Ring currents as probes of the aromaticity of inorganic monocycles:P_5~-,As_5~-,S_2N_2,S_3N_3~-,S_4N_3~+,S_4N_4~(2+),S_5N_5~+,S_4~(2+) and Se_4~(2+)

摘要

Current-density maps were calculated by the ipsocentric CTOCD-DZ/6-311G (CTOCD-DZ=continuous transformation of origin of current density-diamagnetic zero) approach for three sets of inorganic monocycles:S_4~(2+),Se_4~(2+),S_2N_2,P_5~- and As_5~- with 6 pi electrons;S_3N_3~-,S_4N_3~+ and S_4N_4~(2+) with 10 pi electrons;and S_5N_5~+ with 14 pi electrons.Ipsocentric orbital analysis was used to partition the currents into contributions from small groups of active electrons and to interpret the contributions in terms of symmetry-and energy-based selection rules.All nine systems were found to support didatropic pi currents,reinforced by sigma circulations in P_5~-,As_5~-,S_3N_3~-,S_4N_3~+,S_4N_4~(2+) and S_5N_5~+,but opposed by them in S_4~(2+),Se_4~(2+) and S_2N_2.The opposition of pi and sigma effects in the fourmembered rings is compatible with height profiles of calculated NICS (nucleus-independent chemical shifts).