Weak σ-Hole Triel Bond between C H Tr (Tr=B, Al, Ga) and Haloethyne: Substituent and Cooperativity Effects.

The replacement of a CH group of benzene by a triel (Tr) atom places a positive region of electrostatic potential near the Tr atom in the plane of the aromatic ring. This σ-hole can interact with an X lone pair of XCCH (X=F, Cl, Br, and I) to form a triel bond (TrB). The interaction energy between C H Tr and FCCH lies in the range between 2.2 and 4.4 kcal/mol, in the order Tr=B