Effects of Halogen Bond, Hydrogen Bond, and π‐Tetrel Bond on the Internal CC Bond of Halogenated Ethylene

Depending upon the level of halogenation, the electrostatic potential of the π region above the molecular plane of an alkene can vary over a wide range and can be either positive or negative. The ability of H 2 CCHX, H 2 CCFX, and F 2 CCFX, where X=F, Cl, Br, I, to interact with either a nucleophile or electrophile, is studied by DFT calculations. This binding is compared with the σ‐hole CX···N halogen bonding with NH 3 . The negative potential above H 2 CCHX facilitates ClH···π H‐bonding with HCl, while NH 3 can bind to the positive π‐hole above F 2 CCFX; the partially halogenated H 2 CCFX is able to act as both nucleophile and electrophile. The introduction of a σ‐hole XB acts to generally weaken the CC bond of H 2 CCHX, but the effect is less unambiguous for the more highly halogenated alkenes. These effects are reversed upon the formation of a π‐tetrel bond with NH 3 . The largest perturbations are associated with the π‐HB, which causes a sizable CC bond weakening. Combination of two sorts of intermolecular bonds is cooperative when the central alkene acts as both electron donor and acceptor and anticooperative when it acts as double acceptor.