[wutkung]

I have been looking for the answer for the question, why is the C=O in dibenzalacetone has lower frequency than the standard C=O, which is about 1700cm-1

My guess is that it has something to do with the other double bonds that form when dehydration occurs and 2 water molecules are removed, or maybe it was the C=C stretching within the 2 phenyl groups.

Hopefully you guys are not too busy answering tons of questions including this one!  

[ATMyller]

Dibenzalacetone has conjucated system reaching troughout the whole molecule so the C=O double bond is actully more like a 1.5 bond due the delocalized electrons.