Transfer of electron density as a result of hydrogen bond formation

Abstract

It has been found that the amount of charge transfer between donor and acceptor molecules in four sets of hydrogen-bonded complexes may be adequately described as an exponential function of the equilibrium distance between the hydrogen atom and the nearest atom of the acceptor molecule. The exponential factors of the transfer are of the same order but somewhat larger than the factors found otherwise in the investigations of dynamic electron transfer.

Towards physical interpretation of Hammett constants: charge transferred between active regions of substituents and a functional group

“…It was previously shown that charges of the substituent active region, qSAR(X), correlated fairly well with the Hammett constants in monosubstituted benzenes [62], carboxylic acids [58,63], and substituted tetrazoles [64]. On the other hand, the constants correlated well with the properties of reaction sites, e.g., with the charges and potentials at H atoms of COOH group [58].…”

“…On the other hand, the constants correlated well with the properties of reaction sites, e.g., with the charges and potentials at H atoms of COOH group [58].…”

“…Namely, it was found that the replacement of the substituent charges by charges of the so-called substituent active regions SARs (where SAR is a unit composed of a substituent and the carbon atom, C ipso , to which the substituent is attached) allowed to correlate a property related to substituents with Hammett constants. For example, good correlations of the SAR charges with the Hammett constants and with charges of acidic H in COOH functional group were obtained, for five classes of substituted aromatic carboxylic acids [58].…”

“…The substituent constants were frequently correlated with the properties of atoms and bonds in the nearest vicinity of the reaction center [34-39, 41, 42, 47, 53-60], e.g., the hydrogen atom when dissociation of the COOH group was considered [37, 58,63]. The Hammett constants were also correlated with properties characterizing whole molecules [16,43,[46][47][48][49][50][51][52].…”

“…-electron densities at p-and m-positions in monosubstituted benzenes [34] -electrostatic potential values at the ring carbon atoms [28,35,36] -electrostatic potential values at atoms of a reaction center [28,37] -topography of electrostatic potential near the molecular surface [38][39][40][41][42] -hyperpolarizability [43] -a complexed metal chemical shift [44,45] -energy of the highest occupied orbital (E HOMO ) [46,47] -energy of the lowest unoccupied orbital (E LUMO ) [16] -ionization potential [48] -electrophilicity, being a measure of stabilization in energy when the system acquires an additional electronic charge DN from the environment [28,49,50] -core electron binding energy shifts [51,52] -intramolecular charge transfer between oxygen or sulfur lone pair and an adjacent orbital, both within the reaction active center [53,54] -the so-called quantum chemical topology descriptors constructed using properties of the bond critical points, BCP, where BCP is the saddle points in the electron density [55][56][57][58] -charge of the reaction active site [42,47,59,60] -energy of p-conjugation [61] -charge of the substituent active space [58,[62][63][64].…”