Transient resonance Raman investigation of 4-iminocyclohexa-2,5-dienylidene and 4-oxocyclohexa-2,5-dienylidene carbenes in aqueous solution

Abstract

We present transient resonance Raman spectra for the 4-iminocyclohexa-dienylidene and 4-oxocyclohexa-2,5-dienylidene carbene species in aqueous solutions. Comparison of the experimental vibrational frequencies to values computed from density functional theory calculations suggests that both carbenes are in their triplet states. Comparison of the structure and properties of the 4-iminocyclohexa-dienylidene to those previously found for several arylnitrenium ions indicates that the imine and cyclohexadienyl character of the 4-iminocyclohexa-2,5-dienylidene carbene is similar to the diphenylnitrenium ion. This suggests the smaller C-N bond order and lower cyclohexadienyl character of the triplet 4-iminocyclohexa-2,5-dienylidene carbene compared to the higher C=O bond order and greater cyclohexadienyl character of the triplet 4-oxocyclohexa-2,5-dienylidene carbene is mainly due to the charge delocalization ability of the second hydrogen atom in the -NH 2 + moiety. We briefly discuss the structure and properties of these two carbenes and their similarities and differences in chemical reactivity.