Spectroscopy, structure, thermal and photochemical decomposition of 5-chloro-3-trifluoromethyl-1,2,4-thiadiazole: Generation of trifluoroacetonitrile N-sulfide.

Abstract The structure and thermal and photochemical decomposition of the synthetic precursor 5-chloro-3-trifluoromethyl-1,2,4-thiadiazole (1) have been investigated for the first time by mid-infrared, Raman, ultraviolet and He I photoelectron spectroscopy. Spectroscopies, supported by quantum-chemical calculations using the B3LYP and SAC-CI methods, provided a detailed investigation into the vibrational and electronic character of the molecule. Thermal stability and photochemical decomposition of 1 have been studied in the gas phase and solid matrix, respectively. Flash vacuum thermolysis of the molecule produced fast quantitatively CF 3 CN, ClCN, and sulfur. However, UV irradiation of 1 in solid argon matrix at selected wavelengths of 213, 228, 240, and 250 nm resulted in a retro-cycloaddition reaction leading to the formation of a novel nitrile sulfide, CF 3 CNS (2), and ClCN. The structure of 2 was computed at the B3LYP and CCSD(T)/aug-cc-pVTZ levels, and its IR identification was supported by quantum chemical calculations. Graphical abstract Image 1 Highlights • 5-Chloro-3-trifluoromethyl-1,2,4-thiadiazole (1) was studied by spectroscopy. • Thermal decomposition of 1 was studied in the gas-phase. • Photochemical decomposition of 1 was investigated in solid argon matrix. • Trifluoroacetonitrile N -sulfide, CF 3 CNS (2), was generated and identified. • Structure of 1 and 2 were computed using quantum-chemical calculations. [ABSTRACT FROM AUTHOR]