A new method of visualization of lone pairs is proposed using fluorine atoms in fluoroacetylene, trifluoroethylene, and fluoroform (sp, sp 2, and sp 3 hybridized carbons) as an example. The space around fluorines was probed by a helium atom and at each point 3He NMR chemical shift δ He and its Laplacian ∇ 2δ He were calculated. The ∇ 2δ He isosurfaces have symmetrical toroidal shapes along CF axes; the maximum values of ∇ 2δ He are reached at about 1.5 Å from fluorine atom center in the direction roughly coinciding with the lone pair localization. The absolute values of the ∇ 2δ He could be used to quantify the electron-rich regions of lone pairs. The results are compared with more common visualization methods—3D maps of the molecular electrostatic potential and the electron localization function. We show that a helium atom could be used for evaluation of fine features of molecular electronic shell, since 3He NMR spectral characteristics remain sensitive at relatively large distances.
Scopus subject areas
- Computational Mathematics