sigma-holes and -holes: Similarities and differences

sigma-Holes and -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, electrons, and anions. Such noncovalent interactions, sigma-hole bonding and -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 sigma-holes and -holes, and factors that influence the strengths and locations of the resulting electrostatic potentials. (c) 2017 Wiley Periodicals, Inc.