Thermochemical study of some cubane derivatives

The thermochemical study of cubane-1,4-dicarboxylic acid (1), diethyl cubane-1,4-dicarboxylate (2), diisopropyl cubane-1,4-dicarboxylate (3), and bis(2-fluoro-2,2-dinitro)ethyl cubane-1,4-dicarboxylate (4) was performed. The standard enthalpies of combustion (Delta(c)H degrees) and formation (Delta(f)H degrees) of these compounds were estimated using the method of combustion in a calorimetric bomb in an oxygen atmosphere. Using the additive group method, calculated values for Delta(f)H degrees of these substances which agreed satisfactorily with the experimental ones were obtained. The strain energies (E(S)) of the cubic structure of derivatives 1-4 were calculated. It was concluded that E(S) did not change on substitution of hydrogen atoms in cubane for various functional groups and was equal to E(S) of the structure of cubane itself. The reliability of the single published value of Delta(f)H degrees in the cubane crystal state, 541.8 kJ mol(-1) (129.5 kcal mol(-1)), was confirmed.