Outer electronic shell visualization by NMR chemical shift laplacian of a helium probe

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 3 He NMR chemical shift δ He and its Laplacian ∇ 2 δ He were calculated. The ∇ 2 δ He isosurfaces have symmetrical toroidal shapes along CF axes; the maximum values of ∇ 2 δ 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 ∇ 2 δ 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 3 He NMR spectral characteristics remain sensitive at relatively large distances. © 2018 Wiley Periodicals, Inc.