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. W.
F. 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 [X C N]?. The relative
contribution of the hypothetical structure X=C=N? to the resonance hybrid
?X- C?N X=C=N? is higher in the case of X = O. The degree of the C?N or C N
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.