4.2. The stress tensor trajectories for the isotopomers of formally achiral molecules
The analysis for the dominant, i.e. the strongest torsional bond the C1-N7 BCP used to construct the chirality Cσ, bond-twist Tσ, bond-flexing Fσ and bond-axiality Aσ is presented in Figures 2-3and Table 2(a-b) and Table 3(a-b) . The geometries of the torsional scans are provided in the Supplementary Materials S2 .
For the torsional C1-C2 BCP the presence of non-overlapping Tσ(s) for the CCW and CW torsions demonstrates the uniqueness of the Tσ(s) given the highly symmetrical positioning of the C1-C2 BCP along the containing bond-path, seeScheme 1 and Figures S3 of the Supplementary Materials S3 . The stress tensor trajectories Tσ(s) of the torsional C1-C2 BCP for glycine without isotopic substitution (HH) displays a much smaller extent than occurs with the substitution of the deuterium (HD) or tritium (HT) isotopes. In all three cases HH, HD and HT we can distinguish the presence of the CCW and CW directions of torsions by examination of the C1-C2 BCP Tσ(s). The Sa and Ra stress tensor trajectories Tσ(s) of the torsional C1-C2 BCP , appear to be indistinguishable for the HD glycine, but not for the HT glycine. The Tσ(s) of the non-torsional C-H3/10/D3/T3 BCPsoccur in response to the torsional C1-C2 BCP , see Figure S4 of the Supplementary Materials S4 . The Tσ(s) of the C-D3/T3 BCP corresponding to the DH and DT are larger in extent for the HH glycine. The chirality Cσ determined by the torsional C1-C2 BCP for the formally achiral HH glycine (0.057) in Table S3 of theSupplementary Materials S3 is comparable to the torsional C1-C2BCP in lactic acid that can be seen from inspection ofTable 1 in some of the current authors previous work46 to be 0.078 and -0.077 for the S and R stereoisomers respectively.