IR Spectral Analysis
The IR Spectrum
- A type of absorption spectrum
- Spectra contain "bands" (peaks) that
signify the presence of important functional groups or bonds.
- Commonly used for structure eluciation,
particularly in organic chemistry.
- Molecular vibrations responsible for IR absorption
Group Frequency vs. Fingerprint
Region
- See Infrared Spectroscopy in the Majors' Manual.
- Characteristic IR Absorptions
Bands Important in the Vanillin
Lab:
|
Functional Group or Bond |
Frequency (cm-1) |
Characteristics |
|
Hydroxy (-O-H) |
3200-3600 |
broad in liquid/solid phase |
|
Hydrocarbon (-C-H) |
2850-3000 |
. |
|
Carbonyl (-C=O) |
~1700 |
strong |
|
Methoxy (-C-O) |
1070-1200 |
strong |
Practice Interpreting These
Spectra
Predict the major IR bands you should see for
the following compounds. Also note bands which should be missing from the
spectra. Then follow the links to view the actual spectra. (Note: These are all gas phase spectra and will appear slightly different than the usual solid or
liquid phase spectra. Hydroxy bands, in particular, will be sharper -- because
of the absence of hydrogen bonding that will occur in the solid and liquid
phases.)
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