The Molecular and Electronic Structures of Carbodiimides

Abstract

The electronic absorption spectra of N, N'-diphenylcarbodiimide (DPC) and N-methyl-N'phenylcarbodiimide (MPC) were measured in cyclohexane and ethanol, and MINDO/2 calculations were performed for these compounds. It has been clarified that the structure of DPC is linear with the two benzene rings orthogonal to each other. The polarized absorption spectra of DPC and MPC were measured by means of a stretched polymer film technique, and the polarization of each electronic transition was determined. From the above experimental results together with PPP calculations extended to the 3-dimensional system, the nature of each electronic transition was clarified. The 284 nm and 202 nm electronic bands of DPC are polarized along the short molecular axis. The former band is interpreted as an intramolecular charge transfer transition from the N=C=N group to the phenyl groups, and the latter as the back charge transfer one.