σ‐holes and π‐holes: Similarities and differences

σ‐Holes and π‐holes are regions of molecules with electronic densities lower than their surroundings. There are often positive electrostatic potentials associated with them. Through these potentials, the molecule can interact attractively with negative sites, such as lone pairs, π electrons, and anions. Such noncovalent interactions, “σ‐hole bonding” and “π‐hole bonding,” are increasingly recognized as being important in a number of different areas. In this article, we discuss and compare the natures and characteristics of σ‐holes and π‐holes, and factors that influence the strengths and locations of the resulting electrostatic potentials. © 2017 Wiley Periodicals, Inc. Computed electrostatic potentials on 0.001 au surfaces of FSBr (upper left) and SO2 (lower right) showing examples of σ‐holes and π‐holes, respectively. Color ranges, in kcal/mole: red, more positive than 20; yellow, between 20 and 10; green, between 10 and zero; blue, negative. Black hemispheres indicate locations of most positive potentials, the VS,max.