Organic chemistry represents an extensive volume of facts from which the contemporary doctrine of reactivity is built. The most important basis of this doctrine is the idea of intermediate species that arise along the way from the starting material to the nal product. Depending on the nature of chemical transformation, cations, anions, and radicals are created midway. These species are formed mainly as a result of bond rupture. Bond rupture may proceed heterolytically or homolytically: R-X → R− + X+, R-X → R+ + X−, or R-X → R• + X•.