Quantification of Intramolecular (-) and (+) Charge-Assisted Hydrogen Bond Energy via Molecular Tailoring Approach:...

The energies of O-H···O^- and N⁺-H···O charge-assisted hydrogen bonds quantified via the method based on molecular tailoring approach for a series of anionic and cationic compounds. The energies of O-H···O^- and N⁺-H···O charge-assisted hydrogen bonds vary from 15 to 43 and from 5 to 29 kcal/mol, being five and seven times stronger, on average, respectively, than conventional intramolecular hydrogen bonds in neutral prototypes. The strengthening of (-) and (+) charge-assisted hydrogen bonds in anions and cations relative to conventional hydrogen bonds in neutral compounds is accompanied by significant changes in the structural, spectral and theoretical hydrogen bond descriptors. The hydrogen bond geometry changes, the spectral manifestations of (-) and (+) charge-assisted hydrogen bonds and process of electron transfer through hydrogen bond become more pronounced compared to conventional hydrogen bonds. The energies of (-) and (+) charge-assisted hydrogen bonds and conventional hydrogen bonds are functionally related to the values of hydrogen bond descriptors, allowing the former to be evaluated using the latter. It has been shown that the energies of (-) and (+) charge-assisted hydrogen bonds are the strongest of the known types of hydrogen bonds and belong in most cases to the category of strong hydrogen bonds.