The Cis -Effect Explained Using Next-Generation QTAIM.

We used next-generation QTAIM (NG-QTAIM) to explain the cis -effect for two families of molecules: C 2 X 2 (X = H, F, Cl) and N 2 X 2 (X = H, F, Cl). We explained why the cis -effect is the exception rather than the rule. This was undertaken by tracking the motion of the bond critical point ( BCP ) of the stress tensor trajectories T σ ( s ) used to sample the U σ -space cis- and trans-characteristics. The T σ (s) were constructed by subjecting the C1-C2 BCP and N1-N2 BCP to torsions ± θ and summing all possible T σ (s) from the bonding environment. During this process, care was taken to fully account for multi-reference effects. We associated bond-bending and bond-twisting components of the T σ (s) with cis- and trans- characteristics, respectively, based on the relative ease of motion of the electronic charge density ρ ( r b ). Qualitative agreement is found with existing experimental data and predictions are made where experimental data is not available.