spectroscopy and chromatography Flashcards
what is mass spectrometry used for
To calculate the molecular mass of an organic compound and gives further information about its structure
what happens when a molecular ion splits up in mass spec
It forms a positive ion ie CH4+ and a radical ie CH2.
What happens when a molecule first splits up in mass spec
A positive ion is formed and an electron ie CH4+ + e-
What is the M+ peak
The peak with the highest m/z value, there may be a peak one unit after, this is the m+1 peak and is for isotopes. Its length with reflect its relative intensity
How are the other peaks in mass spec formed
The molecular ions break down into smaller peaks known as fragments, this is called fragmentation.
What is detected in the mass spec
The positive ion
How does infrared spectroscopy work
Certain bonds in a molecule absorb infra-red radiation at characteristic frequencies causing the covalent bond to shake.
Rf value
Distance moved by a component divided by distance moved by solvent.
Retention time
The time between injection and detection of a component
How is the mixture separated during gas chromatography
Solubility
What is the role of gas in gas chromatography
Mobile phase
What is the role of liquid in gas chromatography
Stationary phase
How can gas chromatogram be used to determine the percentage composition of each component in the mixture
Measure the area under each peak, find total area
%=(area of one peak/total area) x100
What is used as a solvent in proton NMR
A deuterated solvent because it would not give a peak as it does not contain H. Example, (CD3)SO
What is TMS used for?
A reference
What is D2O used for
In a process called proton exchange the OH peak will disappear. This helps differentiate between OH and NH peaks.
What is the fingerprint area
Below 1500 cm-1. This part of the spectrum is unique for each compound and can be compared to a computer database of the fingerprint area of known compounds to identify the compound.
What can infrared be used to detect
Functional groups
What are the uses of infrared in the real world
Breathalysers test for ethanol by using analysing an infrared spectroscopy
How is infrared associated with global warming
Water vapour, methane and carbon dioxide absorb longer wavelength IR radiation because it has the same frequency of the natural frequency of their bonds, C=O, O-H and C-H. Eventually the vibrating bonds re-emit this energy as radiation which increases the temperature of the atmosphere which leads to global warming.
What does carbon NMR tell us
The number of different carbon environments from the peaks and the types of carbon environments from the shift.
What will carbon NMR not tell us
If a compound is symmetrical and has the same atoms attached it will not tell us about the environments which are alike.
What does proton NMR tell us
Provides the number of different proton environments from the number of peaks. The type of proton environments from the chemical shift. The relative number of each type of proton from the integration number. The number of protons adjacent to the given proton from the splitting pattern.
What does a proton NMR not tell us
Two or more proton peaks will not show up if they are symmetrical and have the same groups attached
