π-Electronic Energy Levels of o-Benzoquinone

The π-electronic energy levels of o-benzo-quinone have been obtained by using Pople’s SCF MO method, while the electron repulsion integrals have been obtained by the Pariser-Parr method. The absorption band near 360 mμ and the strong band which is thought to exist near 200 mμ have unambiguously been assigned to the first 1A1→1B2 and the second 1A1→1A1 transitions respectively. The calculated singlet excited energy levels are much higher than the observed levels. The reason for this has been examined by SCF MO calculations using modified values of various kinds of electron repulsion integrals and core integrals. It has been concluded that a satisfactory lowering of the calculated singlet excited energy levels cannot be expected unless values of the core resonance integrals (β) are used which are much modified from those generally used. Simple MO parameters for o-benzoquinone adequate to simulate the simple MO’s to the SCF MO’s have been obtained.