THEORETICAL STUDIES ON THE ELECTRONIC SPECTRA OF SUBSTITUTED AROMATIC MOLECULES: PART II. SEMIEMPIRICAL SELF-CONSISTENT FIELD CALCULATIONS ON ANILINE

Abstract

The results of 14 calculations on the aniline molecule using different choices of parameters within the framework of the semiempirical SCFMO method have been carried out using an automatic Fortran 1A program written for an I.B.M. 1620 computer. It has been shown that the approximation of using the valence state ionization potential as a measure of the core integral of a heteroatomic substituent underestimates the amount of electron transfer between substituent AO and the benzene MO's. By adjusting this core integral empirically or by using a variable electronegativity MO approach it has been found possible to obtain, for the same set of parameters, agreement between experiment and theory for: the first two electronic transitions in the vapor state (4.23–4.38 ev and 5.22–5.41 ev), the change in ionization potential relative to benzene (AI = 1.54 ev), and the electron density para to the amino group (ρ₄^π = 1.059). It was not found possible to calculate values for the π-electron dipole moment and oscillator strengths which agreed, for any reasonable choice of parameters, with experimental values.