Comparison of DFT Methods for the Investigation of the Reduction Mechanisms of Aromatic Nitro- and Nitroso Compounds

The main goal of this paper is to find an adequate level of theory for the computational investigation of the reduction mechanisms of aromatic nitro- and nitroso compounds. To this end, five standard reduction potentials of nitro- and nitrosobenzene in three different solvents and four pKa values of species involved in the mechanism were compared with the values calculated at different DFT and CBS-X levels of theory. Out of fourteen tested functionals, five showed good linear correlation between calculated and experimental ΔrG° values. However, at all explored levels of theory, the calculated ΔrG° values systematically deviate from the experimental ones, indicating the necessity of better description of solvation effects for charged species, possibly via a cluster-continuum approach. This work is licensed under a Creative Commons Attribution 4.0 International License

Experimental and Theoretical IR Spectra of 2-Nitrosopyridines

Previously unknown IR spectra of 2-nitrosopyridines 1−3 were recorded in the solid phase after cryogenic photolysis of their dimers, and identified by the comparison with the corresponding theoretical spectra. Optimal results were obtained with double-hybrid (DH) density functionals and def2-TZVP basis set, the best being DSD-PBEP86-D3(BJ), B2GP-PLYP-D3(BJ) and mPW2-PLYP-D2. Experimental frequencies were obtained by scaling harmonic frequencies with appropriate scaling factors, either taken from the literature or calculated using modified HFREQ2014 dataset. In the case of DH functionals, anharmonic frequencies do not offer any advantage in comparison with the scaled harmonic ones. Unexpectedly, all non-DH density functionals, including highly praised ωB97X-V and ωB97M-V, have serious problems with normal modes containing N=O bond stretching vibration. It was concluded that the origin of the problem is in the nitroso group itself, most likely caused by its multireference character. The best results among non-DH functionals were achieved at TPSSh-D3(BJ)/def2-TZVP level of theory. This work is licensed under a Creative Commons Attribution 4.0 International License

Structure, Dynamics and Vibrational Spectra of α-Chloroallyl Cations in Solid SbF5-Matrices

Cis- and frans-α-chloroallyl cations were prepared by matrix isolation method in solid SbF5 matrix, and obtained FT-IR spectra compared with the results of high-level ab-initio calculations. Ionization of either cis- or trans-1,3-dichloropropenes lead to the mixture of cis- and trans-cations, whose interconversion barrier is smaller than for parent allyl cation. The extent of a-chlorine carbocation stabilization was shown to be comparable to that obtained by methyl group. Additionally, the ionization constant of chloro- propenes in the solid SbF5 matrix was measured for the first time

About the Nature of Carbon-Nitrogen Triple Bond in Complexes of Nitriles with Strong Lewis Acids

Complexes of nitriles 1-7 with antimony(V) fluoride in cryogenic matrices were studied by FT-IR spectroscopy. A large increase in C=N stretching frequency induced by complexing with SbF5 is observed in all investigated nitriles. From the vibrational changes of the nitrile molecule skeleton, it was found that the polarity of the nitrile group is increased in the complex. The inductive effect caused by complexing with SbFs was studied by observing the changes of C-CN stretching and CH3 or CH2 deformation vibrations. The qualitative similarity between vibrational changes induced either by complexing or by ionization of nitriles is discussed. Current interpretations of the nitrile effect by rehybridization of nitrogen or by partially antibonding character of the a orbital of CN bond are discussed on the basis of both the IR spectra and high level ab initio calculations

Spectrophotometric Studies of Some Novel Deri vati ves of Pyridinium Chloride

The UV-Vis and IR characteristics of five novel aralkyl derivatives of pyridinium chloride, found to be reversible inhibitors of acetyl-cholinesterase, are reported. The dissociation constants of the individual keto and oxime functional groups were determined spectrophotometrically and discussed in terms of the known pK values of compounds with similar structures. The three examined derivatives of the phenacylpyridinium type contain in solution a considerable proportion of the enol form while their next higher homologues are present predominately in their keto forms. AM1 molecular-orbital calculations show that the much higher acidity of α-CH2 group of benzoylethylpyridinium type compounds is a consequence of an anomeric effect

Complexity of Some Interesting (Chemical) Graphs

Complexity of some interesting polycyclic graphs is expressed in terms of the corresponding spanning trees. Graphs considered were a selection of all connected graphs with four and five vertices, graphs composed of two parts, or more parts, connected by a single edge, the Petersen graph, the Blanuša graph, the Desargues-Levy graph and the Schlegel graph of buckminsterfullerene

On Mathematical Properties of Buckminsterfullerenef

Some of the mathematical properties of buckminsterfullerene are considered, that is, geometrical, topological, group-theoretical and graph-theoretical properties. These mathematical properties are used to predict several structural and chemical properties of buckminsterfullerene

The Detour Matrix and the Detour Index of Weighted Graphs

The detour matrix of a weighted graph and its invariants (the detour polynomial, the detour spectrum, the detour index) are discussed. A novel method for computing the detour matrix of (weighted) graphs is proposed

Graph-Theoretical Correlations - Artifacts or Facts?

»...the Fact is the basis, the foundation; Imagination the building material; the Hypothesis the ground plan to be tested; the Truth or Reality is the building...« J. H. van’t Hof