CARBONYL OXIDES - ZWITTERIONS OR DIRADICALS

Over the last few years new experimental and theoretical methods have made it possible to gain a more detailed insight into the chemistry of short‐lived reaction intermediates. In 1949 Criegee postulated the intermediacy of carbonyl oxides in the mechanism of ozonolysis, and since then these species have become the goal of much research effort. Even though the formation of “Criegee zwitterions” during ozonolysis and carbene oxidations was proven by scavenger experiments, the electronic structure—zwitterion or diradical—of this short‐lived species is still a subject of debate. To date no stable carbonyl oxide has been found to exist under “normal” laboratory conditions, although by using matrix isolation and laser spectroscopy, it has been possible to obtain highly resolved IR and UV/VIS spectra of carbonyl oxides as well as to determine their dipole moments experimentally. The influence of substituents, exact kinetic data on modes of formation, and the subsequent reactions of carbonyl oxides as well as their photochemistry complete the picture. In accordance with ab initio calculations carbonyl oxides, are best viewed as polar diradicals. The zwitterionic state lies at higher energies and should be stabilized by π donors. Copyright © 1990 by VCH Verlagsgesellschaft mbH, Germany