Contour line diagram

Distributions Ap(r) have been determined for various derivatives of 1 by both ab initio and X-ray diffraction studies66. In Figure 10, a contour line diagram of Ap(r) in the ring plane of cis, cw-1,2,3-tricyanocyclopropane is shown66a. Positive difference densities are found between the three C atoms, but the Ap(r) maxima are displayed up to 0.3 A from the intemuclear axis66. The displacement of the maxima is considered to indicate the bent bond character of the CC bonds of 1. 

Figure 16 Contour line diagrams of the Laplacian distribution V p(r) of (a) ArF (b) ArH (c) HArF. Solid lines give areas of charge concentration (V p(r) < 0), while dashed lines give areas of charge depletion (V p(r) > 0). The solid line connecting the atomic nuclei is the bond path. The solid lines that cross the bond path at the bond critical point show the zero-flux surface crossing the shown plane. (Ref 37. Reproduced by permission of Springer Verlag)...

Figure 3.1 Schematic representations of a) a water molecule orientation near a nonpolar CHs-group, which is optimal if none of the hydrogen atoms or electron pairs is directed toward the nonpolar group ( = 0) b) contour line diagrams of three polar molecules with the first inner line of a solvation energy o/O kcal/mol, the second line of 1 kcal, the third line of 2 kcal/mol e/c and c) of the hydrophobic effect. Upon association of hydrophobic particles water or other solvent molecules are released. Entropy grows.

Figure 6 shows a contour line diagram of the electron density distribution of the van der Waals complex Hcj (He,He distance 2.74 A). The electron density at the midpoint between the two He atoms is just 0.008 e/A, quite different from the values found for a typical covalent bond between first-row elements (1-5 e/A ). Despite the smallness of p(r) in the internuclear region, the He nuclei are linked by a MED path and the midpoint is the position of a (3, — 1) critical point (Fig. 6). As pointed out above this does not imply the existence of a chemical bond. The energy density H(r) is positive at the (3, — 1) critical point, which means that the kinetic energy rather than the potential energy dominates in the internuclear region. There is no chemical bond between the He atoms.

Fig. 6a and b.. Perspective drawing (a) and contour line diagram (b) of the electron density distribution p(r) of He2 at its van dcr Waals distance (2.74 A) shown with regard to a plane that rantains the nuclei. MED path and (3, — 1) critical point are indicated in the contour line diagram. (HF/6-31G(p) calculations)... 

Investigation of the Laplace concentration — V p(r) of Hex " provides additional information. In Fig. 8, perspective drawings and contour line diagrams of — V p(r) are given for both the X E ground state and the excited state of HeN" ". The valence shell concentration of N ( P) is highly anisotropic. There are concentration lumps in the direction of the singly occupied 2p(7t) orbitals and deep concentration holes in the direction of the unoccupied 2p(a)... 

The contour line diagram in Fig. 8b reveals that the electronic structure of both He and N ( P) are hardly distorted in the X Z ground state of HeN". The pa-hole slightly widens on the side of the He atom (the elliptic concentration areas are shifted slightly to the back) such as to increase stabilizing electrostatic interactions. This is in line with the description given above. 

It is interesting to note that the pn electrons of Ne and Ar may lead to some destabilization of NgX . In Fig. 10, contour line diagrams and perspective drawings of -V p(r) are shown for the ground state and the excited state of ArC " " [5]. The ground state corresponds to C ( S) which does not possess any p electrons the excited state corresponds to C ( P), which possesses a a-hole but also a 2p electron (compare with Fig. 9). In the ArC " " states, the valence shell concentration of the Ar atom is distorted in a characteristic way. There are holes in the direction of the bond while there are concentration lumps in the nonbonding region of Ar. Distortions in the valence shell concentration of the C atom are complementary to those at the Ar atom, i.e. the... 

Fig. lOa-f. Contour line diagrams and perspective drawings of the Laplace concentration, — V p(r), of ArC (a, b) state, (c, d) state, direction of filled a-orbital and (e, f) 11 state, direction of unfilled Jt-orbital. In the contour line diagrams inner shell concentrations are no longer shown. Ref. [13]... 

Fig. 11. Profile plot along the internuclear axis (above) and contour line diagram (below) of the difference electron density Ap(r) = —...

Fig. 22. Contour line diagram of the Laplace concentrations, — V p(r), of HeCCH. The inner shell concentrations are no longer shown. (HF/...

Contrary to He and Ne, Ar forms a covalently bound ArCN ( i ) ion with CN ( S ) (see Ar, C in Table 15). This is in line with the enhanced donor ability of Ar and the distinct acceptor ability of CN f S" ) at its carbon end. Figure 24, which contains contour line diagrams and perspective drawings of calculated Laplace-concentration of ArCN and ArNC", reveals pronounced ipa-dona-tion of the Ar atom and concentration of negative charge in the ArC bonding... 

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