Enhancement of Halogen Bond Strength by Intramolecular H-Bonds

Abstract

Quantum calculations study the potential of an intramolecular H-bond between the halogen atom (X) of a halobenzene and a substituent placed ortho to it, to amplify the ability of X to engage in a halogen bond (XB) with a Lewis base. H-bonding substituents NH2, CH2CH2OH, CH2OH, OH, and COOH were added to halobenzenes (X = Cl, Br, I). The amino group had little effect, but those containing OH increased the CX···N XB energy to a NH3 nucleophile by about 0.5 kcal/mol; the increment associated with COOH is larger, nearly 2 kcal/mol. These energy increments were approximately doubled if two such H-bonding substituents are present. Combining a pair of ortho COOH groups with an electron-withdrawing NO2 group in the para position has a particularly large effect, raising the XB energy by about 4 kcal/mol, which can amount to as much as a 4-fold magnification.

Elucidating the Role of Electron-Donating Groups in Halogen Bonding

“…These interactions promote further polarization of the halogen atom, generating a more positive V S,max and larger E bind compared to EDGs in the meta or para positions. The side interactions, known as hydrogen bond-enhanced halogen bonds (HBeXB), have been reported to improve the interaction strength and stability of XB complexes in the literature. − ,,, The BH 2 substituent is the exception to this trend. When at the ortho position, it yields the smallest V S,max and weakest E bind compared to meta or para positions that are comparable.…”

“…This electronegative region can behave as a Lewis base forming hydrogen bond (HB) or XB interactions. These additional interactions with the electronegative belt have been shown recently to enhance the strength of the XBs in complexes. − …”

Computational Risk Assessment of Persistence, Bioaccumulation, and Toxicity of Novel Flame-Retardant Chemicals

“…Different degrees of halogenation patterns with an aromatic ring structure are responsible for the electron-withdrawing effect of the halogenated chemicals . This is because the presence of halogen atoms enhances the ability of molecules to form a halogen bond with electron-accepting groups . Furthermore, the global reactivity properties such as chemical potential, chemical hardness, and electrophilicity index were computed to examine the persistent nature of NBFRs in the environment (Table and Supporting Information Table S4).…”

A Model Halogen-Bonded Network as a Potential Tube-like Host for Li+: A DFT Study

“…Because of its highly directional and tunable character [26][27][28][29][30][31][32], the halogen bond has found applications in a wide variety of fields including organic synthesis [33,34], catalysis [35][36][37][38], medicinal chemistry [39][40][41][42][43], and supramolecular chemistry [44][45][46][47][48][49][50][51][52][53][54][55]. The sigma hole of the halogen atom in D-X has also found applications in the recognition, binding, and even transport of electron-rich species such as anions and certain metals that effectively act as halogen-bond acceptors [56][57][58][59][60][61][62][63][64][65][66][67][68][69].…”