Aromaticity of an Unsaturated N-Heterocyclic Stannylene (HCRN)2SnII As Studied by Optical Spectra and Quantum Chemistry. Comparison in the Series (HCRN)2EII, E = C, Si, Ge, Sn (R = t-Bu or Dip)

The degree of pi-electron delocalization in a series of unsaturated N-heterocyclic compounds containing divalent group-14 atoms, (HCRN)(2)E-II (E = C, Si, Ge, Sn), has been estimated by applying different experimental and theoretical criteria (vibrational and UV-vis spectroscopy, nucleus-independent chemical shifts, and isomerization stabilization energies). All of the methods used confirmed the aromaticity of these heterocyclic molecules involving Six pi electrons, and most of the Methods indicated that the aromaticity increases in going from the silylene to the stannylene.