What to look for in an IR spectrum.

Consider the IR spectrum of propanol shown on the left.

Notice some of the key features, namely the:
-broad absorption trough at 3200 - 3550 indicating an O-H (alcohol)
- absorption trough at about 2850 - 3000 indicating an C-H bond
-absorption trough at about 1050 - 1100 indicating a C-O bond

Consider the IR spectrum of propanoic acid shown on the left.

Notice some of the key features, namely the:
-broad absorption trough at 2500 - 3300 indicating an O-H (acid)
- absorption trough at about 2850 - 3000 just poking out from under the O-H absorption trough, indicating an C-H bond
-absorption trough at about 1670 - 1750 indicating a C=O bond
- absorption trough at about 1300 indicating a C-O bond

Comparing the IR spectra of propanol and propanoic acid we can see how the O-H regions differ from an alcohol
   
   
   
Describe how IR spectroscopy can be used to work out which isomer is present in a sample by matching the spectra on the left with the molecules on the right.. Below are three isomers of a compound with molecular formula C4H8O2
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