The cyanide, cyanate, thiocyanate ambident anions: Structure, topological analysis of electron density and homolytic oxidative coupling regioselectivity

At the B3LYP/6-311++G(3df,3pd) level of theory, the spatial and electronic structure of the cyanide, cyanate and thiocyanate ambident anions has been studied. By means of the natural bond orbital (NBO) analysis and the R. F. W. Bader's quantum theory "Atoms in Molecules" (QTAIM), the electron density delocalization and topological properties in the above anions have been investigated. The distribution of electron density (NBO, QTAIM) in the XCN- (X = O, S) anions is reflected by the scheme . The relative contribution of the hypothetical structure X=C=N- to the resonance hybrid X--C equivalent to N <-> X=C=N- is higher in the case of X = O. The degree of the C equivalent to N or bond triple character and bond strength changes in the following series of anions: CN- > SCN- > OCN-. The occupancy of the lone electron pair (LP) orbital of the nitrogen atom in the above anions is close to 2, and the LP orbital is sp-hybridized. Condensed K. Fukui functions for the electrophilic attack have been evaluated. Local hardness of the donor reaction centres: N > C (CN-), O > N (OCN-), N > S (SCN-). The regioselectivity of the homolytic oxidative coupling reactions of the CN-, OCN-, SCN- anions has been substantiated.