The Joining of Measurement and Prediction: The Enthalpy of Formation of 1,4-Cubanedicarboxylic Acid

This study is a multidisciplinary contribution to the thermochemistry of 1,4-cubanedicarboxylic acid (pentacyclo[4.2.0.0 2,5 .0 3,8 .0 4,7 ]octane-1,4-dicarboxylic acid). An isoperibolic static microbomb calorimeter was used to determine the enthalpy of formation in the condensed phase at T = 298.15 K as Δ f H m ° (cr) = (−355.9 ± 11.7) kJ·mol −1 . The enthalpy of sublimation was obtained by combining the vaporization enthalpy evaluated by correlation-gas chromatography and the fusion enthalpy measured by differential scanning calorimetry and adjusted to T = 298.15 K, which afforded the value Δ sub H m (298.15 K) = (126.5 ± 9.0) kJ·mol −1 . Combination of these two enthalpies gave Δ f H m ° (g, 298.15 K) = (−229.4 ± 14.8) kJ·mol −1 . Additionally the enthalpy of sublimation of 1-adamantanecarboxylic acid (tricyclo[3.3.1.1 3,7 ]decane-1-carboxylic acid) was determined as Δ sub H m (298.15 K) = (98.7 ± 4.5) kJ·mol −1 . By means of theoretical calculations using isodesmic reactions, the enthalpy of formation of 2,6-cuneanedicarboxylic acid (pentacyclo[3.3.0.0 2,4 .0 3,7 .0 6,8 ]octane-2,6-dicarboxylic acid) was calculated. Strain energies of cubane and cuneane dicarboxylic acids were also calculated.