A DFT Analysis of the Molecular Structures of Nitrophenoxathiin Compounds

The influence of nonbonding intramolecular interaction of the nitro group, on the tendency by which its sigma- and pi-withdrawing characters can affect the puckering of the phenoxathiin nucleus is investigated. The structure of the selected nitrophenoxathiins is predicted with the help of density functional calculations using the B3LYP/6-31+G(d) model. The magnitude of change in the puckering angle of phenoxathiin is found to be dependent on the orientation attained by the nitro groups, which determines the extent by which the pi-withdrawing character of the nitro group operates on the phenoxathiin nucleus. The in-plane nitro group in position-2 and -3 and the partially twisted nitro in position-1 induce flattening on the phenoxathiin nucleus while the out-of-plane nitro group in position-4 induces further puckering on the phenoxathiin nucleus. Successive substitution by nitro groups at these positions enhances these effects. 1,8-Dinitrophenoxathiin is predicted to be the least puckered while 4,6-dinitrophenoxathiin is the most puckered in the dinitro-series. Few examples of tetranitrophenoxathiins are investigated and prove to follow the same trends. The encountered changes are analyzed in terms of the changes in the hybridization of the substituted carbon atom. The HOMO and LUMO frontier orbitals of the studied compounds are presented.