Topological Properties of the Electron Distribution in Hydrogen‐bonded Systems

Abstract

The hydrogen bond (HB) is the most important weak interaction found in nature. It is responsible for the three dimensional shape of biopolymers (proteins and nucleic acids) and for the structure of water, in both the liquid and solid phases. Life processes extensively use the making and breaking of HBs as part of concatenated reactions involving huge amounts of biomolecules. In addition, it has profound implications in the mode of action of drugs and in molecular packing, recognition, and crystal engineering [1].In the literature, the moieties involved in HB interaction are usually identified as hydrogen donor (or electron acceptor) and hydrogen acceptor (or electron donor). In this chapter the donor (D) and acceptor (A) terms are schematically represented as DaHÁÁÁA.The HÁÁÁA interaction distance d(HÁÁÁA) varies from 1.2 to 2.5 Å (or up to 3.0 Å , depending of the criteria used). This is not true for covalent bonds, for which the range is much smaller. Dependence of hydrogen bond properties on the internuclear distance can, therefore, be clearly observed for hydrogen bonds (HBs), as shown by the DaH bond distance, which seems to depend on d(HÁÁÁA). The mutual dependence of bond distances on both sides of the hydrogen atom can easily be understood in terms of the bond-order model proposed by Pauling, which assumes a total valence equal to 1 for the hydrogen atom involved in the HB interaction [2][3][4][5].Similar dependencies have been found for the electron-density properties from application of QTAIM methodology to the hydrogen bond. Topological analysis of rðrÞ was initially used to identify the presence of HB interactions. Thus, characterization of CaHÁÁÁO hydrogen bonds has been used to generalize a set of criteria to establish the presence of hydrogen-bonding interactions based on the QTAIM theory [6]. These criteria have been applied to the study of other hydrogen bonds apart from CaHÁÁÁO interactions, and a further extension has been 425

Glyoxal oligomers: A computational study

“…However, previous reports have shown that this correlation should be exponential when larger ranges of distances are considered [45,46].…”

Examining a Transition from Supramolecular Halogen Bonding to Covalent Bonds: Topological Analysis of Electron Densities and Energies in the Complexes of Bromosubstituted Electrophiles

“…This behavior differs from the tendencies observed in the studies of HB complexes (which showed negative ∇ 2 ρ values, with the magnitudes increasing exponentially with the decreasing the bond length in the covalent-bond region 18 ) However, similar positive or small negative Laplacian values were found earlier for the other covalent bonds formed by the highly polar atoms, which suggests that the Laplacian values of BCPs are not always a reliable indicator to allow an accurate covalent or noncovalent bond type assignment. 43 Therefore, the local energy density H ( r ) was proposed to complete the identification of the interatomic interactions. 43 Positive and negative values of H ( r ) have been used as an alternative way of defining ionic and covalent bonds because this quantity avoids the problems observed for ∇ 2 ρ( r ) with some covalent bonds.…”

1hJFHcoupling in 2‐fluorophenol revisited: Is intramolecular hydrogen bond responsible for this long‐range coupling?

“…It is also noted that the calculated energies for the LP 2 (F)!s*OH interactions (close to 1 kcal mol -1 ) are too small to characterize it as a hydrogen bond. In the current literature [6,21,22] , it is accepted that the QTAIM method is more reliable than the NBO [17] approach to characterize hydrogen bonds. Ruling out the existence of a hydrogen bond for defining the preferential conformations for compounds 1 and 2, it is interesting to analyze how the 4 J FH SSCC involving the hydroxyl proton is transmitted.…”