Visualization of electron density changes along chemical reaction pathways

We propose a simple procedure for visualising the electron density changes (EDC) during a chemical reaction, which is based on a mapping of rectangular grid points for a stationary structure into (distorted) positions around atoms of another stationary structure. Specifically, during a small step along the minimum energy pathway (MEP), the displacement of each grid point is obtained as a linear combination of the motion of all atoms, with the contribution from each atom scaled by the corresponding Hirshfeld weight. For several reactions (identity S(N)2, Claisen rearrangement, Diels-Alder reaction, [3+2] cycloaddition, and phenylethyl mercaptan attack on pericosine A), our EDC plots showed an expected reduction of electron densities around severed bonds (or those with the bond-order lowered), with the opposite observed for newly-formed or enhanced chemical bonds. The EDC plots were also shown for copper triflate catalyzed N2O fragmentation, where the N-O bond weakening initially occurred on a singlet surface, but continued on a triplet surface after reaching the minimum-energy crossing point (MECP) between the two potential energy surfaces. [GRAPHICS] .

Automated summary

We propose a simple procedure for visualizing electron density changes during chemical reactions. By mapping grid points from a stationary structure to distorted positions around atoms of another stationary structure, we can observe the variations in electron density during bond formation and cleavage. The method has been validated for several reactions and demonstrated in the case of copper triflate catalyzed N2O fragmentation.