Experimental and computational thermochemistry of the isomers: Chromanone, 3-isochromanone, and dihydrocoumarin

Abstract

The standard ( p ∘ = 0.1 MPa) molar enthalpies of formation in the condensed state of chromanone, dihydrocoumarin, and 3-isochromanone were derived from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by combustion calorimetry. Calvet microcalorimetry was used to derive the standard molar enthalpies of sublimation and vaporization. Compound - Δ c U m 0 ( cr ,l ) /(kJ · mol −1) - Δ f H m 0 ( cr,l ) /(kJ · mol −1) Δ cr,l g H m 0 /(kJ · mol −1) Chromanone 4393.3 ± 1.6 289.1 ± 2.0 84.6 ± 1.3 Dihydrocoumarin 4364.6 ± 1.9 317.8 ± 2.2 69.9 ± 0.5 3-Isochromanone 4348.7 ± 1.4 333.7 ± 1.8 97.3 ± 1.4 From these values the standard molar enthalpies in the gaseous phase, at T = 298.15 K, were derived. Additionally estimates were performed of the enthalpies of formation of all the studied compounds in gas-phase, using DFT and other more accurate correlated calculations, together with appropriate isodesmic or homodesmic reactions. There is a reasonable agreement between computational and experimental results.