Electronic and spatial structure of five-membered oxygen-or sulfur-containing cyclic phosphorus and arsenic compounds based on quantum-chemical calculations

Abstract

We have carried out nonempirical quantum-chemical calculations for five-membered heterocyclic molecules containing O or S atoms and also P or As atoms in the ring, using RHF/6-31G(d) and MP2/6-31G(d) methods with full optimization of their geometry. We have studied their electronic and spatial structure and the characteristics of the interaction between atoms in the molecules.Keywords: five-membered oxygen-or sulfur-containing cyclic phosphorus and arsenic compounds, quantum chemical calculations, electronic and spatial structure.For oxygen-containing compounds 1 and 2, the 35 Cl NQR frequencies at 77 K are significantly lower than for the corresponding sulfur-containing analogs 3 and 4 (Table 1) [1, 2], which indicates higher electron densities on the Cl atoms in 1 and 2. This is explained by the fact that the sulfur atom is leas capable of p π -σ conjugation than the oxygen atom [2]. We hypothesize that such a ratio of the NQR frequencies and electron densities for these oxygen-and sulfur-containing compounds is because of polarization of the Z-Cl bonds due to the action of the charge on the S or O atom directly through the field, as in other compounds containing a nonlinear triatomic group Y-Z-M or Y-Z=M (see, for example, [3][4][5][6]). The negative charge on the oxygen atoms in molecules 1 and 2 should be significantly higher than on the sulfur atoms in molecules 3 and 4, which also should lead to the observed ratio of electron densities on the Cl atoms and the NQR frequencies for these compounds. Cl H H H H M(1) M(2) Z C(1) C(2) 1-4 1 Z = P, M(1) = M(2) = O; 2 Z = As, M(1) = M(2) = O; 3 Z = P, M(1) = M(2) = S; 4 Z = As, M(1) = M(2) = S