Stabilisation of Charged Species
This chapter introduces the two main forms of charge stabilisation in the context of polarised bonds, that is, the inductive and mesomeric effects. However, for most reactions it is the effects of inductive and mesomeric groups that have most influence upon the stability of the charged species. The simplest, commonly encountered, charged hydrocarbon species is the methyl cation. The mesomeric effect operates through the n bond system. The state that occurs mid-way along the bond-breaking/bond-forming route is called the transition state, and represents a species that is very short lived. In all transition states, the distribution of charge is different from that found in the original molecules. In order to facilitate the reaction, the charges that have been created by the reagents within the transition state may be stabilised. The inductive effect results from the difference in the electronegativities of the atoms under consideration.