Ligands of low electronegativity in the VSEPR model: Molecular pseudohalides

Abstract Equilibrium structures and force constants at linearity, for the skeletal bending mode δ (RNX) have been calculated in the MNDO approximation for 67 isocyanates, isothiocyanates and azides, RNXY (XY = CO, CS or N 2 ) and the corresponding structures and force constants, δ (RCN), for 12 fulminates RCNO. Fulminates all have linear skeletons, but for RNXY the molecular skeleton is linear at atom X only if it is linear at N also; otherwise the skeleton RNXY has a trans planar structure. Bending force constants are large and negative for all azides studied, negative for methyl and substituted methyl isocyanates and isothiocyanates and very small and positive for silyl and substituted silyl isothiocyanates: for silyl and substituted silyl isocyanates, the force constant is small and positive when the R group has effective C 3v symmetry, but small and negative when the R group has only effective C s symmetry.