Theoretical Chemistry Accounts最新文献

Electronic structure methods based on quantum mechanics were employed to characterize elementary steps for the gas-phase thermal decomposition of triazene-bridged nitro-1,2,4-triazole (TBBT). Homolytic C–NO₂ bond scission and ·NO₂ elimination were the most energetically favorable unimolecular paths for the initial decomposition. From there, sequences of unimolecular reactions for daughters of the initiation steps through low-energy β-scission reactions and ring-opening reaction were postulated and characterized. Hydron shift, C–N bond breakage, nitrogen and NO₂ elimination, and small molecules like CN–N=NH obtained were all characterized. Creating a comprehensive network that can be used to develop a detailed limited rate chemical dynamic mechanism for simulating decomposition of TBBT, the results provide the foundation for TBBT’s combustion modeling, and response to its aging, and storage.

In this study, we conducted a theoretical investigation to elucidate the chiral recognition mechanisms of polysaccharide-derived stationary phase for the bunolol β-blocker. DFT calculations provided structural and energetic insights, successfully explaining chiral discrimination and enantiomeric elution order obtained in previous HPLC experiments. Our analysis highlighted the crucial role of hydrogen bonding and π–π stacking interactions in determining the relative stability of the diastereomeric complexes formed between the bunolol and chiral selector.

We employ the four-component relativistic extended–coupled–cluster (ECC) method, a variational coupled–cluster (CC) approach, to compute the permanent electric dipole moment (PDM) of open-shell diatomic molecules (CaH, CaF, SrH and SrF) in their ground electronic state. The ECC results are compared with the PDM values estimated by the experiments as well as other single-reference CC-based approaches (the Z-vector technique, the expectation value method and the finite field approach) within the four-component relativistic framework to test the efficacy of the employed method. Our study reveals that the relativistic ECC method can yield reliable results for the PDMs of the considered molecular systems. We also observe that the computed results of the dipole moment improve upon the augmentation of diffused functions to the basis set.

Structures of pyridinium-based ionic liquids containing 1-methylpyridinium [MP]⁺, 1-ethylpyridinium [EP]⁺ and 1-propylpyridinium [PP]⁺ with halide anions (X) where X = Cl⁻, Br⁻ and I⁻ were studied using density functional theory and the most stable structures of these ionic liquids were compared. Then electronic and structural properties were extracted for the desired liquids. The results show that in the most stable conformers, in these ILs, Cl⁻ and Br⁻ anions prefer to be placed almost in the plane of the pyridinium ring, while I⁻ prefers the position almost vertical to the plane of the pyridinium ring. In order to investigate the hydrogen bonds between molecules by atoms in molecules (AIMs) and natural bonding orbital (NBO) were studied. The calculated thermodynamic functions show that the interaction of the cation–anion pair in ionic liquids containing Cl⁻ and Br⁻ anions is greater than I⁻, and these interactions decrease with the increase in the atomic weight of the halide. Molecular orbital theory has also been used to calculate quantities related to their stability and activity. Also, ionic liquids containing iodine anion have a high dipole moment compared to ionic liquids containing chloride and bromide. The results of this study show that the properties of Any ILs can be controlled by choosing the appropriate anions.

Evaluating the effects of a solvent on the properties of a solute molecule is important to understand its behavior in a solution of that solvent; this, in turn, is important because most reactions—including all the reactions in biological systems—occur in solution. In its most common definition, aromaticity is a property of molecules with delocalized electrons in a ring. It significantly influences their behavior and, therefore, it is important to evaluate the effects of a solvent on it. The most powerful magnetic criterion to estimate aromaticity considers magnetically induced current densities in the ring. The present work applies this approach to adducts of hydroxybenzenes with explicit water molecules. Hydroxybenzenes are selected as the simplest aromatic systems capable of forming solute–solvent hydrogen bonds with water molecules. Hydroxybenzenes without consecutive OH groups are selected to avoid the influence of intramolecular hydrogen bonds between OHs. Current densities are calculated focusing on the aromatic rings, and the effect of the solvent is highlighted by the density changes caused by the presence of the water molecules attached to the hydroxybenzene molecule. The results show that the strength of the ring current decreases as the number of OH groups in the molecule increases. The strength does not change greatly in the adducts with respect to the isolated molecules: the change extent and direction depend mostly on the arrangement of water molecules around the central molecule. The current density maps show that the water molecules may also be involved in the current flow.

We studied intramolecular noncovalent bonds in organogermanium or organosilicon cyclic esters of tris(2-hydroxyalkyl)amines called silatranes and germatranes. We have shown that the N…Si and N…Ge interactions, well known as hypervalent or transannular bonds, can be rightfully categorized as the strong tetrel bonds (TtB). In the wide set of silatranes and germatranes, the TtB strength is under the influence of the Y substituent at Tt atom in the N…Tt–Y fragment and the features of crystalline environment. We have disclosed the quantitative trends in electronic features of N…Tt tetrel bonds and demonstrated the applicability of criteria based on the positions of extremes in electron density and electrostatic potential along the line between N and Tt atoms to compare the strength of the N…Si and N…Ge tetrel bonds. An important observation is that the dependence of gap width on bond lengths is not linear for silatranes. In order to solve this problem we have analyzed the features of total static potential. The gap between positions of extremes in electrostatic and total static potentials is wide for the weak tetrel bonds and narrow for the strong ones.