A computational study of the conformational stability, vibrational spectra, and thermochemical properties of 2,6-dichlorobenzamide, 2-(trifluoromethyl)benzamide, 2-(trifluoromethyl)benzoic acid, and 3-chloro-5-(trifluoromethyl)pyridine-2-carboxylic acid

Abstract

2,6-Dichlorobenzamide (BAM), 2-(trifluoromethyl)benzamide (TBAM), 2-(trifluoromethyl)benzoic acid (TBA), and 3-chloro-5-(trifluoromethyl)pyridine-2-carboxylic acid (PCA) are degradation by-products of fluopicolide and fluopyram fungicides. In this work, a detailed theoretical study of their different molecular, spectroscopic and thermochemical properties was carried out with different formulations of the density functional theory and high-level model chemistries. The mean values of -146.0 ± 6.3, -763.2 ± 6.3, -949.0 ± 6.3, and -919.4 ± 6.3 kJ mol-1 for the standard enthalpies of formation of BAM, TBAM, TBA and PCA, respectively, were derived for the first time at the G3MP2//DFT and G4MP2//DFT levels of theory (DFT = B3LYP, BMK, and B98). Additionally, a good agreement between formation enthalpies derived from isodesmic reaction approach and from Benson's group additivity method was obtained.