The structure of 4-phenyl-2,6-bis(trifluoroacetyl)cyclohexanone and its dilithium salt in the crystal state, solution and gas phase

Abstract

4-Phenyl-2,6-bis(trifluoroacetyl)cyclohexanone and its dilithium salt were synthesized starting from the commercially available 4-phenylcyclohexanone. With X-ray structure analysis of these compounds, for the first time the solid state structure determination for a fluorinated 1,3,5-triketone and an alkaline salt of 1,3,5-triketone was achieved. The subsequent multinuclear NMR and MS investigations revealed that in solution and gas phase, analogously to the crystal, both compounds exist predominantly in a highly delocalized double U-enol(ate) form. The carbonyl O…O distances in the dilithium salt were established to be considerably longer than the distances between oxygens of the parent 1,3,5-triketone, bonded by strong (short) resonance assisted hydrogen bonds. Among the 1,3,5-tricarbonyl compounds with known crystal structure, the entitled 1,3,5-triketone shows comparatively weak delocalization over the conjugated bis-enolone backbone.