Gauging stability and reactivity of carbonyl O-oxide Criegee intermediates†
In this study, we evaluated the effect of substitution on the stability and reactivity of carbonyl O-oxide Criegee intermediates (CIs). In this regard, we computed a set of more than 50 carbonyl oxides at the CBS-QB3 level of theory and assessed their stability by means of an isodesmic reaction equation defining a carbonyl oxide stabilization energy (COSE). Almost all substituents are stabilizing and amino groups in particular leading to COSE values of almost 60 kcal mol−1. As opposed to π-donors, substituents with a strong σ-electron pull destabilize the CO–O group. Furthermore, we studied how the intrinsic stabilization of the Criegee intermediate is reflected in its CO and O–O bond lengths as well as the partial charges on the individual atoms of the carbonyl oxide moiety. As a potential measure for reactivity, we determined the adiabatic singlet–triplet energy gap of all carbonyl oxides. Amino substituted CIs exhibit high-lying triplet states and have relatively large barriers towards addition of water or the OH radical. However, the ΔES–T cannot serve as a rigorous measure for carbonyl oxide reactivity.