Effect of heterosubstituent and ring puckering angle on linear and nonlinear properties of exo-insaturated four-membered heterocycles, Y=CCH2CH2X: a comparative ab initio, DFT and semi-empirical study

Abstract

ABSTRACTThe influence of heterosubstituent and ring puckering angle (ϕ) on electronic properties (μ, α, β and γ) of 16 four-membered heterocycles (1–16) were demonstrated theoretically using ab initio (HF and MP2), density functional theory (DFT) (PBE1PBE, SVWN5 and B3LYP) and semi-empirical (PM6 and PM3) treatments. Comparing the DFT and ab initio methods, these showed a similar description of electric dipole moment (μ) and polarisability (α) for each one of the studied heterocycles, with small differences in the prediction of α. The calculated hyperpolarisabilities (β and γ) are very sensitive to the quality of level theory, especially when the heterocycles contain phosphorus and sulphur. On the other hand, comparing with the rest of methods used, the semi-empirical calculations show significant deviations in the prediction of the different properties, and only are in agreement with the calculations of μ for the heterocycles that do not contain phosphorus or sulphur. In general, β and γ are more sensitive to the molecular geometry than μ and α. The dipole moment is determined by the heteroatom (X) within the ring, where the oxetanes and thietanes exhibit a minimum value of μ at planar conformations, while the azetidines and phosphetanes at axial conformations. All heterocycles show a minimum value of α at planar conformation, and their largest values are associated to conformations highly puckered. β exhibits an implicit relationship with the C = Y bond according to the conformational states. In addition, the X and Y heterosubstituents affect significantly the values of α, β and γ, observing the largest values for the phosphorus- and sulphur-containing heterocycles. Finally, considering the values obtained for α, β and γ, the studied heterocycles can represent an interesting unit for the design of new promising push–pull systems as donor or acceptor group.