Simulant Molecules with Trivalent or Pentavalent Phosphorus Atoms: Bond Dissociation Energies and Other Thermodynamic and Structural Properties from Quantum Chemical Models

Abstract

The CBS-QB3 and G4 thermochemical models have been used to generate energetic, structural, and spectroscopic data on a set of molecules with trivalent or pentavalent phosphorus atoms that can serve as simulants of chemical warfare agents. Based on structural data, the conformational stabilities of these molecules are explained in terms of the anomeric interaction within the OPOC and OPSC fragments. For those cases where experimental data are available, comparisons have been made between calculated and previously reported vibrational frequencies. All varieties of bond dissociation energies have been examined except those for C-H and P═O bonds. In trivalent phosphorus molecules, the O-C and S-C bonds have the lowest dissociation energies. In the pentavalent phosphorus set, the S-C bonds, followed by P-S bonds, have the lowest dissociation energies. In the fluorinated simulant molecules, the P-F bond is strongest, and the P-C or O-C bonds are weakest.

Quantum chemical calculation of the structure, dipole moment, and polarizability of O-methyl methylphosphonofluoridate in the gas phase

“…1). This is consistent with the results of the most reliable previous calculations by CBS-QB3 and G4 methods [6].…”

“…The same range contains the values calculated by the MP2full method with quite large Dunning cc-pVTZ, aug-cc-pVTZ, and cc-pVQZ basis sets: 11.8 kJ/mol, 11.4 kJ/mol, and 12.0 kJ/mol respectively. The found values are consistent with the results of the calculation by the CBS-QB3 method (11.8 kJ/mol) [6]. Assuming the approximate equality to the mentioned ΔE values of the relative Gibbs energy, the calculation results in the 99:1 ratio for conformers 1 and 2 in the equilibrium mixture at 25 °С.…”

“…It is essential that conformer 1 and the most stable conformers of IMPF [11], O-ethyl methylphosphonofluoridate [6], and PMPF [12,13] have not only similar geometric parameters related to the phosphorus atom environment, but also similar values of the torsion angles corresponding to the rotation about the PO1 bond. Thus, the distinctions in the ϕ FPO1C1 , ϕ O2PO1C1 , and ϕ C2PO1C1 angles that we calculated for conformer 1 from those of the three most stable IMPF conformers calculated by the B3LYP/6-311++G(2d,2p) and MP2/6-311++G(2d,2p) methods [11] do not exceed 8.5° and 10.5° respectively.…”

“…The energies were calculated by the B3LYP/6-311G(2df,p)//B3LYP/6-31G(d) method. In the recent work [6], the energies have been found by more reliable composite CBS-QB3 and G4 methods. As in the majority of the previous calculations [2][3][4][5], two stable conformers were found [6].…”

“…In the recent work [6], the energies have been found by more reliable composite CBS-QB3 and G4 methods. As in the majority of the previous calculations [2][3][4][5], two stable conformers were found [6]. However, the geometric parameters (which were not presented) were calculated by not so reliable DFT(B3LYP) method with not large 6-311G(2d,d,p) [CBS-QB3] and 6-31G(2df,p) [G4] basis sets.…”