High-Level ab Initio Enthalpies of Formation of 2,5-Dimethylfuran, 2-Methylfuran, and Furan

A high-level ab initio thermochemical technique, known as the Feller-Petersen-Dixon method, is used to calculate the total atomization energies and hence the enthalpies of formation of 2,5-dimethylfuran, 2-methylfuran, and furan itself as a means of rationalizing significant discrepancies in the literature. In order to avoid extremely large standard coupled cluster theory calculations, the explicitly correlated CCSD(T)-F12b variation was used with basis sets up to cc-pVQZ-F12. After extrapolating to the complete basis set limit and applying corrections for core/valence, scalar relativistic, and higher order effects, the final Delta H-f degrees (298.15 K) values, with the available experimental values in parentheses are furan -34.8 +/- 3 (-34.7 +/- 0.8), 2-methylfuran -80.3 +/- 5 (-76.4 +/- 1.2), and 2,5-dimethylfuran -124.6 +/- 6 (-128.1 +/- 1.1) kJ mol(-1). The theoretical results exhibit a compelling internal consistency.