Redox reaction thiol-disulfide for 3-, 4-and 6-methyl-5-nitopyridine derivatives - X-ray, electron absorption and emission, IR and Raman studies discussed in term of quantum chemical DFT calculations

Three new methyl-nitropyridine-thiols were synthesized and their reaction to disulfide forms were studied. All synthesized compounds were characterised by means of structural and spectroscopic measurements. The structures were confirmed by XRD and NMR studies as well as IR, Raman, UV-VIS, and emission spectra. The analysis of the obtained results was carried out using quantum chemical DFT calculations. The vibrational characteristics were reported and a full set of the normal modes typical of the thiol and disulfide groups were identified and assigned to respective IR and Raman bands. The results of structural and spectroscopic studies were used to find the dependence between the optical properties and position of the methyl group in studied pyridine derivatives. The calculated singlet and triplet states of the electron spectra were analysed to identify the unique spectral pattern resulting from the electrons of the C -S -S -C bond in the heterocyclic derivatives.