Search results for "DFT CALCULATION"
showing 10 items of 81 documents
Effect of electron-withdrawing substituents on the electrophilicity of carbonyl carbons
2005
Indexación: Scopus The substituent effects on the carbonyl carbon atom for a series of twelve substituted phenyl acetates have been rationalized using a global electrophilicity index. This index is linearly correlated with the experimental reaction rate coefficients. We found that, in contrast to the proposed interpretation based on experimental 13C NMR chemical shifts and ground state destabilization calculations, the electrophilicity of carbonyl compounds increases due to the effect promoted by electron-withdrawing groups in these systems. https://www.sciencedirect.com/science/article/pii/S0040402004018046?via%3Dihub
Anion-driven encapsulation of cationic guests inside pyridine[4]arene dimers
2019
Pyridine[4]arenes have previously been considered as anion binding hosts due to the electron-poor nature of the pyridine ring. Herein, we demonstrate the encapsulation of Me4N+ cations inside a dimeric hydrogen-bonded pyridine[4]arene capsule, which contradicts with earlier assumptions. The complexation of a cationic guest inside the pyridine[4]arene dimer has been detected and studied by multiple gas-phase techniques, ESI-QTOF-MS, IRMPD, and DT-IMMS experiments, as well as DFT calculations. The comparison of classical resorcinarenes with pyridinearenes by MS and NMR experiments reveals clear differences in their host–guest chemistry and implies that cation encapsulation in pyridine[4]arene…
Molecular Features Behind Formation of α or β Co-Crystalline and Nanoporous-Crystalline Phases of PPO
2022
Guest molecular features determining the formation of α and β phases of poly(2-6-dimethyl-1,4-phenylene) oxide (PPO) are explored by collecting literature data and adding many new film preparations, both by solution casting and by guest sorption in amorphous films. Independently of the considered preparation method, the α-form is favored by the hydrophobic and bulky guest molecules, while the hydrophilic and small guest molecules favor the β-form. Furthermore, molecular modeling studies indicate that the β-form inducer guests establish stronger dispersive interactions with the PPO units than the α-form inducer guests. Thus, the achievement of co-crystalline (and derived nanoporous crystalli…
One-bond 1 J (15 N,H) coupling constants at sp2 -hybridized nitrogen of Schiff bases, enaminones and similar compounds: A theoretical study
2020
1 J(15 N,H) coupling constants for enaminones and NH-forms of intramolecularly hydrogen-bonded Schiff bases as model compounds for sp2 -hybridized nitrogen atoms are evaluated using density functional theory (DFT) to find the optimal functionals and basis sets. Ammonia is used as a test molecule and its one-bond coupling constant is compared with experiment. A methylamine Schiff base of a truncated molecule of gossypol is used for checking the performance of selected B3LYP, O3LYP, PBE, BHandH, and APFD density functionals and standard, modified, and dedicated basis sets for coupling constants. Both in vacuum and in chloroform, modeled by the simple continuum model of solvent, the modified b…
A DFT study of the vicinal 3J(119Sn,13C) and 3J(119Sn,1H) coupling constants in trimethyl- and chlorodimethyl-stannyl propanoates.
2013
Abstract We have tested the performance of DFT protocols, both at the Scalar relativistic ZORA and non-relativistic level of theory, for the calculation of the 3 J( 119 Sn, 13 C) and 3 J( 119 Sn, 1 H) vicinal couplings for a series of flexible organotin(IV) derivatives with formula XMe2SnCHRCHR′COOMe (X = Me, Cl; R, R′ = Me, Ph). A satisfactory agreement between experimental and calculated vicinal couplings has been obtained by taking into account the conformational behaviour of the compounds investigated. The protocols used, mainly the relativistic one, were found to give a correct picture of the populations and a sufficiently high overall performance in calculating the vicinal couplings, …
Controlling the Formation of Sodium/Black Phosphorus IntercalationCompounds Towards High Sodium Content
2021
The solid-state synthesis of pure sodium-black phosphorus intercalation compounds (Na-BPICs) has been optimized in bulk for two stoichiometric ratios. Specifically, in-situ X-Ray diffraction (XRD) allowed the precise identification of the optimal temperature range for the formation of Na-BPICs: 94°C–96°C. Moreover, as the undesired formation of Na3P takes place at this very same range, we succeeded in introducing a new synthetic route based on a fast-thermal ball milling implementation that results in the bulk production of BPIC without Na3P in 9 out of 10 cases. Finally, by combining XRD, Raman spectroscopy, and DFT calculations we developed a new structural model for Na-based BPICs showin…
Mechanism of photoluminescence in intrinsically disordered CaZrO3 crystals: First principles modeling of the excited electronic states
2017
Abstract CaZrO3 (CZO) powders obtained by the polymeric precursor method at 400 °C, and then, the samples were annealed at different temperatures (400, 600, 800, and 1000 °C) and characterized by X-ray diffraction, Raman and ultraviolet–visible spectroscopic methods, along with photoluminescence (PL) emissions. First principle calculations based on the density functional theory (DFT), using a periodic cell models, provide a theoretical framework for understanding the PL spectra based on the localization and characterization of the ground and electronic excited states. Fundamental (singlet, s ) and excited (singlet, s* , and triplet, t* ) electronic states were localized and characterized us…
Oxidation of diclofenac in the presence of iron(II) octacarboxyphthalocyanine
2021
Abstract This paper presents the results of the research on the influence of catalytic activity of iron(II) octacarboxyphthalocyanines (FePcOC) on the transformation of diclofenac (DCF) which is the most popular anti-inflammatory analgesic. Diclofenac poses a serious threat to the natural environment. The paper demonstrates that diclofenac, in the presence a monomeric form of iron octacarboxyphthalocyanine and hydroxyl radicals (HO•) (from H2O2), undergoes a transformation into diclofenac-2,5-iminoquinone (DCF-2,5-IQ), causing distinct changes in the UV–Vis absorption spectrum. In the presence of iron octacarboxyphthalocyanine and H2O2, the previously colourless diclofenac solution becomes …
Structural and spectroscopic characterisation of 2-(2'-hydroxybenzoyl)pyrrole and its O-methyl derivative
2004
Abstract Density functional theory calculations on the tautomeric and conformational equilibria of 2-(2′-hydroxybenzoyl)pyrrole (HBP) and 2-(2′-methoxybenzoyl)pyrrole (MBP) were performed. Moreover, the experimental IR and UV spectra of the same compounds were recorded and compared with the theoretical data. The presence of an intramolecular hydrogen bond in HBP can be related to the biological activities of some of its derivatives.
Molecular and crystal structure of Ac-(Z)-ΔAbu-NMe2 and Ac-DL-Abu-NMe2 as compared to those of related molecules
2004
Abstract The molecular and crystal structures of two homologous amino acid derivatives: N-acetyl-α,β-dehydro-butyrine N´,N´-dimethylamide (1) and N-acetyl-DL-butyrine N´,N´-dimethylamide (2), have been determined by X-ray crystallography. Similar solid-state association of both compounds is observed; despite different molecular conformation, they form centrosymmetric dimers linked by the intermolecular N–H…O hydrogen bonds. The conformation of two crystallographically independent molecules of 1 [with torsion angles ϕ, ψ, χ 1 ≈ (–47°, 130°, 3°), respectively] is also characteristic of other related diamides – ΔAla, ΔPhe and ΔLeu – previously studied in the solid state. To analyse whether thi…