ABSTRACT:Ab initio methods at the levels HF/cc-pVDZ, HF/6-31G(d,p), MP2/ccpVDZ, and MP2/6-31G(d,p), as well as methods based on density functional theory (DFT) employing the hybrid functional B3LYP with the basis sets cc-pVDZ and 6-31G(d,p), have been applied to study the conformers of 2,6-distyrylpyridine. Bond distances, bond angles, and dihedral angles have been calculated at the B3LYP level.The calculated values were in good agreement with those measured by X-ray diffraction analysis of 2,6-distyrylpyridine. The values calculated using the Hartree-Fock method and second-order perturbation theory (MP2) were inconsistent. The optimized lowestenergy geometries were calculated from the reported X-ray structural data by the B3LYP/cc-pVDZ method. Three conformations, A, B, and C, were proposed for 2,6-distyrylpyridine. Calculations at the three levels of theory indicated that conformation A was the most stable structure, with conformations C and B being higher in energy by 1.10 and 2.57 kcal/mol, respectively, using the same method and basis function. The same trend in the relative energies of the three possible conformations was observed at the two levels of theory and with the different basis sets employed. The reported X-ray data were utilized to optimize total molecular energy of conformation A at the different calculation levels. The bond lengths, bond angles, and dihedral angles were then obtained from the optimized geometries by ab initio methods and by applying DFT using the two basis functions cc-pVDZ and 6-31G (d,p). The values were analyzed and compared. The calculated total energies, the relative energies of the molecular orbitals, the gap between them, and the dipole moment for each conformational structure proposed for 2,6-distyrylpyridine are also reported.