Ab Initio Study of Bonding between Nucleophilic Species and the Nitroso Group

The bonding between anionic nucleophiles and the nitroso group has been studied in the common nitrosating agents nitroso chloride (ONCl), nitroso bromide (ONBr), nitroso thiocyanate (ONSCN), and dinitrogen trioxide (N2O3) in aqueous solution. A variety of theoretical methods were employed, including ab initio, density functional theory (DFT), and composite theoretical techniques, with solvent effects described using the polarizable continuum model (PCM). Experimental nitroso bond heterolytic dissociation free energies were accurately reproduced with a number of composite theoretical methods, the most successful being CBS-Q and G2MP2, with average errors of 3.1 and 3.4 kJ mol-1, respectively. Using the MP2 and B3LYP methods, calculations were made with correlation consistent basis sets up to quadruple-ζ, extrapolated to the complete basis set (CBS) limit. The MP2/CBS calculations were accurate to around 10 kJ mol-1, while the B3LYP/CBS calculations routinely overpredicted experimental bond free energies by...