![]() ![]() ![]() Note that Bader’s theory Atoms-in-Molecules, whereby the concept of chemical bond is replaced with ‘chemical bonding’, efficiently resolves some structural problems. In contrast, a chemical bond is a vague concept because its strict criteria are absent, and when selecting chemical bonds in the molecule, chemists are guided by intuition (in most cases, such an ‘intuitive approach ’ works well but there are debatable examples, especially related to coordination compounds, endohedral complexes, molecules with multicenter chemical bonds ). Herewith, the application of Equation (8) to the vertices seems stricter as the atoms in the molecules are uniquely identified. However, the use of Equation (8) most understandable by chemists is based on counting inequivalent graph vertices and graph edges corresponding to quintessential chemical concepts, atoms, and chemical bonds. The development of the above approach went through the consideration of only empirical formula, empirical formula and atomic valences, diversity of the edges (chemical bonds) in the graph, its automorphic transformations, and the adjacency matrix (see review ). Įlements X classified with criterion α may be different. We also mention in brief other chemical applications such as signal processing when molecules act as signal carriers (e.g., in the molecular switches based on the transits between the isomeric species). The second group deals with the quantum-chemical analysis of the electron density distribution in the molecules and redistribution upon their chemical transformations (e.g., see ). These applications have been systematically reviewed in previous works. The first group of the applications deals with the information entropy of molecular graphs that is very seminal for introducing various entropy-based topological descriptors for physical organic chemistry, digital chemistry, and QSAR/QSPR studies (quantitative structure–activity and structure–property relationships). As follows from the names of the points, information entropy is mainly applied to the molecular species described with the finite mathematical models. ‘Pure’ chemical applications of information entropy are wide and could be separated over the two major areas: (a) analysis of molecular graphs and (b) analysis of electron density of molecules. ![]()
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