The unusual neutral OCOCO and possible charged analogues. A theoretical investigation

Abstract

Calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31+G(d) level of theory indicate that singlet neutral OCOCO is unstable with respect to dissociation to CO2 and CO. In contrast, triplet OCOCO is a stable species provided it can be formed with excess energy of less than 41 kJ mol-1 [the process 3OCOCO → 1CO + 3CO2 is endothermic by only 9 kJ mol-1, but the barrier for this process is 41 kJ mol-1]. Triplet OCOCO is not accessible by one-electron oxidation from [OCOCO]-&z.rad; or one-electron reduction from [OCOCO]+&z.rad; because neither of these charged species is stable at the level of theory used for these calculations. A report by Cooper and Compton indicates that dissociative electron capture by maleic anhydride results in loss of the elements of C2H2 yielding an anion C2O3−&z.rad;. Calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31+G(d) level of theory suggests that the ion radical C2O3−&z.rad; may be the stable species [O2C-CO]−&z.rad; provided that the dissociating maleic anhydride radical anion has excess energy of at least 260 kJ mol-1. © 2001 The Royal Society of Chemistry.