Computational and experimental studies on the IR spectra and structure of the simplest nitriles (C1 and C2), their anions, and radicals

The structure and infrared spectra of formonitrile (hydrogen cyanide) and acetonitrile, their anions, and radicals (45 species in all) have been studied by density functional theory (DFT) B3LYP 6‐31++G(d,p) calculations. The results obtained have been compared with the literature and original experimental data. The zero‐point vibrational energy (ZPVE)‐corrected deprotonation energies of the studied (and other) nitriles correlate fairly well (R = 0.94) with their pKa values, measured in dimethyl sulfoxide (DMSO). The theoretical cyano stretching frequencies νCN of the species studied have been found to correlate satisfactorily (R = 0.97) with the experimental ones. The latter correlation can be used for a theoretical estimation of νCN of many nitriles, their anions, and radicals. The geometry parameters for the molecules, calculated by the same theoretical method, practically coincide with those determined experimentally in the gas state.