100
Height of M peak
What happens to bonds when they absorb IR?
Bend
Stretch
What does the peak on an IR spectrum show?.
Vibration of particular group
What do vibrations depend on?
Bond strength
Bond length
Mass of bonded atoms
What is the uses of IR spectrum?
Used in forensic science
Monitoring degree of unsaturation in polymers
Drug analysis
Breathalyzer
What is IR spectrum?
A plot of transmission of IR against wavenumber (1/wavenumber)
