Where the two carbon atoms touch in the triple bond in disubstituted acetylenes: the AIM analysis

Optimization of 24 disubstituted acetylenes YCCX with Y=Li, H, F and X=H, F, Li, Na, OH, BeH, NH2, BH2, NO2 was carried out at the MP2/6-311++G(d,p) level of theory. The analysis of structural parameters (bond lengths, atomic radii) and atoms in molecules theory (AIM) topological parameters (electron densities and their Laplacians in bond critical points) leads to the conclusion that the AIM parameters are much more sensitive to the action of intramolecular perturbations (like substituents) than traditional structural parameters like bond lengths (or bond angles). In particular, the shape of the atom strongly depends on electronegativity of its neighboring atom in the molecule and the effect is transmitted even over a few bonds.