Knowledge Bank

The orbital valency force field with inclusion of van der Waals repulsion terms has been applied to allene, ketene and diazomethane, and the application of this field to ethylene has been re-examined. Correlations among these molecules is generally very good. The van der Waals repulsion are adequate to account for the off-diagonal F matrix elements except in the case of diazomethane. The frequencies for $CH2N2$ and $CD2N2$ can be explained only if some negative off-diagonal elements are employed and this appears to be a result of a direct attraction between the hydrogens and the terminal nitrogen of the molecule.