The selected derivatives of the 2-and 3-benzo [b]furancarboxylic acids were synthesized and their structures were studied using the X-ray crystallography and the computational methods. The monocarboxylic acids (1-3) crystallize as dimers stabilized by the O-HÁÁÁO intermolecular hydrogen bonds. Moreover, intramolecular hydrogen bonds are formed between the OH and C(=O)CH 3 groups, substituted to the aromatic ring (2-4). In the crystal structures of 1-4, weak C-HÁÁÁO, C-HÁÁÁp, and C-HÁÁÁBr interactions stabilize the three-dimensional packing of molecules. The crystalline sodium complex of 1 has the stoichiometry [Na 1 Á1A 2 Á1B]Á1C, thus, the asymmetric unit contains three different moieties of 1. In this complex, the Na ? cation is hexacoordinated having a strongly distorted tetragonal bipyramidal polyhedron. For each molecule 1-4, several conformers were obtained in the gas phase. It was achieved by the rotations of substituents [COOR and/or C(=O)CH 3 , where R = H, CH 3 ] with respect to the rigid benzo[b]furan system. As indicated by the quantum-chemical calculations, the solid-state conformers for 3 and 4 (3-benzo[b]furancarboxylic acid derivatives) are the most stable ones. In contrast, the solidstate conformers of the 2-benzo[b]furancarboxylic acid derivatives (1, 2) have the energies higher than the lowest energy conformer by 1.23 and 0.69 kcal/mol, respectively. It seems that intermolecular contacts in the crystal influence on the orientation of substituents, and the conformers observed in the sodium complex of 1 provide evidence of such flexibility.