DFT Study and NBO Analysis of Conformational Properties of 2-Substituted 2-Oxo-1,3,2-Dioxaphosphorinanes and Their Dithia and Diselena Analogs

The conformational behaviors of 2-fluoro-2-oxo-1,3,2- (compounds 1-3), 2-chloro-2-oxo- 1,3,2- (compounds 4-6), 2-bromo-2-oxo-1,3,2- (compounds 7-9), -dioxa, -dithia, -diselena phosphorinanes have been analyzed by means of hybrid density functional theory (B3LYP/6- 311+G**) and ab initio molecular orbital (HF/6-311+G**) based methods and NBO interpretation. The results justified the axial conformations preference of compounds 1-9. The calculated relative energies ΔE0 and Gibbs free energy difference values (ΔGeq-ax) between the axial and equatorial conformations decrease from compound 1 to compound 3, from compound 4 to compound 6 and from compound 7 to compound 9. The NBO analysis showed the same trends for the accordingly calculated Generalized Anomeric Effect (GAE) values. The correlations between the GAE, dipole-dipole interactions, Wiberg Bond Index (WBI), orbital occupancies, HOMO, LUMO energies and structural parameters for rationalization of conformational behavior of compounds 1-9 have been investigated.