New Bis-1,3,4-Thiadiazoles Based on Fumaric Acid: Preparation, Structure Elucidation, Antibacterial Activities, and Quantum-Chemical Studies

New bis-1,3,4-thiadiazoles 1–7 were obtained by the reaction of fumaric acid and N-(alkyl/aryl/cyclic)thiosemicarbazides in presence phosphorous oxychloride. The structures all compounds elucidated FT-IR, 1H NMR, 13C NMR elemental analysis. Antibacterial activity was studied for eight selected bacteria. Compounds 2–7 exhibited effect on Klebsiella pneumoniae. However, none Pseudomonas aeruginosa, Staphylococcus epidermidis, Salmonella enterica serovar Kentucky, Serratia marcescens. Self-consistent force (SCRF) calculations performed DMSO medium to examine solvent energies using CPCM SMD models. 6-31G(d) 6-311++G(2d,2p) basis sets used DFT calculations. Besides electronic parameters such as electronegativity, electrophilicity spectroscopic examinations compounds, QTAIM, local electron affinities, Fukui analyses also performed. Theoretical approaches supporting experimental observations revealed that containing aromatic cyclic groups exhibit stronger antibacterial behavior than aliphatic groups.