[nate]

Can anyone tell me a good and methodical way to interpret IR spectra?  We are discussing them in class and the prof was good about telling us the mechanics behind the instrument but then just kind of threw us to the wolves and said, "What compound is represented by this IR Spectrum?"

Is it really just looking at each of the peaks and finding the ones that fit best?  There has to be a simpler way. . .right?

[mike]

You need a table of IR shifts. Many functional groups have characteristic IR signals, for example C=O (carbonyl) usually  have a signal around 1700cm^-1

[nate]

I've got the table, it just looks like alot of the peaks have "similar" absorption frequencies and are close for two possible structures.  I assume it just takes practice but, it seems like there would be a simpler way than plug-n-chug.

[mike]

Unless you are using some sort of database to help with the identification, I would think that you are simply using IR to help identify certain functional groups. I would be hard to deduce a structure simply from its IR, especially just visually. You would ususally use it either to characterise a compound that you are reasonably sure of anyway, or in conjuction with NMR spectra. Many of the common functional groups are quite easy to pick out of IR spectra: 1700 = carbonyl, 1700 + 3000 = carboxylic acid, >3100 = OH etc.