Energetics and Structures of the Carbonyl Chloride Radical, Oxalyl Chloride, and Their Cations

Abstract

An ab initio study on the structures and energetics of the carbonyl chloride radical and its dimer, oxalyl chloride, along with their cations, was carried out using the Gaussian-2 (G2) and Gaussian-3 (G3) models of theory. The structural results obtained include optimized geometries of ClCO, ClCO+, the anti, syn, and gauche conformers of (ClCO)2 and the transition structure (TS) connecting the anti and gauche conformers, and (ClCO)2+. The energetic results reported include the heats of formation for ClCO, various (ClCO)2 conformers and transition structures, ClCO+, and (ClCO)2+, as well as the adiabatic and vertical ionization energies of ClCO and (ClCO)2. The G3 results obtained are in very good agreement with the available experimental data. In some cases, where the experimental data are unavailable or imprecise, the G3 results should be reliable estimates. Among the three experimental ΔHof298 values for ClCO found in the literature, the one most recently reported (−21.8 ± 2.5 kJ mol-1) has the best agreement with the G3 result (−19.4 kJ mol-1). For oxalyl chloride, we located a gauche conformer and a TS linking the anti and gauche conformers at the MP2(Full)/6-311+G(3df,2p) level, in qualitative agreement with the experimental findings. Also, both experimental and computational results agree that both the anti and gauche conformers lie in very flat potential minima. Based on the limited number of systems studied in this work, the G3 model yields results which are in better agreement with the experimental data than the G2 method.