On the Calculation of Electronic Levels in Pyridine and the Isomeric Picolines

The molecular orbital method was used for calculating electronic levels in pyridine and the picolines. The change of the benzene Coulomb integrals caused by the nitrogen atom in the ring and the CH3 substitution is treated by introducing into the secular determinant perturbation parameters δk at the appropriate positions. Bonding and antibonding single-electron molecular orbitals are calculated neglecting the overlap integral and electronic repulsion. The average heights are determined for the four one-electron transitions corresponding to the fourfold degenerate level in benzene. By using the assumption that the centers of gravity of the actual singlets are proportional to these average heights, these centers of gravity are predicted for pyridine and the three picolines using two different perturbation parameters δN. The values for pyridine show satisfactory agreement with the experimental mean value 6.14 ev.