Reactions very often involve an electron donating
reagent that attacks a positive center. Moreover,
electrostatic interactions may determine the relative orientation of
two reacting species, and therefore the selectivity.
The distribution of charge can be expressed as an electrostatic potential map, showing the interaction a probe charge would experience from the nuclei and the electron cloud.
The calculation of atomic charges from the electron distribution is subject to discussion; i.e. the quality of the algorithms which assign the 'molecular' electrons to a particular atom (population analysis).