Notiz über die Berechnung des längstwelligen π‐π‐Überganges nach dem Verfahren von E. H ÜCKEL

The transition energies for the long‐wave absorption bands of aromatic and unsaturated systems, as calculated by the simplest one‐electron approximation, are corrected by a first‐order perturbation procedure for the charge drifts and bond order alterations due to the promotion of an electron from the upper bonding to the lowest anti‐bonding molecular orbital. A significant improvement in the correlation of observed vs . calculated transition energies is obtained. The important factor is the correction for compression energies, rather than the correction for charge drifts.