Energetic and Structural Studies of Two Biomass-Derived Compounds: 6- and 7-hydroxy-1-indanones

The energetic study of 6-hydroxy-1-indanone and 7-hydroxy-1-indanone was performed using experimental techniques and computational calculations. The enthalpies of combustion and sublimation of the two compounds were determined and allowed to derive the corresponding gas-phase standard molar enthalpies of formation. For this purpose, static-bomb combustion calorimetry and drop-method Calvet microcalorimetry were the experimental techniques used. Further, the enthalpy of fusion of each compound was obtained from scanning differential calorimetry measurements. Additionally, the gas-phase standard molar enthalpies of formation of these compounds were calculated through high-level ab initio calculations. The computational study of the molecular structures of the indanones was carried out and two possible conformers were observed for 6-hydroxy-1-indanone. Furthermore, the energetic effects associated with the presence of one hydroxyl group as a substituent on the benzenic ring of 1-indanone were also evaluated. Both experimental and theoretical methods show that 7-hydroxy-1-indanone is thermodynamically more stable than the 6-isomer in the gaseous phase and these results provide evidence for the existence of a strong intramolecular H-bond in 7-hydroxy-1-indanone. Finally, the intramolecular proton transfer in 7-hydroxy-1-indanone has been evaluated and as expected, it is not energetically favorable.