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

• Thermochemistry of hydroxyphenols probed by experimental and theoretical methods.
• A new paradigm for obtaining enthalpies of formation of crystalline compounds.
• High-level ab initio results for the thermochemistry of gas-phase hydroxyphenols.
• Sublimation enthalpies of hydroxyphenols determined by Calvet microcalorimetry.

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 = 298.15 K were computed as (−270.6, −269.4, and −261.0) kJ · mol−1, respectively, with an uncertainty of ∼0.4 kJ · mol−1. Using well characterised solid samples, the enthalpies of sublimation were determined with a Calvet microcalorimeter, leading to the following values at T = 298.15 K: (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.

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