C17 - Spectroscopy Flashcards
What happens during mass spectrometry?
When placed in the spectrometer, the organic compound loses an electron and forms a positive ion, the molecular ion.
The mass spectrometer detects the mass-to-charge ratio of the ion which gives it’s molecular mass.
How do you find the molecular mass from the mass spectrum?
The molecular ion (M+) peak has to be located.
This is a clear peak with the highest mass-to-charge ratio on the right side of the spectrum.
A small peak to the right of the molecular ion peak is the M+ 1 peak, present due to isotopes of the compound.
What’s fragmentation?
When the mass spectrometer breaks molecular ions into smaller fragments.
These other peaks are called fragment ions.
Fragmentation usually forms a positive ion and radical by homolytic fission (only the ion appears on the spectrum)
What is infrared radiation used for?
It helps identify the types of bonds present in a compound and so can identify the functional groups and, with mass spec, the organic molecule.
How does infrared spectroscopy work?
Infrared radiation of 200-4000cm-1 is passed through the sample and is absorbed by bonds in the compounds.
This causes the bonds to stretch and bend, the amount of which depends on the strength of the bond and mass.
The amount of infrared absorbed and remitted is then analysed to identity the type of bonds and functional groups.
(Unit is wave number cm-1)
What’s the fingerprint region of an IR spectrum?
Peaks below 1500cm-1 which can identify a particular molecule.
What does an -OH functional group look like on an IR spectrum?
A broad peak from 2500-3300cm-1
What does a C=O functional group look like on an IR spectrum?
A narrow, sharp peak from 1630-1820cm-1
What is mass spectrometry used for?
To identify the molecular mass of an organic compound and gain information on its structure.
