Carbonyl Oxides: Zwitterions or Diradicals?

Abstract

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 n o 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 UVjVIS 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 a b initio calculations carbonyl oxides are best viewed as polar diradicals. The zwitterionic state lies at higher energies and should be stabilized by R donors.

The oleic acid-ozone heterogeneous reaction system: products, kinetics, secondary chemistry, and atmospheric implications of a model system – a review

“…diradicals) in the literature on the heterogeneous ozonolysis of OL. The discord in this description has its roots in part in the debate on the electronic structure of these intermediates that are extant in the organic chemistry literature (Bunnelle, 1991;Harding and Goddard III, 1978;Sander, 1990). Criegee showed that for ozonolysis in solutions there was evidence indicating CI were zwitterionic (Criegee, 1975) based on reactivity trends (Criegee, 1975;Criegee and Wenner, 1949).…”

“…In this section we will present a concise summary of the established reactivity of CI for these cases and in the following sections provide discussion that the CI react more in accord with solution chemistry. We will not present any details regarding a third experimental regime, namely investigations of CI in inert matrices under cryogenic conditions but interested readers can find several reviews (Bunnelle, 1991;Sander, 1990) that cover this topic of extensive research.…”

Perspective: Spectroscopy and kinetics of small gaseous Criegee intermediates

“…1 The important roles of reactive species of this type, commonly known as Criegee intermediates, are generally accepted in ozonolysis reactions in organic chemistry and atmospheric chemistry, [2][3][4][5][6][7] even though these intermediates have not been detected directly in the gaseous phase until recently. The reactions of ozone with alkenes are important in the atmosphere because they are responsible for the non-photolytic production of OH, an important oxidizing and cleansing agent in the atmosphere, especially under conditions of dim light such as during winter and at night.…”

Dimetildioxirano. 1. Oxidação de compostos de enxofre

“…Os exemplos 7 e 8 indicam que óxidos carbonílicos, gerados in situ por fotooxigenação dos correspondentes diazoalcanos [10][11][12] , são oxidantes nucleofílicos. Os exemplos 9-10 e 11-12 apenas confirmam que oxidantes nucleofílicos apresentam X SO próximo de 1,0, e para oxidantes eletrofílicos X SO próximo de zero, respectivamente.…”

“…Cálculos teóricos [5][6][7][8][9] e dados espectroscópicos [10][11][12][13][14][15] estabeleceram inequivocadamente que dioxiranos 1 e óxidos carbonílicos 2 são espécies isoméricas separadas por uma elevada barreira energética. Bach e colaboradores 6,7 , através de cálculos ab initio, encontraram para a interconversão do dioxirano 1a (R 1 = R 2 = H) no respectivo óxido carbonílico 2a uma barreira energética na faixa de 29,7 a 54,1 kcal.mol -1 .…”