The enthalpy of formation of dibenzofuran and some related oxygen-containing heterocycles in the gas phase. A GAUSSIAN-3 theoretical study

The discrepancies between the three experimental determinations of the enth alpy of formation of dibenzofuran have prompted us to carry out a theoretic al study. Standard ab initio molecular orbital calculations were performed using the recently proposed GAUSSIAN-3 theory. Owing to the size of the dib enzofuran molecule, calculations were carried out at the G3(MP2)//B3LYP lev el. Delta (f)H(m)degrees values of dibenzofuran and a series of related oxy gen-containing heterocycles have been calculated through atomization reacti ons, bond separation isodesmic reactions and other isodesmic processes. The averaged calculated Delta (f)H(m)degrees value, 12.4 +/- 1.6 kcal mol(-1), is inconclusive, and two of the three experimental values (R. Sabbah and I . Antipine, Bull. Soc. Chim. Fr., 1987, 392; R. Sabbah, Bull. Soc. Chim. Fr , 1991, 350 and R. D. Chirico, B. E. Gamman, S. E. Knipmeyer, A. Nguyen, M. M. Strube, C. Tsanopoulos and W. B. Steele, J. Chem. Thermodyn., 1990, 22, 1075), are equally acceptable.