Topic 8: IR/mass spectroscopy Flashcards
(20 cards)
Give modes of vibration for IR spectroscopy
1) Symmetric stretching
2) Asymmetric stretching
3) Scissoring
4) Rocking
Define IR spectroscopy
- When light frequency + resonance frequnecy of moleculer vibration = molecule absorbs energy = signal
- Can measure absorbance + transmittance % = usually trasnmittance
How to recognize alkane?
- C-H = just below 3000
- Hard to distingush between 2 different alkanes with IR
How to recognize alkenes?
- C-H = just below 3000
- =C-H = just above 3000
- C=C = around 1600
How to recognize alkynes?
- C-H = just below 3000
- ≡C-H = around 3200
- C≡C = 2000-2500
How to recognize aromatic compounds?
- Ar-H = just over 3000
- C=C = around 1600
How to recognize alcohols?
- O-H = wide = 3300-3400
- C-H = just below 3000
How to recognize amines?
- Depends on which amine = how many N-H
- N-H = 3200-3500 = number of peaks = how many N-H
- C-H = just below 3000
- C=C = if benzene = 1600
How to recognize aldehydes
- C-H = just below 3000
- O=C-H = 2 peaks = 2700/2800
- C=O = 1700
How to recognize ketones?
- C-H = just below 3000
- C=O = 1700
How to recognize carboxylic acids?
- O-H = very wide stretch at 3000
- C=O = 1700
How to recognize esters?
- C-H = just below 3000
- C=O = 1700
- C-O = 1200
Define mass spectrometry
- Measure mass of atoms/fragments of organic molecule
- ## Detect isotopes + abundance
Describe the mass spectrometer process
1) Sample injected into ionization chamber = vaporizes
2) Goes through e- gun = hit by high energy e- = removes e- forming +ve charge fragment
3) Accelerated towards electromagnet
4) Charged fragments deflect = heavier less than lighter = travel according to mass
5) Neutral fragments = not deflected
6) Fragments = hit detector = signal to computer = analysis
What is the energy of the e- gun?
70 eV
Define molecular ion peak
- Far right peak = molecular weight
Define base peak
- Highest intensity peak = most stable fragment
Define M+1 peak
- 1% abundance
What is the abundance of Cl isotopes?
- Cl35 = 75%
- Cl37 = 25%
- Signal at 62/64 = intensity pattern 3:1
Describe the pattern for alcohols
- Lose water = M-18 peak
