Quantum mechanical study of substituted phenoxathiin: A study of the structure of fluorinated phenoxathiins

The effect induced by introducing electron captor substituent, namely, fluorine in the arene rings of phenoxathiin on the structure of the phenoxathiin nucleus have been studied using the ab initio method at the B3LYP/(6-31+G)+d basis set level. The study predicts and analyses the configuration of several not yet synthesized fluorinated-phenoxathiin derivatives. Thus, the magnitude of change in the puckering angle Φc of phenoxathiin was found to be dependent on the position of the fluorine atom with respect to the oxygen atom of the central heterocyclic ring. Substitution at the 1-position, meta to the oxygen did induce flattening of the nucleus i.e. increased Φc, while substitutions at the 2- and 4- positions, para and ortho to the oxygen, respectively, induced further puckering on the nucleus i.e. decreased Φc. Successive substitution at these positions enhanced these effects. Thus, 1,9-difluorophenoxathiin was found to be the most flattened, while 2,3,4,6,7,8-hexafluorophenoxathiin was found to be the most puckered fluorinated phenoxathiins. The predicted inversion barrier for all the studied compounds was very small; it did not exceed 1.67 kcal/mol for the most puckered isomer. Consequently, we anticipated these compounds to enjoy an easy butterfly interconversion.