Ipsocentric approach

The few-electron character of ring currents uncovered by the ipsocentric approach prompts many questions about the links between aromaticity/strobilism and distortivity. Just two examples from recent work [14] will be discussed briefly here. 

Fig. 5. Computed map of the 77 current density calculated in the ipsocentric approach for pentalene optimised at the RHF/6-31G level [14c]. Arrows show the projection of the current density induced by unit perpendicular magnetic field in the plane 1 bohr above the molecule. The clockwise sense indicates paramagnetic (anti-Lenz) circulation.

Optimization at the restricted Hartree-Fock (RHF) and DFT (B3LYP) levels in the 6-31G basis set has also contributed to structural clarification of [l,2,5]thiadiazolo[3,4-f][l,2,5]thiadiazole 6 both approaches successfully predict that 6 ought to have planar equilibrium geometry. Direct a3 initio ipsocentric calculations of the total 7t-current density map for 6 permits classification as aromatic according to magnetic criteria. It exhibits a strong and uniform diatropic perimeter circulation, of comparable intensity to the parent monocycle 11 and similar to that of naphthalene <2004JA11202>. 

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