THE VARIETY OF MOLECULAR SCHEMES AT THE BORDER BETWEEN POLAR AND ET MECHANISMS

Experiments exploring the mechanisms operating at the border between polar and ET mechanisms are described. Starting from a given donor-acceptor (D-A) couple the following mechanistic possibilities are examined on appropriate systems: in-cage versus out-of-cage reactivity, hidden ambident reactivity, pre-equilibria (ion pairing, clustering etc.) where one type of subspecies reacts by ET and another type by polar mechanisms, observations hinting deceptively at the coexistence of ET and a polar pathway, for a given D-A couple, transitions states of varying looseness. The proposed coexistence of ET and polar pathways in a given D-A system is therefore far more often a starting point for further mechanistic investigation than a mechanistic conclusion.