Assignment of the IR spectrum of 2 | 食品添加物合法業者資訊網

2018年1月28日—AssignmentoftheIRspectrumof2,4-pentanedione(acetylacetone)·The1728and1708stretchescorrespondtoC=Ostretchesintheketoform- ...

OH str for beta diketones is tabulated from 3200 to 2400 1/cm. The shift is explained by resonance of the hydrogen bonded structure.

Its absorption features is small or unseen as for

commonly the ketonic form is highly dominant; i.e. we wont expect to see OH str in the acetaldehyde spectrum, even

owing to the above mentioned resonance, the dipole change associated to symmetric OH str is null, and it is minimal for the AS one.

The symmetry of 2,4-pentanedione makes the last point even more important.

Concerning the second part. The fact that the O of the carbonyl of the enoform is H bonded does further shift down the related CO str. Moreover, in addition to resonance with the C=C, note that again there will be resonance with the CO in beta as above, and this further shift the frequency to lower wn.