Ab Initio Study of Nitromethane Deprotonation by (OH)-·nH2O Clusters

The deprotonation of nitromethane by (OH) - · n H 2 O clusters has been studied. Ab initio quantum chemistry calculations including electron correlation are used to determine the geometries, energetics, and natural bond orbital electronic populations of reactants, transition states, and products for the cases of n = 0 and n = 2. An analysis of the negative charge redistribution during the reactions is given. In particular, special attention is devoted to the evolution of the negative charge on carbon, which has been implicated in the past in the observed anomalous values of the Brønsted parameter in the reaction of interest, the so-called “nitroalkane anomaly”. Finally, the deprotonation of nitromethane by (OH) - is compared with the analogous reaction involving acetonitrile; the results suggest that the high electron affinity of the NO 2 group is critical for the existence of the nitroalkane anomaly.