Calculation of the infrared spectra of organophosphorus compounds and prediction of new types of nerve agents

Abstract

Currently, the available spectroscopic data on Novichok candidates are limited because experimental measurements are difficult to conduct due to the toxicity of these candidates. Furthermore, the Chemical Weapons Convention (CWC) revealed the main skeleton of the Novichok candidates, which contains thousands of possible structures. Therefore, to accurately predict the IR spectra of Novichok candidates, experiments and density functional theory (DFT) calculations with additional calibration were successfully performed in this study. Optimal calculation and scaling methods were derived by comparing the experimental and calculated values of five organophosphorus (OP) compounds. Furthermore, to establish a more accurate DFT calculation method for the IR spectrum prediction of Novichok candidates, five G-and V-type nerve agents were compared. By applying the derived B3LYP (scaled) method, the IR spectra calculations were performed for A-230, A-232, and A-234 agents, and the wavenumbers of the major functional groups appearing in the spectra were identified. It was found that P–O–C stretching and C–H bending vibrations are characteristic of all three agents. Moreover, the calculation results for an additional 83 Novichok candidates are presented for use in future identification methods. These results suggest an indicator for the classification and IR characteristics of Novichok candidates in the future. In addition, it can contribute to developing a large database of IR spectra by applying the optimal calculation method to new types of nerve agents.