Substituent effects on the stability of carbodiimides

Abstract

The geometries and energies of mono-substituted carbodiimides RNCNH and imines RNCH₂ have been obtained by ab initio DFT calculations. The geometries of carbodiimides with strongly electropositive substituents are linear, which is attributed to charge repulsion and a preference for sp-hybridization at the nitrogen atom. An isodesmic reaction was designed to study substituent effects on the stability of carbodiimides. The correlation between substituent group electronegativity χ_BE and the stability of carbodiimides was reasonably good. Electronegative substituents destabilize carbodiimides, whereas electropositive substituents stabilize them.