PPP Molecular Orbital Calculations of Polyenyl Cations and their Analogs using New-γ and Pseudo Atom Modeling

The first absorption bands of the tetramethyl polyenyl cations were calculated by the Pariser-Parr-Pople molecular orbital method. By considering the extraordinary hyperconjugation effect of methyl substituents and using the new-y, the calculated absorption wavelengths reproduce well the observed ones.