Pictorial Guide to Infrared Spectra

by James

in Spectroscopy

From the “I wish I made this” department….

Pictorial Guide to Infrared Spectra (Jon Chui, U. of Victoria, Canada)

Apparently Jon has been thinking about putting together a similar graphic for NMR, but hasn’t gotten around to it. Maybe if enough people nag and harass him, he’ll do it. Great work Jon.

List of common Infrared absorption frequencies (UCLA)

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Thank you for pointing us to this cool guide!

I want to make sure I’m reasoning correctly regarding the strength of different carbonyl bonds in the guide. Amides actually donate the extra electron pair to the carbonyl carbon, weakening the carbonyl bond. Because of acids’ acidic proton, the carbonyl loses its full double bond to resonance stabilization, thus the carbonyl’s stronger bond. Ketone has a weakly activating group attached on both sides, so it is the next weakest. Aldehyde only has it on one side, so its carbonyl is stronger still. Though ester’s extra oxygen donates electron pairs to the carbonyl, it is also strongly electronegative, thus it actually removes electrons from the carbonyl carbon, making the carbonyl bond more polar thus strongest of the carbonyls listed. Am I missing anything?


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