The role of reaction energy and transition state bond order on the reactivity of ambifunctional compounds in solution
Abstract
The ambident behaviour of some reagents, NO2–, SCN– and ambident bases, in liquid solutions can be accounted for, quantitatively, in terms of the intersecting-state model. For many reactions changes in reactivity are dominated by the reaction energy, ΔG°, and the transition state bond order, n‡. A gain in polarity of the reactive bonds during the course of reaction leads to more negative ΔG° and to a decrease in n‡. This reveals that for the reaction energy barrier, ΔG° and n‡ can work in opposite directions as a function of the electronegativity of the reaction sites and be responsible for ambident behaviour in ‘charge control’ reactions (ΔG°) and ‘frontier-orbital control’ reactions (n‡). These concepts are employed to interpret the role of reagent, solvent, cation, and reaction mechanism on ambident reactivity.