Aromaticity and Magnetic Properties of 1- and 2-Indenones and Their Aza Derivatives
The almost unknown series of 1- and 2-indenones and their aza-derivatives have been analyzed with the aim of understanding the higher stability and aromaticity of the 1-one compared to the 2-one series. The effect of tetrafluorination of the six-membered ring on their relative stability and aromaticity and the corresponding 19F–19F spin–spin coupling constants (SSCC) have been analyzed for the compounds of these two series. Magnetic NICS and electronic PDI, FLU, and MCI aromaticity criteria, complemented by an energy decomposition analysis, allow the higher stability and aromaticity of 1-indenones compared with 2-indenones to be attributed to the π-component of the orbital interaction term. The reduced aromatic character of the 2-one series also provides an explanation for the 19F–19F SSCC observed in the tetrafluorinated 2-one compounds, which differ significantly from those of 1,2,3,4-tetrafluorobenzene.