Thiosemicarbazones can exist in several tautomeric forms and conformations, with the possibility of intra- and intermolecular hydrogen bonding. Detailed structural characterization of thiosemicarbazones, as compounds that are associated with a wide spectrum of biological activities, is a prerequisite for better understanding of their bioactivity and for obtaining molecules with improved pharmacological properties. Solid and solution state multinuclear NMR spectroscopy (1H, 13C i 15N) was emloyed to explore the influence of the substituents, the nature of the solvent (different polarity and different proton-donor and proton-acceptor abbilities) and temperature on the molecular conformation, tautomerism and the nature of hydrogen bonding (intra- and intermolecular) of salicylaldehyde and 2-methoxybenzaldehyde thiosemicarbazone derivatives. The combination of known crystal structures and observed 13C and 15N chemical shifts in the solid state, was used as a basis for the detection of structural changes in solution. The experimental results were complemented with computational research of conformational space of selected compounds in a vacuum, and organic solvents (PCM approach), by combination of molecular- and quantum-mechanical methods. The most stable structures, obtained by molecular mechanics, were reoptimized in vacuum, CHCl3 and DMSO with B3LYP-D3/6-311++G(2df,2p) computational model. QTAIM population analysis method, together with Koch-Popelier criteria, was used for characterization of intramolecular hydrogen bonds in most stable conformers of investigated compounds.