IR spectra for un unknown substance?

Steven Brooks · Sep 25, 2012

Hello Members,

Infrared spectra are used by chemists to help identify an unknown substance. Atoms in a molecule that are bound together by a particular bond vibrate at a predictable frequency, and light at that frequency is absorbed strongly by the atom. What is the IR spectra for un unknown substance?

Thanks and Regards,
Steven Brooks

stef · Sep 25, 2012

Compare it with the known spectras, if it aint match any then you have an unknown spectra.
:6:

telectrix · Sep 25, 2012

i has a vauxhall spectra once. easily identifiable as a recycled beer can.

Richard Burns · Sep 25, 2012

If you have an unknown material and you produce an IR spectrum for that material, you should be able to identify some of the specific groups that are present by the dips in the spectrum at specific wavelengths.

The presence of water will mask a lot of the early dips as it is strongly IR absorbent.
you can identify C=O groups, C-H, C-C, C=C etc. and this can start to give you the molecule composition.
I seem to remember that C=O is at about 1400 depending on the attached groups that can shift it somewhat.