Electron density at the BCP

The strength of a chemical bond, reflected in its bond order (BO), is strongly correlated to the electron density at the BCP (pj) [63] ... 

The major conclusion of their paper is the experimental proof of the presence of a genuine, covalent Co-Co bond. However, their conclusion is not reached in a straightforward manner because based on the Laplacian (Figure 14) one might conclude that the Co-Co interaction is not shared. Also, the electron density at the BCP between the two cobalt atoms is small. Based on the observations made in F2 and invoking the functions ( )159 [ ( ) = F(r) + G(r)] and G(r)/p(r) Macchi et al. conclude that the Co-Co is far from the closed-shell limit and we do not find any reason for not considering it a shared interaction as suggested by common chemical sense. ... 

Four bowl-shaped polyaromatic hydrocarbons (C30H12) were investigated with DFT in the context of carbon nanotubes. Bond orders were determined via the electron density at the BCPs. The authors note a discrepancy between the deduced bond order and the eUipticity. Bonds at the inside of the bowl, where p is highest, show smaller eUipticity values than those at the periphery where p is lower. 

Ijjaali et al explored the singlet and triplet PES involved in the gas-phase reactions between N+ and ammonia with high-level ab initio techniques. The electron density at the BCP for the singlet is slightly higher and the energy density more negative than for the triplet. 

The values of electron density and Laplacian of electron density at the BCP for all of these hydrogen bonds meet Popelier s criteria. The range of variation of the properties of the BCP for well-defined hydrogen bonds (p>0.015a.u., V )>0.044 a.u.) may be used for further classification of other intramolecular interactions in DNTs. An analysis of the elhpticity of these hydrogen bonds ( <0.09) and the distance between BCP and RCP (Lp > 1.5 a.u.) does not indicate arty instability of these interactions, and these values also may be used as a reference for further consideration. 

The second group of hydrogen bonds includes interactions that do not meet BCP criteria. The value of the Laplacian of the electron density at the BCP is smaller than 0.024 a.u. for the C5-H...O-P bond in the north/anti conformer of CMP and the C3-H...N3 bond in the north/syn conformer of GMP (Table 5.5). Therefore these interactions should be considered to be electrostatic interactions rather than real hydrogen bonds. They are characterized by the longest H...O distances (more than 2.7 A), small values of the C-H... O angles (less than 122°), and the electron density at BCP (p< 0.006). In addition, these interactions have relatively high ellipticity at the BCP (e>0.19) and a shorter distance to the RCP (Lj < 1.1 a.u ). 

Table 10.3 Bonding characteristics of some diatomic molecules is the equilibrium distance between the nuclei, bcp(H) the distance of the BCP from the H atom, both in A, pbcp the electron density at the BCP in e q(A) the charge of atom A in e, M(A) and M(H) are the atomic dipole moments of A and H, and Mmoi is the molecular dipole moment (all in a.u.) Adapted from [46],...

Fig. 17.16 Linear relationship between the Be —> F and the Cl N charge transferred (CT(e)) and the electron density at the BCP of the Be - F and the C1--N linkages for ternary complexes BeF2 FCl N-base (N-base = NH3, NHCHj, NCH)...

In a conventional covalent bond like the carbon-carbon bond in ethane (Fig. 1), the electron density at the bcp is greater than the sum of the electron densities of the... 

Fig. 5 The bond critical point little black square) illustrated in HC=N. The electron density (p) is represented by three constant-p contour lines, at p = 0.001, 0.287 and 0.486 a.u., which act as boundary values. The four colours used mark the regions bounded by each of three these boundaries for example, the points in the yellow region have an electron density between 0.001 and 0.287 a.u. The electron density at the bond critical point (BCP) between H and C is 0.287 a.u., and this BCP marks the contact point between H and the C=N fragment. The electron density at the BCP between C and N is 0.486 a.u., and this BCP is the contact point between C and N...

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