Quantum mechanical study of substituted phenoxathiin II: A study of the structure of phenoxathiin diazonium compounds

The structure of phenoxathiin diazonium compounds is studied to deduce the effect exerted by the σ- and π-electron withdrawing properties of the diazonium group on the puckered phenoxathiin nucleus. The study predicts and analyzes the configuration of several yet to be synthesized phenoxathiin diazonium compounds. The ab initio method at the B3LYP/6-31+G(d) basis set level of calculation is employed in this study. The diazonium group is predicted to induce noticeable changes on the geometry of the phenoxathiin nucleus, that are reflected on the puckering angle Φc of phenoxathiin. The magnitude of the change is found to be dependent on the position of the diazonium group with respect to the sulfur atom of the central heterocyclic ring. Substitution at the 1-position, ortho to the sulfur induces the least flattening effect on the nucleus, while substitution at the 3- position, para to the sulfur induces the highest flattening. Introduction of a second diazonium group enhances these effects. Phenoxathiin-1,9-bis(diazonium) is found to be the most puckered. On the other hand phenoxathiin-3,7-bis(diazonium), phenoxathiin-4,6-bis(diazonium), phenoxathiin-1,4-bis(diazonium), and phenoxathiin-2,3-bis(diazonium) are predicted to be absolutely planar. The inversion barriers for the puckered molecules under study are found to be quite small; ranging between 0.0012 and 0.92 kcal/mol.