17.1 Mass Spectrometry
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What happens to an organic compound when it is placed in a mass spectrometer?
It loses an electron and forms a positive ion. Called a molecular ion.
What does a mass spectrometer detect?
The mass-to-charge ratio (M/Z) ratio of the molecular ion, which gives the molecular mass of the compound.
How do you find the molecular mass from a mass spectrum?
Find the M+ peak on the right hand side of the graph. It is the CLEAR peak.
What is the small peak 1 after the M+ mass?
The small proportion of the molecules that will have a Carbon-13 atom instead of a carbon-12 atom.
What is fragmentation?
When some molecular ions break down into smaller fragments during mass spectrometry
What are other peaks in a mass spectrum caused by?
Fragment ions, formed from the breakdown of the molecular ion.
What should a simple fragmentation do? (what should it form?)
Break down a molecular ion into a radical and a positively charged fragment ion.
Why is the mass spectrum of each compound unique? (including isomers)
Because molecules will all fragment in slightly different ways depending on their structures
How does a mass spectrometer work?
1- Sample is placed in mass spectrometer 2- Sample is vaporised, then ionised to form positive ions 3- Ions are accelerated, heavier ions move more slowly, but all molecules have the same kinetic energy 4- Ions are detected on a mass spectrum as a mass-to-charge ratio (M/Z)