On malonaldehyde and acetylacetone: are theory and experiment compatible?

For malonaldehyde (MA) and acetylacetone (AcAc) the available experimental structural and spectroscopic data are briefly summarized and contrasted with extensive ab initio calculations of their salient features. Attention is directed to a clear discrepancy between ab initio computed stability of the two degenerate structures of enol AcAc (as published, and confirmed in this report) and the observed species populations. MA and AcAc are prototypes of a unique class of compounds for which significant differences in structure are anticipated for small differences in thermochemical parameters. Temperature dependent FTIR spectra were recorded; the latter confirm that a discrepancy exists.