| Abstract: | Using the Hartree-Fock, MP2, and the B3LYP, BLYP, mPW1PW91 density functional methods, each combined with the 6-31G(d), 6-311G(d), 6-311+(d), 6-311++G(d, p) cc-pvdz and cc-pvtz basis sets, the equilibrium geometry of 4,4′ -bipyridine was optimized and the internal rotational potential barriers heights at 0° (AE0), 90° (AE90) were obtained. For the best basis set (cc-pvtz) , the predicted dihedral angle e ranges from 37.0 to 37.8° for all methods except the Hartree-Fock method (43.7). This agreed with the estimation from the electron diffraction experimental measurement (37.2°). The inter-ring C-C distance, ranging from 147.2 to 148.7 pm ( 147 pm experimental), is intermediate between the typical aromatic C-C bond and the aliphatic C-C bond. The results show that the inter-ring o-conjugation between two pyridyl rings stabilizes the co-planar conformer and the steric repulsion between the ortho neighboring hydrogens belonging to different rings favors the non-planar orthogonal conformer. |
