Search results for "Calculation"
showing 10 items of 594 documents
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…
Structure and vibrational features of the protic ionic liquid 1,8-diazabicyclo[5.4.0]-undec-7-ene-8-ium bis(trifluoromethanesulfonyl)amide, [DBUH][TF…
2022
Abstract The Protic Ionic Liquid (PIL) formed by neutralization of the super-strong base 1,7-diazabicyclo[5.4.0]undec-7-ene (DBU) with the super-strong acid bis(trifluoromethanesulfonyl)-imide (TFSI), indicated as [DBUH][TFSI], has been investigated. Its chemical physical properties and structural features have been explored using a synergy of experimental and computational tools. Molecular Dynamics-rationalised X-ray diffraction patterns highlight the major role played by hydrogen bonding (HB) in affecting morphology in this PIL. A comparison between HB features in this and in related PILs has been presented, on the base of far-IR experiments and DFT analysis. Indications of a weaker HB in…
Molecular dynamics simulations of elementary chemical processes in liquid water using combined density functional and molecular mechanics potentials.…
1997
The first molecular dynamics (MD) simulation of a chemical process in solution with an ab initio description of the reactant species and a classical representation of the solvent is presented. We study the dynamics of proton (deuterium) transfer in strongly hydrogen-bonded systems characterized by an energy surface presenting a double well separated by a low activation barrier. We have chosen the hydroxyl-water complex in liquid water to analyze the coupling between the reactive system and the environment. The proton is transferred from one well to the other with a frequency close to 1 ps−1 which is comparable to the low-frequency band associated to hindered translations, diffusional transl…
Deuterium hyperfine splittings in the rotational spectrum of NH2D as revealed by Lamb-dip spectroscopy
2020
Abstract In the context of radio-astronomical observations, laboratory experiments constitute a cornerstone in the interpretation of rich line surveys due to the concomitant presence of numerous emitting molecules. Here, we report the investigation of three different rotational transitions of mono-deuterated ammonia (NH2D), a species of astrophysical interest, for which the contribution of the deuterium nuclear spin to the rotational spectrum has been resolved for the first time in the millimeter- and submillimeter-wave domain. The effect of hyperfine interactions on the rotational spectrum has been unveiled by a combined theoretical and experimental approach. Quantum-chemical calculations …
Understanding C C bond formation in polar reactions. An ELF analysis of the Friedel Crafts reaction between indoles and nitroolefins
2013
[EN] The Friedel-Crafts (FC) reaction of N-methyl indole 1 with nitroethylene 2 has been studied using DFT methods at the B3LYP/6-31+G** level in order to characterize the bonding changes along the C-C bond-formation process in polar reactions. For this FC reaction a two-step mechanism has been found. The first step is associated with the C-C bond formation between the most electrophilic centre of nitroethylene and the most nucleophilic centre of N-methyl indole, to yield a zwitterionic intermediate IN. The second step corresponds to an intramolecular proton transfer process at IN, regenerating the aromatic system present at the indole. Despite the high electrophilic character shown by nitr…
Theoretical study of spiropyran-merocyanine thermal isomerization.
2004
Abstract Quantum mechanical computations at DFT level were carried out on the processes involved in the thermal reaction SP ⇆ ME, where SP is the nitro-substituted spirobenzopyran (1 ′ ,3 ′ -dihydro-1 ′ ,3 ′ ,3 ′ -trimethyl-6-nitro-spiro[2H-1-benzopyran-2,2 ′ - [2H]indole]) in the closed form and ME is the corresponding open form. A detailed theoretical description of the overall reaction is reported along with the thermodynamic parameters for all intermediates and transition states. The obtained activation energy value is in agreement with the available experimental data in solution.
Microwave, High-Resolution Infrared, and Quantum Chemical Investigations of CHBrF2: Ground and v4 = 1 States
2011
A combined microwave, infrared, and computational investigation of CHBrF(2) is reported. For the vibrational ground state, measurements in the millimeter- and sub-millimeter-wave regions for CH(79)BrF(2) and CH(81)BrF(2) provided rotational and centrifugal-distortion constants up to the sextic terms as well as the hyperfine parameters (quadrupole-coupling and spin-rotation interaction constants) of the bromine nucleus. The determination of the latter was made possible by recording of spectra at sub-Doppler resolution, achieved by means of the Lamb-dip technique, and supporting the spectra analysis by high-level quantum chemical calculations at the coupled-cluster level. In this context, the…
CO2 and CH2 Adsorption on Copper-Decorated Graphene: Predictions from First Principle Calculations
2022
Calculations were performed using Latvian Super Cluster (LASC), located in Center of Excellence at Institute of Solid State Physics, the University of Latvia, which is supported by European Union Horizon2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under Grant Agreement No. 739508, project CAMART2. The authors would like to express their gratitude for funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 768789 (CO2EXIDE project). In the last stage of investigation and during the preparation of the publication, the authors were assisted by the postdoc D.B. with his own funding from project No. 1.1.1.2/VIAA/l/16/147 (…
Ion-Track Template Synthesis and Characterization of ZnSeO3 Nanocrystals
2022
A.I.P. thanks the Institute of Solid-State Physics, University of Latvia. ISSP UL as the Center of Excellence is supported through the Framework Program for European universities. The work was carried out within the framework of the grant AP05134367 of the Ministry Funding: The work was carried out within the framework of the grant AP05134367 of the Ministry of education and Science Science of of the Republic Republic of Kazakhstan.