THEORETICAL STUDIES ON HEATS OF FORMATION OF PYRIDINE N-OXIDES USING DENSITY FUNCTIONAL THEORY AND COMPLETE BASIS METHOD

Abstract

The heats of formation (HOFs) for 11 pyridine N-oxide compounds are calculated by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86, PBE1PBE) methods with 6-31G** basis set and ab initio CBS-4M method. It is demonstrated that the B3PW91 method is accurate to compute the reliable HOFs for pyridine N-oxide compounds. It is also noted that the HOF is the smallest for the pyridine N-oxide which has the substituent group on the para-position, such as 4-NC–c- C 5 H 4 NO , 4- H 2 NOC – C 5 H 4 N – O , and 4- HO 2 C –c- C 5 H 4 NO . In addition, we think that the HOF of 2- HO 2 C –c- C 5 H 4 NO is much larger than that of 3- HO 2 C –c- C 5 H 4 NO and 4- HO 2 C –c- C 5 H 4 NO , which may be the result of intramolecular hydrogen bond formation and further measurements are needed to reexamine the HOFs for 2- HO 2 C –c- C 5 H 4 NO , 3- HO 2 C –c- C 5 H 4 NO , and 4- HO 2 C –c- C 5 H 4 NO .