Are the Structural Analogues and Charged Homologues of Carbones Pseudoallenes (R2C=C=CR2), Pseudocarbenes (R2C-C:-=C+R2) or Pseudocarbones (R2C+-C2--C+R2)? An Answer Given on the Magnetic Criterion.

Abstract

Carbones bear the same resonance contributor X⁺-C^2--Y⁺ (X⁺, Y⁺ = PR₃ ⁺, CR₂ ⁺, SR₂ ⁺, SeR₂ ⁺, S⁺R₂ = NR) and exhibit unique bonding and donating properties at the central carbon atom. Both the analogues of carbones C⁺-Z^2--C⁺ (Z = Si, Ge, Sn, Pb) and the large number of charged main group homologues C=Z=C (Z = B^-, Al^-, Ga^-, N⁺, P⁺, As⁺, Sb⁺, Bi⁺, O²⁺, S²⁺, Se²⁺ and Te²⁺) are known for comparable bonding and donating properties. The electronic structure of the carbone homologues and analogues has been studied on basis of both their geometry and their spatial magnetic properties (through-space-NMR-shieldings [TSNMRSs]) with regard to the present dominating electronic structure (beside carbone-like [⁺C-Z^2--C⁺] also allene-like [C=Z=C] or carbene-like [⁺C-Z^-=C]). TSNMRS values have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The synergy of geometry (bond lengths, bond angles of linear, bent, orthogonal or twisted structures) and the spatial magnetic properties (anisotropy effect of C=C in allene-like or partial C=C double bonds in carbene-like structures, and the ball-like anisotropy effect of central hetero atom Z of carbone-like structures) provide a comprehensive picture of the respective structure and the dominating resonance contributor.