Electronic structure, aromaticity, and physicochemical characteristics of carbene, radical, and ionic forms of compounds of the imidazole series, and their oxo and thio analogs

The effects of benzannellation, phenyl substitution at the nitrogen atom, protonation at the carbene carbon, ionization, and the state of the carbene center (σ² or π²) on the electronic structure, diamagnetic susceptibility, induced π-electron ring currents, the ¹H, ¹³C, and ¹⁴N chemical shifts, and the energies of the lowest electronic transitions of imidazol-2-ylidenes and their oxo and thio analogs were examined in the bound version of π-electron perturbation theory. The calculated and experimental data are compared.