Semiempirical Calculation on the Electronic Structure of the Nitrogen-Containing Heterocyclic Molecules. IV. Electronic Structure of Pyridine

Publisher Website
Google Scholar
Abstract
The semiempirical theory on the electronic structure of the nitrogen heterocycles, proposed in Part I of this series, is applied to pyridine. Only the singlet levels are considered in this paper, deferring the discussions on the triplet levels to a later publication. Doubly excited as well as singly excited configurations are taken into CI calculation. The hybridization parameter λ of the nitrogen nonbonding AO determined so that the calculated value of the lowest singlet‐singlet n—π transition energy agrees with the experimental value is +0.5439 which corresponds to 22% s character of the nitrogen nonbonding AO. By assuming this value of λ, the lower singlet levels of this molecule are calculated and compared with experiment. The calculation shows that a hidden n—π transition (1A2—1A1 transition) exists in the neighborhood of the strong 4.8‐ev band which is assigned to a π—π transition.