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Abstract 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 C5H5Tr and FCCH lies in the range between 2.2 and 4.4 kcal/mol, in the order Tr=B+cation above the ring pulls density toward itself and thus magnifies the Tr σ‐hole. The TrB to the XCCH nucleophile is thereby magnified as is the strength of the TrB. This positive cooperativity is particularly large for Tr=B.
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This content will become publicly available on January 27, 2026
Competition Between Halogen Atom and Ring of Halobenzenes as Hydrogen Bond Electron Donor Sites
Abstract A halobenzene molecule contains several sites that are capable of acting in an electron‐donating capacity within a H−bond. One set of such sites comprise the lone electron pairs of the halogen (X) atoms on the periphery of the ring. The π‐electron system above the ring plane can also fulfill this function in many cases. DFT calculations are applied to compare and contrast the propensity of these two site types to engage in such a H−bond within the context of mono, di, tri, tetra, and hexasubstituted halobenzenes. The X atoms chosen for study comprise the full set: F, Cl, Br, and I. It is found that even when the electrostatic potential of the X lone pair is more negative than that above the ring, it is the latter position which is the preferred binding site of HCl in most cases. This preference switches over to the X lone pair only for higher order of substitution, with n=4 or 6. This pattern is explained in large measure by the higher contribution of dispersion when the proton donor is located above the ring.
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- Award ID(s):
- 1954310
- PAR ID:
- 10570385
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPhysChem
- Volume:
- 26
- Issue:
- 7
- ISSN:
- 1439-4235
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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