VIBRATIONAL STUDIES OF METHYL-DERIVATIVES OF MALONALDEHYDE - DETERMINATION OF A RELIABLE FORCE-FIELD FOR BETA-DICARBONYL COMPOUNDS

The mid-infrared spectroscopy of methyl derivatives of malonaldehyde, acetylacetone and acetyl-acetaldehyde, isolated in argon and xenon mat rices is investigated, leading to new data for the vibrational analysi s of beta-dicarbonyl compounds. The experimental data are compared to force field calculations where the force constants are those obtained for malonaldehyde from local spin density calculations. The good agree ment between experimental and calculated frequencies shows that this m ethod correctly takes into account the electronic delocalization due t o the hydrogen bonding and to the conjugation between the double bonds in the pseudo-cycle of such compounds.