This chapter aims to summarize most of the previous findings using the optical basicity scale. First, the concepts of optical basicity and of ionic-covalent parameter are recalled and some examples given. Then, the choice of ionization potential as a means to account for a thermodn. selectivity is justified. The linear correlations obtained when plotting differences in ionization potential (DI) against the optical basicity are then discussed. Finally, the thermodn. nature of optical basicity is discussed and attempts to account for the linearity of correlations between DI and optical basicity are proposed
