Rotational barrier and electron-withdrawing substituent effects: Theoretical study of -conjugation in para-substituted anilines

The rotational barrier RB around C–NH2 bond between the minimum and maximum states of 84 electron-withdrawing groups at para-position in aniline were studied at the density functional wB97X-D/6-31G** level. The rotational barrier was found to correlate strongly with shortening of the C–NH2 bond, increase of flattening of NH2 group, decrease in negative natural charge on amino nitrogen, increase in minimum ionization potential around lone pair of amino nitrogen, increase in maximum (positive) electrostatic potential on amino hydrogens, increase in NH2 stretching frequencies, and increase in stabilization energy. The rotational barrier was also found to correlate well with empirical pKa and Hammett σp constants. The rotational barrier is shown to be a reliable quantum mechanical approach to measure p-conjugation in para-substituted anilines. Based on RB a quantitative scale is constructed for the ability of electron-withdrawing substituents to resonate with aniline. A quinone-like structure has been proposed for stronger electron-withdrawing substituents where an extension of resonance stabilization requires the simultaneous presence of electron donor (NH2) and electron-withdrawing groups.

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Computational Studies of Magnesium and Strontium Substitution in Hydroxyapatite

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.529-530.123 ◽

2012 ◽

Vol 529-530 ◽

pp. 123-128 ◽

Cited By ~ 1

Author(s):

Flora E. Imrie ◽

Marta Corno ◽

Piero Ugliengo ◽

Iain R. Gibson

Keyword(s):

Density Functional ◽

Structural Changes ◽

Harmonic Approximation ◽

Site Preference ◽

Ionic Radii ◽

Biologically Relevant ◽

Site Preferences ◽

Mechanical Approach ◽

Quantum Mechanical Approach ◽

Mg Substitution

The properties of hydroxyapatite can be improved by substitution of biologically relevant ions, such as magnesium (Mg) and strontium (Sr), into its structure. Previous work in the literature has not reached agreement as to site preferences in these substitutions, and there are suggestions that these may change with differing levels of substitution. The current work adopted a quantum mechanical approach based on density functional theory using the CRYSTAL09 code to investigate the structural changes relating to, and site preferences of, magnesium and strontium substitution (to 10 mol%) in hydroxyapatites and also to predict the corresponding vibrational spectra in the harmonic approximation. The structures underwent full geometrical optimisation within the P63 space group, indicating an energetic site preference for the Ca (2) site in the case of Mg substitution, and the Ca (1) site in the case of Sr. Shrinkage of the unit cell was observed in the case of Mg substitution, and expansion in the case of Sr substitution, in agreement with the corresponding ionic radii. Thermodynamic properties of the structures obtained from the harmonic vibrational frequency calculations confirmed that the structures were minima on the potential energy surface. Isotopic substitutions indicated that the main contribution of Sr and Mg to vibrational modes is at frequencies < 400 cm-1.

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Integrating Density Functional Theory Modeling with Experimental Data to Understand and Predict Sorption Reactions: Exchange of Salicylate for Phosphate on Goethite

Soil Systems ◽

10.3390/soilsystems4020027 ◽

2020 ◽

Vol 4 (2) ◽

pp. 27 ◽

Cited By ~ 1

Author(s):

James D. Kubicki ◽

Tsutomu Ohno

Keyword(s):

Density Functional Theory ◽

Density Functional ◽

Mineral Water ◽

Surface Complexes ◽

Functional Theory ◽

Complex Models ◽

Mechanical Approach ◽

Plant Exudates ◽

Quantum Mechanical Approach

Density functional theory (DFT) calculations are a quantum mechanical approach that can be used to model chemical reactions on an atomistic scale. DFT provides predictions on structures, thermodynamics, spectroscopic parameters and kinetics that can be compared against experimentally determined data. This paper is a primer on the basics of utilizing DFT for applications in mineral-water interfaces. In our case-study, we use DFT to model the surface complexes of phosphate and salicylate adsorbed onto the (101) and (210) surfaces of α-FeOOH (goethite), as an example of combining DFT and experiment. These three components are important in the phosphorus-organic matter interactions in soils, and by comparing the energies of the two surface complexes, the exchange energy of salicylate for phosphate onto goethite can be estimated. The structures of the surface complexes are predicted and the resulting vibrational frequencies calculated based on these structures are compared to previous observations. Upon verification of reasonable surface complex models, the potential energy of exchanging salicylate for phosphate is calculated and shown to be significantly exothermic. This model result is consistent with observations of plant exudates, such as salicylate freeing adsorbed phosphate in soils under P-limited conditions.

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Study on the CO Formation Mechanism during Coal Ambient Temperature Oxidation

Energies ◽

10.3390/en13102587 ◽

2020 ◽

Vol 13 (10) ◽

pp. 2587

Author(s):

Shuo Liu ◽

Yuguo Wu ◽

Chunshan Zhou ◽

Jianming Wu ◽

Yulong Zhang

Keyword(s):

Density Functional Theory ◽

Ambient Temperature ◽

Density Functional ◽

Basis Set ◽

Functional Theory ◽

Temperature Oxidation ◽

Ambient Temperatures ◽

Mechanical Approach ◽

Aldehyde Groups ◽

Quantum Mechanical Approach

The CO formation rules of coal were analyzed by a self-developed testing device under ambient temperature. The changes of functional groups caused by oxidation were obtained using Fourier-transform infrared spectroscopy (FTIR). The experimental results showed that CO was generated during the ambient temperature oxidation. The highest concentration level of CO could be 389 ppm. The methylene and aldehyde groups on the side chains were involved in the reaction. For the quantum mechanical approach, we employed the density functional theory with the 6–31 G (d, p) basis set. Density functional theory–based computations interpreted the possible reaction sites on a coal molecule by electronic static potential analysis. The rationality of the predicted reactions was also evaluated by transition state analysis and energy analysis. This research theoretically proved that coal could be oxidized to carbon monoxide under ambient temperatures and gave the possible reaction paths.

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Effect of π-conjugated molecules on electronics properties of benzene-diamine derivatives

Iraqi Journal of Physics (IJP) ◽

10.30723/ijp.v19i50.658 ◽

2021 ◽

Vol 19 (50) ◽

pp. 70-76

Author(s):

Mohsin Al-Khaykanee ◽

Ali Al-Jawdahb

Keyword(s):

Band Gap ◽

Density Functional ◽

Conjugated Molecules ◽

Functional Theory ◽

Pi Conjugated ◽

Phenyl Rings ◽

Mechanical Approach ◽

Quantum Mechanical Approach ◽

Chemical Groups ◽

Theoretical Results

The present work shows a theoretical results that have been used the functional Hybrid of three parameters Lee-Yang-Parr (B3LYP) of the quantum mechanical approach for density functional theory with (Spanish Initiative for Electronic Simulations with Thousands of Atoms) SIESTA code. All calculations were carried out employing the used method at the Gaussian 09 package of programs. It was reported the main point for research on dominance of the bandgap of elongated pi-conjugated molecules by using different chemical groups replacing hydrogen atom in the most molecules that used in this work. The side groups creates another factor that controls the value of the band gap. The dihedral angle between the two phenyl rings plays more important role in controlling the band gap in these molecules.

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Rotational Barrier and Conjugation: Theoretical Study of Resonance Stabilization of Various Substituents for the Donors NH2 and OCH3 in Substituted 1,3-Butadienes

Indonesian Journal of Chemistry ◽

10.22146/ijc.42850 ◽

2019 ◽

Vol 19 (4) ◽

pp. 1055

Author(s):

Ali Hussain Yateem

Keyword(s):

Density Functional ◽

Theoretical Study ◽

Amino Nitrogen ◽

Conjugated Systems ◽

Rotational Barriers ◽

Out Of Plane ◽

Resonance Stabilization ◽

The Difference ◽

Internal Rotational Barriers ◽

Single Bonds

The barrier to internal rotation around the central C2–C3 single bond of a series of (1E)-monosubstituted 1,3-butadienes and (1E,3E)-1-Y-4-X-disubstituted butadienes, with Y=NH2 or OCH3 and X=NO2, CHO, COOH, CN, CF3, Cl or F, were studied at the density functional w B97X-D/6-31G∗∗ level. The effect of substituents on π-conjugation in disubstituted 1,3-butadienes was studied by correlating the calculated internal rotational barriers with the difference in structural, atomic and molecular properties between the transition state TS and the s-trans conformers. The calculated differences in lengths of C–C, C–NH2 and C–OCH3 single bonds, N-H-N, and C-O-CH3 angles, NH2 out-of-plane angle, natural charges on amino nitrogen and methoxy oxygen, and the maximum electrostatic potential on amino hydrogens, were found to correlate strongly with the rotational barriers. The conjugative interaction was strongly stabilized in the case of strong π-electron acceptors such as NO2 or CHO and is slightly or negligibly affected with Cl and F groups. The resonance stabilization with the remaining acceptors decreases in the order COOH > CN > CF3. Acceptors X maintain their relative order of stabilization for the two donors, and NH2 is more stabilizing. Dominant resonance structures are suggested for highly and negligibly conjugated systems.

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Extremely large third-order nonlinear optical effects caused by electron transport in quantum plasmonic metasurfaces with subnanometer gaps

Scientific Reports ◽

10.1038/s41598-020-77909-y ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Takashi Takeuchi ◽

Kazuhiro Yabana

Keyword(s):

Electron Transport ◽

Plasmon Resonance ◽

Density Functional ◽

Nonlinear Optical ◽

Third Order ◽

The Third ◽

Optical Responses ◽

Mechanical Approach ◽

Third Order Nonlinearity ◽

Quantum Mechanical Approach

AbstractIn this study, a third-order nonlinear optical responses in quantum plasmonic metasurfaces composed of metallic nano-objects with subnanometer gaps were investigated using time-dependent density functional theory, a fully quantum mechanical approach. At gap distances of ≥ 0.6 nm, the third-order nonlinearities monotonically increased as the gap distance decreased, owing to enhancement of the induced charge densities at the gaps between nano-objects. Particularly, when the third harmonic generation overlapped with the plasmon resonance, a large third-order nonlinearity was achieved. At smaller gap distances down to 0.1 nm, we observed the appearance of extremely large third-order nonlinearity without the assistance of the plasmon resonance. At a gap distance of 0.1 nm, the observed third-order nonlinearity was approximately three orders of magnitude larger than that seen at longer gap distances. The extremely large third-order nonlinearities were found to originate from electron transport by quantum tunneling and/or overbarrier currents through the subnanometer gaps.

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Substituent effects in the reaction of aromatic amines and peroxydisulfate

Canadian Journal of Chemistry ◽

10.1139/v69-618 ◽

1969 ◽

Vol 47 (19) ◽

pp. 3710-3713 ◽

Cited By ~ 10

Author(s):

N. Venkatasubramanian ◽

A. Sabesan

Keyword(s):

Nitrogen Atom ◽

Carbon Atom ◽

Aromatic Amines ◽

Substituent Effects ◽

Substituted Anilines ◽

Electrophilic Attack ◽

Effect Of Substituents ◽

Hammett Constants ◽

Kinetics Of ◽

Electron Withdrawing Substituents

The kinetics of the reaction between aromatic amines and the peroxydisulfate ion in aqueous basic conditions have been investigated. The effect of substituents has been studied by employing about 25 ortho-, meta-, and para-substituted anilines. The reaction is accelerated by electron-releasing substituents and is retarded by electron-withdrawing substituents, pointing to an electrophilic attack by the S2O82− ion. A better correlation between rate and the Hammett constants is obtained for an electrophilic attack at the nitrogen atom of the amine rather than at the carbon atom of the amine. A good correlation also exists between the log k2 values and the pKb of the corresponding amines.

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DFT Modelling of Molecular Structure, Vibrational and UV-Vis Absorption Spectra of T-2 Toxin and 3-Deacetylcalonectrin

Materials ◽

10.3390/ma15020649 ◽

2022 ◽

Vol 15 (2) ◽

pp. 649

Author(s):

Dmitrii Pankin ◽

Mikhail Smirnov ◽

Anastasia Povolotckaia ◽

Alexey Povolotskiy ◽

Evgenii Borisov ◽

...

Keyword(s):

Density Functional ◽

Quantum Mechanical ◽

Theoretical Studies ◽

Vibrational States ◽

Mechanical Approach ◽

Vibrational Spectroscopies ◽

Quantum Mechanical Approach ◽

Dft Modelling ◽

Identification And Characterization

This paper discusses the applicability of optical and vibrational spectroscopies for the identification and characterization of the T-2 mycotoxin. Vibrational states and electronic structure of the T-2 toxin molecules are simulated using a density-functional quantum-mechanical approach. A numerical experiment aimed at comparing the predicted structural, vibrational and electronic properties of the T-2 toxin with analogous characteristics of the structurally similar 3-deacetylcalonectrin is performed, and the characteristic spectral features that can be used as fingerprints of the T-2 toxin are determined. It is shown that theoretical studies of the structure and spectroscopic features of trichothecene molecules facilitate the development of methods for the detection and characterization of the metabolites.

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