ABSTRACT
Numerous activities and properties of organic molecules only depend on the presence of specific atoms and/or functional groups in their structure. These features can be used for deriving QSAR and QSPR models via regression analyses or artificial neural networks. Other activities can be directly related with physicochemical properties easily interpretable such as the 1-octanol/water partition coefficient. Last, numerous valuable QSAR and QSPR models have been derived from topological indices. The aim of this chapter is to stress some advantages and limitations of these different types of parameters in order to show that the universal molecular descriptor does not exist.
