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We present a computational analysis of hexaphenylethane derivatives with heavier tetrels comprising the central bond. In stark contrast to parent hexaphenylethane, the heavier tetrel derivatives can readily be prepared. In order to determine the origin of their apparent thermodynamic stability against dissociation as compared to the carbon case, we employed local energy decomposition analysis (LED) and symmetry‐adapted perturbation theory (SAPT) at the DLPNO‐CCSD(T)/def2‐TZVP and sSAPT0/def2‐TZVP levels of theory. We identified London dispersion (LD) interactions as the decisive factor for the molecular stability of heavier tetrel derivatives. This stability is made possible owing to the longer (than C−C) central bonds that move the phenyl groups out of the heavily repulsive regime so they can optimally benefit from LD interactions., Carbon‐Carbon bonds are exceptional as demonstrated for the hexaphenylditetrels where attractive London dispersion interactions are the decisive factor for the thermodynamic stabilities of tetrels other than carbon. Structural and energetic comparisons show that even though hexaphenylethane displays the largest dispersion energy between the two molecular halves, it has remained elusive because of even larger Pauli repulsion of the phenyl moieties that are forced in close contact due to the C−C bond that is the shortest in this series.

Chemistry - A European Journal, 27 (25), ISSN:0947-6539, ISSN:1521-3765

The mechanism of the adsorption and grafting of diazonium cations onto the surface of graphyne and graphdiyne was investigated using Density Functional Theory (DFT). The adsorption energy (both in vacuum and water as solvent) of the phenyl diazonium cation was evaluated at three different positions of the graphyne and graphdiyne surface. Moreover, the lowest energy adsorption sites were used to calculate and plot Non-covalent Interactions (NCI). The Bond Dissociation Energy (BDE) results (up to 66 kcal/mol) for the scission of the phenyl group support the remarkable stability of the grafted layer. As both of these materials are non-dispersible in aqueous solution, in this work through the use of Molecular Mechanics (MM) and Molecular Dynamics (MD) we explored also the effect of the grafted substituted aryl groups derived from aryldiazonium salts onto the solvation properties of these materials.

Understanding the hydrogen atom abstraction (HAA) reactions of N-heterocyclic carbene (NHC)-boranes is essential for extending the practical applications of boron chemistry. In this study, density functional theory (DFT) computations were performed for the HAA reactions of a series of NHC-boranes attacked by &bull, CH2CN, Me&bull, and Et&bull, radicals. Using the computed data, we investigated the correlations of the activation and free energy barriers with their components, including the intrinsic barrier, the thermal contribution of the thermodynamic reaction energy to the kinetic barriers, the activation Gibbs free energy correction and the activation zero-point vibrational energy correction. Furthermore, to describe the dependence of the activation and free energy barriers on the thermodynamic reaction energy or reaction Gibbs free energy, we used a three-variable linear model, which was demonstrated to be more precise than the two-variable Evans&ndash, Polanyi linear free energy model and more succinct than the three-variable Marcus-theory-based nonlinear HAA model. The present work provides not only a more thorough understanding of the compositions of the barriers to the HAA reactions of NHC-boranes and the HAA reactivities of the substrates but also fresh insights into the suitability of various models for describing the relationships between the kinetic and thermodynamic physical quantities.

The noble gas (Ng) binding ability of a monocationic [(FLP)Au]+ species has been investigated by a computational study. Here, the monocationic [(FLP)Au]+ species is formed by coordination of Au(I) cation with the phosphorous (Lewis base) and the boron (Lewis acid) centers of a frustrated Lewis pair (FLP). The bonds involving Au and P, and Au and B atoms in [(FLP)Au]+ are partially covalent in nature as revealed by Wiberg bond index (WBI) values, electron density analysis and energy decomposition analysis (EDA). The zero point energy corrected bond dissociation energy (D0), enthalpy and free energy changes are computed for the dissociation of Au-Ng bonds to assess the Ng binding ability of [(FLP)Au]+ species. The D0 ranges from 6.0 to 13.3 kcal/mol, which increases from Ar to Rn. Moreover, the dissociation of Au-Ng bonds is endothermic as well as endergonic for Ng = Kr-Rn, whereas the same for Ng = Ar is endothermic but exergonic at room temperature. The partial covalent character of the bonds between Au and Ng atoms is demonstrated by their WBI values and electron density analysis. The Ng atoms get slight positive charges of 0.11–0.23 |e|, which indicates some amount of charge transfer takes place from it. EDA demonstrates that electrostatic and orbital interactions have equal contributions to stabilize the Ng-Au bonds in the [(FLP)AuNg]+ complex.

In order to predict the impact sensitivity of high explosives, we designed and evaluated several models based on the trigger linkage hypothesis and the Arrhenius equation. To this effect, we calculated the heat of detonation, temperature of detonation, and bond dissociation energy for 70 energetic molecules. The bond dissociation energy divided by the temperature of detonation proved to be a good predictor of the impact sensitivity of nitroaromatics, with a coefficient of determination (R2) of 0.81. A separate Bayesian analysis gave similar results, taking model complexity into account. For nitramines, there was no relationship between the impact sensitivity and the bond dissociation energy. None of the models studied gave good predictions for the impact sensitivity of liquid nitrate esters. For solid nitrate esters, the bond dissociation energy divided by the temperature of detonation showed promising results (R2 = 0.85), but since this regression was based on only a few data points, it was discredited when model complexity was accounted for by our Bayesian analysis. Since the temperature of detonation correlated with the impact sensitivity for nitroaromatics, nitramines, and nitrate esters, we consider it to be one of the leading predictive factors of impact sensitivity for energetic materials. Electronic supplementary material The online version of this article (10.1007/s00894-019-4269-z) contains supplementary material, which is available to authorized users.

International audience; Nitrene transfer reactions to various hydrocarbon molecules can be efficiently catalyzed by Fe complexes through a mechanism reminiscent of the oxygen transfer function of oxygenase enzymes. Such enzymes exhibit a high-valent iron oxo Fe(IV) = O as the active species, and it has also been proposed that an analogous species, i.e., Fe(IV) = NR (NR being the nitrene group) is responsible for the nitrene transfer activity. We describe here the influence of the Fe(IV) coordination sphere on some key parameters for nitrene transfer efficacy, such as the spin state of the Fe(IV) cation, the electronic affinity, and the bond dissociation energy of the NHR moiety. We explore here the electronic properties of Fe(IV) = NTs (NTs = tolylsulfonylimido group) mononuclear complexes with ligands involving phenolate and nitrogen donor groups, as catalytic properties with such ligands have been found to be quite promising. Six tetradentate ligands were studied, which derive from three different scaffolds: 2-methylenepyridine-N,N-bis(2-methylene-4,6-dichlorophenol) and 2-methylenepyridine-N,N-bis(2-methylene-4,6-dimethylphenol), N,N-dimethyl-N’,N’-bis(2-methylene-4,6-dichlorophenol) ethylenediamine, and N,N-dimethyl-N’,N’- bis(2-methylene-4,6-dimethylphenol) ethylenediamine, N,N’-bis(2-methylene-4,6-dichlorophenol)-N,N’-dimethyl-1,2-diaminoethane and N,N’-bis(2-methylene-4,6-dimethylphenol)-N,N’-dimethyl-1,2-diaminoethane. Thanks to thorough DFT computations, we present some rationalization of the electronic properties of the resulting Fe(IV) = NTs complexes in relation to their coordination sphere and compare them to other Fe(IV) nitrene active species. We show in particular the important role of the anionic character and strong π-donation of the phenolate groups.

In this work, we computationally investigated from quantum chemical calculations (DFT) at the BP86 level with the various basis sets def2-SVP, def2-TZVPP, and TZ2P+, chemical bonding issues of the recently described carbene-analogues gold(I) complexes AuCl-NHEMe (Au1-NHE) with E = C – Pb. The optimized structures and the metal-ligand bond dissociation energy (BDE) were calculated, and the nature of the E→Au bond was studied with charge and energy decomposition methods. The equilibrium structures of the system showed that there were major differences in the bonded orientation from the ligands NHC-NHPb to gold(I) complex between the lighter and the heavier homologues. The BDEs results showed that the metal-carbene analogues bonds were very strong bonds and the strongest bond was calculated for Au1-NHC which had the bond strength De = 79.2 kcal/mol. Bonding analysis of Au1-NHE showed that NHE ligands exhibited donor-acceptor bonds with the σ lone pair electrons of NHE donated into the vacant orbital of the acceptor fragment (AuCl). The EDA-NOCV results indicated that the ligand NHE in Au1-NHE complexes were strong σ-donors and very weak π donor and the bond order in complexes was Au1-NHC > Au1-NHSi > Au1-NHGe > Au1-NHSn > Au1-NHPb. We also realised that the gold-ligand bond was characterized by a π back-donation component from the Au to the ligand. All investigated complexes in this study were suitable targets for synthesis and gave a challenge in designing Au nano-crystals of narrow size distribution from gold(I) complexes that carried versatile N-heterocyclic carbene-analogues NHE.

Background The rapid access to intrinsic physicochemical properties of molecules is highly desired for large scale chemical data mining explorations such as mass spectrum prediction in metabolomics, toxicity risk assessment and drug discovery. Large volumes of data are being produced by quantum chemistry calculations, which provide increasing accurate estimations of several properties, e.g. by Density Functional Theory (DFT), but are still too computationally expensive for those large scale uses. This work explores the possibility of using large amounts of data generated by DFT methods for thousands of molecular structures, extracting relevant molecular properties and applying machine learning (ML) algorithms to learn from the data. Once trained, these ML models can be applied to new structures to produce ultra-fast predictions. An approach is presented for homolytic bond dissociation energy (BDE). Results Machine learning models were trained with a data set of >12,000 BDEs calculated by B3LYP/6-311++G(d,p)//DFTB. Descriptors were designed to encode atom types and connectivity in the 2D topological environment of the bonds. The best model, an Associative Neural Network (ASNN) based on 85 bond descriptors, was able to predict the BDE of 887 bonds in an independent test set (covering a range of 17.67–202.30 kcal/mol) with RMSD of 5.29 kcal/mol, mean absolute deviation of 3.35 kcal/mol, and R 2 = 0.953. The predictions were compared with semi-empirical PM6 calculations, and were found to be superior for all types of bonds in the data set, except for O-H, N-H, and N-N bonds. The B3LYP/6-311++G(d,p)//DFTB calculations can approach the higher-level calculations B3LYP/6-311++G(3df,2p)//B3LYP/6-31G(d,p) with an RMSD of 3.04 kcal/mol, which is less than the RMSD of ASNN (against both DFT methods). An experimental web service for on-line prediction of BDEs is available at http://joao.airesdesousa.com/bde. Conclusion Knowledge could be automatically extracted by machine learning techniques from a data set of calculated BDEs, providing ultra-fast access to accurate estimations of DFT-calculated BDEs. This demonstrates how to extract value from large volumes of data currently being produced by quantum chemistry calculations at an increasing speed mostly without human intervention. In this way, high-level theoretical quantum calculations can be used in large-scale applications that otherwise would not afford the intrinsic computational cost.

The total oxidation of C2H2, C3H6, C3H8, n-C4H8, n-C4H10 and i-C4H10 was studied in a monolithic flow reactor under temperature-programmed mode and highly diluted conditions. The non-catalytic combustion of the investigated hydrocarbons leads to a substantial formation of CO and traces of methane at intermediate temperatures. This drawback was suppressed upon the deposition of a thin layer of Co3O4 on the monolith and all investigated hydrocarbons tend to light off at 250-290 degrees C. The apparent activation energy was found to exhibit a linear correlation with the C-H bond dissociation energy, indicating that the C-H activation is still the rate-limiting step. (C) 2009 Elsevier B.V. All rights reserved.

The radical reduction of B-alkylcatecholboranes into alkanes using alcohols and water as hydrogen atom source is described. This process involves a completely unexpected mechanism: the alcohol (or water) complexed to a borate derivative acts as a reducing agent. The complexation activates the alcohol resulting in a decrease of the O–H bond dissociation energy. This approach offers promising opportunities for the development of tin-free radical reducing agent. Closely related reports from the recent literature involving boron and titanium derivatives are also presented.

Bond dissociation energies (BDEs) of all possible A-X single bonds involving the first- and second-row atoms, from Li to Cl, where the free valences are saturated by hydrogens, have been estimated through the use of the G3-theory and at the B3LYP/6-311+G(3df,2pd)//B3LYP/6-31G(2df,p) DFT level of theory. BDEs exhibit a periodical behavior. The A-X (A = Li, Be, B, Na, Mg, Al, and Si) BDEs show a steady increase along the first and the second row of the periodic table as a function of the atomic number Z(X). For A-X bonds involving electronegative atoms (A = C, N, O, F, P, S, and Cl) the bond energies achieve a maximum around Z(X) = 5. The same behavior is observed when BDEs are plotted against the electronegativity χ(X) of the atom X. Thus, for A-X bonds (A = Li, Be, B, Na, Mg, Al, Si), the BDEs for a fixed A increases, grosso modo, as the electronegativity differences between X and A increase, with some exceptions, which reflect the differences in the relaxation energies of the radicals produced upon the bond cleavage. A similar trend, albeit less pronounced, is found for single A-X bonds, where A = C, N, O, F, P, S, and Cl. However, there is an additional feature embodied in the enhancement of the strength of the A-boron bonds due to the ability of boron to act as a strong electron acceptor. The trends in bond lengths and charge densities at the bond critical points are in line with the aforementioned behavior. © 2005 American Chemical Society.

The accurate O-H bond dissociation enthalpies for a series of meta and para substituted phenols (X-C 6 H 4 -OH, X=H, F, Cl, CH 3 , OCH 3 , OH, NH 2 , CF 3 , CN, and NO 2 ) have been calculated by using the (RO)B3LYP procedure with 6-311G(d,p) and 6-311++G(2df,2p) basis sets. The proton affinities of the corresponding phenoxide ions (X-C 6 H 4 -O - ) have also been computed at the same level of theory. The effect of change of substituent position on the energetics of substituted phenols has been analyzed. The correlations of Hammett’s substituent constants with the bond dissociation enthalpies of the O-H bonds of phenols and proton affinities of phenoxide ions have been explored. Keywords: Substituted Phenol, Bond Dissociation Energy, Acidity, DFT. I. Introduction Phenols are widely used as synthetic organic materials and also as antioxidants in living organisms [1]. Phenoxyl radicals are known as important intermediates in many biological and industrial applications [2]. Phenols are of special interest in organic chemistry, since their acid-base equilibria have often been used as reference values in establishing linear free energy relationships [3]. Consequently, much effort has been put to understand the factors governing the O-H bond dissociation energies, BDE(O-H), and acidities of substituted phenols, both in the solution and gas phase [4-11].

The OH bond dissociation energies (BDEs) of ellipticine-derived hydroxylated compounds have been evaluated by a kinetic method and are shown to correlate with the cytotoxic activity of these derivatives.