Enthalpies of formation of dihydroxybenzenes revisited: Combining experimental and high-level ab initio data

Abstract

Accurate values of standard molar enthalpies of formation in condensed phases can be obtained by combining high-level quantum chemistry calculations of gas-phase enthalpies of formation with experimentally determined enthalpies of sublimation or vapourization. The procedure is illustrated for catechol, resorcinol, and hydroquinone. Using W1-F12, the gas-phase enthalpies of formation of these compounds at T=298.15K were computed as (−270.6, −269.4, and −261.0)kJ·mol−1, respectively, with an uncertainty of ∼0.4kJ·mol−1. Using well characterised solid samples, the enthalpies of sublimation were determined with a Calvet microcalorimeter, leading to the following values at T=298.15K: (88.3±0.3)kJ·mol−1, (99.7±0.4)kJ·mol−1, and (102.0±0.9)kJ·mol−1, respectively. It is shown that these results are consistent with the crystalline structures of the compounds.