Modern Analytical Techniques I Flashcards
What can be obtained from a mass spectrum?
Information about the molecular structure of an organic molecule
What is the first thing to look for in a mass spectrum?
The peak due to molecular ion - normally has highest m/z value
What is the molecular ion peak a result of?
Result of the organic molecules losing an electron in the mass spectrometer
What is the M+1 peak caused by?
Caused by the presence of carbon-13 isotope
What are the peaks with smaller m/z value a result of?
Fragmentation in the mass spectrometer, rearrangement reactions and the loss of more than one electron.
What does the ionisation process do to the molecular ion?
Causes the molecular ion to be in a high-energy state
What are the two fragments that many ions break into?
A neutral species (radical) and a positive ion
How can a functional group be identified?
A functional group causes molecules to breeze a apart in a characteristic way.
Common fragment lost? 15, 17, 28, 29, 31 ,45, 77
15- CH3+ 17- OH+ 28-CO+. 29- C2H5, CHO+ 31-CH20H+ 45-COOH. 77-C6H5
What fragments can be derived from ethane?
Forms a methyl cation and methyl radical
What fragments can be derived from propane?
A methyl cation and ethyl cation in its spectrum
Are radicals detected in mass spectrometer? So..
They are not detected so all the peaks formed by fragmentation are caused by positive ions.
What does the base peak demonstrate?
Ion with highest abundance + most stable fragment
What’s happens when some molecules absorb infrared radiation?
Vibrations which stretches (bond length increase or decrease) or Bends (bond angle increases or decreases)
What is linked to absorption of infrared radiation?
Changes in polarity of molecules. So simple non-polar molecules (H2 OR CL2) Do not absorb IR
When does stretching occur?
When a bond absorbs IR and uses it to alter the length of the bond
What is transmittance value in IS?
The amount of radiation absorbed at a particular wave number
What does the wave number of an infrared absorption represent?
The frequency of IR absorbed by a particular bond in a molecule
What does the intensity of an Infrared absorption describe?
Amount of IR absorbed.
What is the correlation between intensity and transmittance?
Weak intensity = high transmittance value vice versa
What are the 3 mains ways of using infrared spectra?
Predicting spectrum of organic compound
Deducing the functional group from a list of wave numbers
Deducing the structure from molecular formula and wave number
