A theoretical study of the conformation of 2,2'-bifuran, 2,2'-bithiophene, 2,2'-bitellurophene and mixed derivatives: Chalcogen-chalcogen interactions or dipole-dipole effects?

Using as models 2,2′-biheterocycles (furan, thiophene, selenophene, tellurophene) the possibility of stabilizing effects due to the proximity of two chalcogen atoms (O, S, Se, Te) was explored. The geometries of the ground states were compared satisfactorily with the available experimental results. The torsional barriers through planar and orthogonal transition states were calculated and discussed in function of the nature of the chalcogen atoms. Special attention was devoted to dipole moments that were calculated by a vector summation with good results.