dft calculations on 1-hetero-2,5-cyclohexadiene-1-oxide: molecular structure and stability

Molecular structures of 1-hetero-2,5-cyclohexadiene-1-oxide, X_O, are studied and compared with their corresponding deoxygenated compound, 1-hetero-2,5-cyclohexadiene, X, using DFT at B3LYP/6-311++G** level. The most stable boat conformers are found for O_O, S_O, Se_O, P_O, As_O, S, Se, N, P, As, and the most stable planar conformers are also found for NO, C_O, Si_O, Ge_O, O, C, Si, Ge. Isodesmic reactions to determine the stabilities of X_O and X are considered. Nuclear independent chemical shifts, NICS, are calculated for the investigation of the homo-aromatic character of X_O and X. The optimised geometries show the bonding in the molecules is explicable in terms of basic chemical concepts. The atomic charges calculated are also reasonable based on the concepts of electronegativity and conjugation.