ABSTRACT
In density functional theory (DFT), electron density is the key quantity determining the properties of a molecular system. Electron density is always positive and its value constitutes a fundamental descriptor. However, chemical reactivity of a molecule cannot be described by its electron density alone, because the course of a reaction is rather determined by its response toward different perturbations caused by an approaching reagent. Sensitivities of an electron density toward structural modifications and its responses to changes in external potential and conditions are actually more important in reflecting the reactivity of the corresponding system, than its absolute values. Several global and local reactivity indices have thus been derived within the framework of DFT that are basically the measures of molecular system’s responses. As discussed in various chapters of this book, these global and local reactivity indices, such as chemical potential (m), hardness (h), and Fukui function, are defined as the first or second derivative of electronic energy and electron density.
The global parameters help understanding the behavior of a system and lead to applicable and useful principles such as the principle of maximum hardness (MHP) [1]. In this chapter, however, our main focus is to introduce the working formula of local reactivity parameters, their actual computations, and practical ways of application to different types of organic reactions. In this process, we mention briefly some of the relevant global reactivity parameters and their calculations as well just to have continuity in the subject matter.
