Nitrogen as a probable problematic factor of computational chemistry: A benchmarking study

In the present study, theoretical IR frequencies and geometric parameters of triamterene, furosemide, and triamterene-furosemide salt were investigated. ORCA software was handled for commonly used BLYP, B3LYP, and HF (combined with various basis sets including 6-31G**, def2-SVP, cc-pVDZ, and pcseg-1 basis sets) cal- culations. Theoretical IR frequencies and geometric parameters of triamterene and furosemide were compared with the corresponding experimental data. In addition, theoretical geometric parameters of triamterene- furosemide salt were, as well, compared with the corresponding experimental data. Based on these compari- sons, the performances of computational methods/basis sets were measured. As a result of this study, it was discovered that the studied computational approaches were generally successful in the prediction of molecular geometries and IR frequencies of the target molecules. When IR and geometry data were more deeply investi- gated, it was observed that there were problems specific to nitrogen atoms. The computed geometry and IR of amine and sulphonamide nitrogen atoms' bonds strongly disagreed with the experimental data. Similar dis- agreements were also observed for sulphur, oxygen, and cyclic hydrogen atoms but the level of disagreements was lower.

Automated summary

Theoretical IR frequencies and geometric parameters of triamterene, furosemide, and triamterene-furosemide salt were investigated using computational methods. The performances of the methods in predicting molecular geometries and IR frequencies were evaluated. Discrepancies between computed and experimental data were observed, especially for nitrogen atoms.