title: 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.
authors.affiliation: Faculty of Chemistry, Department of Pure Chemistry, Shahid Beheshti University, G. C., Tehran, 19839, Evin, P.O. Box 19395-4716, Iran), Tel/Fax: (98) 2122-431-661.
authors.forename: Zahra Alimohammadi
authors.initials: ZA
authors.lastname: Keyvani
authors.affiliation: Faculty of Chemistry, Department of Pure Chemistry, Shahid Beheshti University, G. C., Tehran, 19839, Evin, P.O. Box 19395-4716, Iran), Tel/Fax: (98) 2122-431-661. chemist_shant@yahoo.com.
authors.forename: Shant
authors.initials: S
authors.lastname: Shahbazian
authors.affiliation: Faculty of Chemistry, Department of Pure Chemistry, Shahid Beheshti University, G. C., Tehran, 19839, Evin, P.O. Box 19395-4716, Iran), Tel/Fax: (98) 2122-431-661.
authors.forename: Mansour
authors.initials: M
authors.lastname: Zahedi
keywords: bond theory; electron density; hydrocarbons; molecular modeling; topological analysis