Intermolecular bond critical point

Figure 1.2.3 shows similar graphs for the water dimer, where it is clearly seen that only one intermolecular bond critical point exists, corresponding to a H O bond. In this figure one can also see two O-H intramolecular bond critical points, whose features are not fully shown due to the contours selected (those for the water molecule on the right side are not seen due to the out-of plane position of its two O-H bonds). As shown in Table 1.2.1, the intramolecular and intermolecular bond critical points differ in their properties (only one intramolecular bond is shown in Table 1.2.1, as all four bonds of this type have similar features). These data allow a... 

TABLE 2.2. Electronic Density Parameter at Bond Critical Points for Intermolecular Hydrogen Bonding in 2-Acetyl-l,8-dihydroxy-3, 6-dimethylnaphthalene"... 

Figure 3.17 Electron density at the bond critical point (in an) versus intermolecular distance (in A) obtained for hydrogen-bonded (HB) and dihydrogen-bonded (DHB) complexes. Solid circles and triangles correspond to B3LYP calculations. Open circles and triangles represent MP2 calculations. The solid and dashed lines are fittings to the exponential function for B3LYP and MP2, respectively. (Reproduced with permission from ref. 31.)...

Once we have established what a hydrogen bond is and its relative position within the possible intermolecular bonds, we can focus our attention in the forms conventionally used to identify its presence. Besides the direct criteria described before as part of defining its nature (compute the energy of the interaction and search for a H- - -X bond critical point in the A-H- - -X... 

Table 1.2.1 Characteristic parameters of the intermolecular (0--H) and intramolecular (O-H) bond critical points found in the water dimer of Fig. 1.2.3. All values are given in atomic units.

In an electron density (ED) study using multipolar refinement, Bach et al7 have analyzed the intermolecular interactions of the type C-F -O and C-F---F-C associated with pentafluorobenzoic acid at 110 K. These studies highlight the discrepancies in the experimental and theoretical values of the Laplacian at the bond critical points of C-F and examined the energetic disadvantage of the F - F interaction. Bianchi et al have shown that in the ( )-l,2-bis(4-pyridyl)ethylene... 

A set of criteria have been proposed to establish weak intermolecular bonding interactions, such as CH4- -OH2 (hydrogen bond ), F2- -CO (halogen bond ) or Ar- -C02 (van der Waals bond). For example, the criteria necessary to conclude that a hydrogen bond X—H- -B is present are as follows [61] (i) the existence of a bond critical point and a bond path H- -B, (ii) an appropriate value of pb (the typical range is between 0.002 and 0.034 au). 

Another environmentally benign solvent is supercritical water, which has a great potential to replace conventional solvents, although it requires rather harsh experimental conditions tc = 374 °C and Pc = 218 atm see Table 3-4) [224, 225]. At the critical point of SC-H2O, its volume is three times larger than that at ambient temperature, its relative permittivity is only 5.3 (compared to e, = 78.4 at 25 °C), and its intermolecular hydrogen-bond network is partially broken. Under supercritical conditions, water consists of small clusters, oHgomers, and even monomeric gas-like water molecules [226,... 

H-bonds intermolecular H-bonds Tr-electron delocalization topological parameters critical points QTAM (Quantum Theory Atoms in Molecules method) covalent hydrogen bonds interaction energy decomposition scheme. 

---