The π-Electron distribution in Pyridine and the molecular-orbital parameters for nitrogen

Abstract

The π-electron distribution in pyridine has been calculated by the self-consistent-field molecular-orbital method, including electron interaction explicitly. Empirical parameters analogous to the coulomb parameters in the simple molecular-orbital theory are not required in the calculations. The results have been compared with chemical properties of pyridine and have also been used to determine the most suitable values for the coulomb parameters in the simple molecular-orbital treatment of pyridine. It emerges that, in addition to a coulomb parameter to allow for the eleotronegativity of nitrogen being greater than that of carbon, an appreciable auxiliary coulomb parameter, representing an enhanced electronegativity of carbon atoms adjacent to the hetero-atom, must be introduced. This auxiliary parameter is necessary to allow for purely π-electron effects in the vicinity of a hetero-atom and is additional to any parameter which might be required owing to σ-electron polarization effects around the nitrogen atom.