Tracing the Fingerprint of Chemical Bonds within the Electron Densities of Hydrocarbons: A Comparative Analysis of the Optimized and the Promolecule Densities

Abstract

The equivalence of the molecular graphs emerging from the comparative analysis of the optimized and the promolecule electron densities in two hundred and twenty five unsubstituted hydrocarbons was recently demonstrated [Keyvani et al. Chem. Eur. J. 2016, 22, 5003]. Thus, the molecular graph of an optimized molecular electron density is not shaped by the formation of the C-H and C-C bonds. In the present study, to trace the fingerprint of the C-H and C-C bonds in the electron densities of the same set of hydrocarbons, the amount of electron density and its Laplacian at the (3, -1) critical points associated with these bonds are derived from both optimized and promolecule densities, and compared in a newly proposed comparative analysis. The analysis not only conforms to the qualitative picture of the electron density build up between two atoms upon formation of a bond in between, but also quantifies the resulting accumulation of the electron density at the (3, -1) critical points. The comparative analysis also reveals a unified mode of density accumulation in the case of 2318 studied C-H bonds, but various modes of density accumulation are observed in the case of 1509 studied C-C bonds and they are classified into four groups. The four emerging groups do not always conform to the traditional classification based on the bond orders. Furthermore, four C-C bonds described as exotic bonds in previous studies, for example the inverted C-C bond in 1,1,1-propellane, are naturally distinguished from the analysis.

Absent Diamond-to-β-SnPhase Transition for Carbon: Quantum Chemical Topology Approach

“…To investigate the influence of the atomic rearrangement on the change of during the transition, values for the procrystal densities were calculated (Figure c). In contrast to the related electron density topology, the change of for procrystals along the transition pathway differs from that for the optimized densities, in analogy to the results of other authors . The enhancement of the maximum due to atomic interactions is for the cd ‐type structures significantly stronger than for the β ‐ Sn ‐type structures.…”

“…In contrast to the related electron density topology, the change of P 1 b for procrystals along the transition pathway differs from that for the optimized densities, in analogy to the results of other authors. [65] The enhancement of the P 1 b maximum due to atomic interactions is for the cd-type structures significantly stronger than for the b-Sn-type structures. This can be seen as 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 the evidence of a more covalent bond character in the cd-type structures compared to the b-Sn-type ones.…”

On the Nature of the Positronic Bond

“…Thus, the positron is not capable of forming its own atomic basin in this molecule (even adding a number of extra basis functions to the positronic basis set at the midpoint between the nuclei did not alter this pattern). As discussed recently in details, not the analysis of the topological structure nor the amounts of various property densities at (3, −1) CPs are safe grounds to decipher the nature of AIM interactions. Instead, the atomic properties must be used to dig into the nature of the interactions .…”

On the Uselessness of Bond Paths Linking Distant Atoms and on the Violation of the Concept of Privileged Exchange Channels

“…As no one expects sudden formations or breakings of bonds during molecular vibrations or, what is more, changes in the theoretical method only, bond path cannot mean chemical bond ,,. Moreover, topology of the electron density distribution is mainly governed by atomic densities, whereas the electron density build‐up, which is characteristic for covalent bonds, is rather modest ,. Wick and Clark have also shown that the presence of BPs and BCPs results simply from the Poincaré‐Hopf relationship and the symmetry of the system and does not necessarily mean binding effect …”