Resonance Energy in Benzene Derivatives with a Variable Functional Group

2001 ◽  
Vol 66 (11) ◽  
pp. 1623-1637 ◽  
Author(s):  
Otto Exner ◽  
Stanislav Böhm
Keyword(s):  
Density Functional ◽  
Substituent Effects ◽  
Resonance Energy ◽  
Correlation Coefficients ◽  
Principal Component ◽  
Unsaturated Hydrocarbon ◽  
Enthalpies Of Formation ◽  
Isodesmic Reactions ◽  
The Density Functional Theory ◽  
Reaction Energies

Three isodesmic reactions were investigated in which a variable substituent is transferred from a saturated to an unsaturated hydrocarbon residue: ethane → ethene, methane → benzene, ethane → benzene. Their reaction energies could serve as a measure of substituent resonance ability. They were calculated for 31 substituents by the density functional theory (DFT) at the B3LYP/6-311+G(d,p) level, and served as a model for systematic comparison of the DFT energies and experimental enthalpies of formation ∆fH°(298). It turned out that calculations at this level are more reliable than experiments; they disagree sometimes with ∆fH°(298) measured at different times and in different laboratories but agree better with the values calculated by simple additive scheme. Some particularly suspicious values were pointed out. The DFT reaction energies of the isodesmic reactions, ∆1E-∆3E, were correlated with the standard scales of resonance and with other scales of substituent effects by multiple linear regression and principal component analysis. The three scales are fairly similar to each other (correlation coefficients 0.68-0.83), depend rather strongly on resonance (75% of the variance) but involve still at least one component which could not be explained in terms of common substituent effects. Certainly they do not depend - not even slightly - on the inductive effect, steric effect or polarizability.

Estimation of Resonance Energy from Forced Nonplanar Conformations of Conjugated Molecules

2005 ◽  
Vol 70 (10) ◽  
pp. 1577-1588
Author(s):  
Stanislav Böhm ◽  
Otto Exner
Keyword(s):  
Density Functional ◽  
Classical Model ◽  
Minimum Energy ◽  
Resonance Energy ◽  
Isodesmic Reactions ◽  
Conjugated Molecules ◽  
Functional Theory ◽  
Resonance Effects ◽  
The Density Functional Theory ◽  
Derivatives Of

Energies of 39 derivatives of buta-1,3-diene in the twisted conformation were calculated within the framework of the density functional theory at the B3LYP/6-311+G(d,p) level. By comparing with the same molecules in their natural minimum-energy conformations, a scale of resonance effects of various substituents was obtained and expressed in terms of isodesmic reactions. Comparison with other similar scales revealed that this model is not particularly advantageous, its main shortcoming being the relatively small effect. In any case it confirmed that the scales of resonance effects obtained from different models are only very roughly proportional: the classical model of resonance works well in representative examples but has its clear limitation when unduly extended.

scholarly journals Basis Set Effects in the Description of the Cl-O Bond in ClO and XClO/ClOX Isomers (X = H, O, and Cl) Using DFT and CCSD(T) Methods

2019 ◽  
Vol 2019 ◽  
pp. 1-23 ◽  
Author(s):  
Kenneth Irving ◽  
Martina Kieninger ◽  
Oscar N. Ventura
Keyword(s):  
Density Functional ◽  
Basis Set ◽  
Basis Sets ◽  
Enthalpies Of Formation ◽  
Isodesmic Reactions ◽  
Dft Methods ◽  
Functional Methods ◽  
The One ◽  
Isomeric Structures ◽  
Different Sources

The performance of a group of density functional methods of progressive complexity for the description of the ClO bond in a series of chlorine oxides was investigated. The simplest ClO radical species and the two isomeric structures XClO/ClOX for each X = H, Cl, and O were studied using the PW91, TPSS, B3LYP, PBE0, M06, M06-2X, BMK, and B2PLYP functionals. Geometry optimizations and reaction enthalpies and enthalpies of formation for each species were calculated using Pople basis sets and the (aug)-cc-pVnZ Dunning sets, with n = D, T, Q, 5, and 6. For the calculation of enthalpies of formation, atomization and isodesmic reactions were employed. Both the precision of the methods with respect to the increase of the basis sets, as well as their accuracy, were gauged by comparing the results with the more accurate CCSD(T) calculations, performed using the same basis sets as for the DFT methods. The results obtained employing composite chemical methods (G4, CBS-QB3, and W1BD) were also used for the comparisons, as well as the experimental results when they are available. The results obtained show that error compensation is the key for successful description of molecular properties (geometries and energies) by carefully selecting the method and basis sets. In general, expansion of the one-electron basis set to the limit of completeness does not improve results at the DFT level, but just the opposite. The enthalpies of formation calculated at the CCSD(T)/aug-cc-pV6Z for the species considered are generally in agreement with experimental determinations and the most accurate theoretical values. Different sources of error in the calculations are discussed in detail.

DIRECT DENSITY FUNCTIONAL THEORY DYNAMICS STUDY FOR THE CH3OCF2CF2OCH3 + OH REACTION

2011 ◽  
Vol 10 (02) ◽  
pp. 231-244 ◽  
Author(s):  
HONG-BO YU ◽  
FENG-CHAO CUI ◽  
YONG-XIA WANG ◽  
HONG-XIA LIU ◽  
JING-YAO LIU
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Theoretical Data ◽  
State Theory ◽  
Stationary Points ◽  
Enthalpies Of Formation ◽  
Oh Radicals ◽  
Isodesmic Reactions ◽  
Functional Theory ◽  
Barrier Heights

The mechanism and kinetics of the reaction of CH3OCF2CF2OCH3 with OH radicals have been studied theoretically by a direct density functional theory dynamics method. All possible H -abstraction channels and displacement processes taking place on two different conformers of CH3OCF2CF2OCH3 have been taken into consideration. The potential energy surface information including the optimized geometries and harmonic vibrational frequencies of all the stationary points and barrier heights involved in these channels were obtained at the BB1K/6-31+G(d,p) level of theory. The rate constants were calculated using improved canonical variational transition state theory (ICVT) with the small-curvature tunneling correction (SCT) over the temperature range of 200–2000 K. The overall rate constant for the title reaction, which was obtained by considering the weight factor of each conformer from the Boltzman distribution function, is in reasonable agreement with the available experimental value. Three-term Arrhenius expression is fitted to be k T = 1.56 × 10-20 T 2.47 exp (-124.64/ T ) cm 3 molecule-1 s-1 (200–2000 K). Also, the enthalpies of formation of the reactant CH3OCF2CF2OCH3 and product radicals CH3OCF2CF2OCH2 and CH3OCF2CF2O , which lack experimental or theoretical data, were evaluated via applying isodesmic reactions.

Basis Set Effects in the Description of the Cl-O Bond in ClO and XClO Isomers (X=H,O,Cl) Using DFT and CCSD(T) Methods

2018 ◽  
Author(s):  
Oscar Ventura ◽  
Kenneth Irving ◽  
Martina Kieninger
Keyword(s):  
Density Functional ◽  
Basis Set ◽  
Basis Sets ◽  
Enthalpies Of Formation ◽  
Isodesmic Reactions ◽  
Dft Methods ◽  
Functional Methods ◽  
The One ◽  
Isomeric Structures ◽  
Different Sources

<p>The performance of a group of density functional methods of progressive complexity for the description of the ClO bond in a series of chlorine oxides was investigated. The simplest ClO radical species as well as the two isomeric structures XClO/ClOX for each X=H, Cl and O were studied using the PW91, TPSS, B3LYP, PBE0, M06, M06-2X, BMK and B2PLYP functionals. Geometry optimizations as well as reaction enthalpies and enthalpies of formation for each species were calculated using Pople basis sets and the (aug)-cc-pVnZ Dunning sets, with n=2-6. For the calculation of enthalpies of formation, atomization as well as isodesmic reactions were employed. Both the precision of the methods with respect to the increase of the basis sets, as well as their accuracy, were gauged by comparing the results with the more accurate CCSD(T) calculations, performed using the same basis sets as for the DFT methods. The results obtained employing composite chemical methods (G4, CBS-QB3 and W1BD) were also used for the comparisons, as well as the experimental results when they are available. The results obtained show that error compensation is the key for successful description of molecular properties (geometries and energies) by carefully selecting method and basis sets. In general, expansion of the one-electron basis set to the limit of completeness does not improve results at the DFT level, but just the opposite. The enthalpies of formation calculated at the CCSD(T)/aug-cc-pV6Z for the species considered are generally in agreement with experimental determinations, and the most accurate derived theoretically up to present. Different sources of error in the calculations are discussed in detail.</p>

Mechanism of α-acetyl-γ-butyrolactone synthesis

2013 ◽  
Vol 67 (6) ◽  
Author(s):  
Wei Wang ◽  
Sheng-Wan Zhang ◽  
Mei-Ping Li ◽  
Ying-Yu Ren
Keyword(s):  
Reaction Mechanisms ◽  
Density Functional ◽  
Reaction Rate ◽  
Enthalpies Of Formation ◽  
Direct Reaction ◽  
Salting Out ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Alkaline Conditions ◽  
Ester Condensation

AbstractThe mechanism of α-acetyl-γ-butyrolactone (ABL) synthesis from γ-butyrolactone (GBL) and ethyl acetate (EtOAc) was explored by detecting the material changes involved and the enthalpies of formation of the synthons, products, and possible intermediates were calculated using the density functional theory. GBL forms a carbanion of γ-butyrolactone by losing an α-H under strongly alkaline conditions. ABL is then obtained via two reaction mechanisms. One of the reaction mechanisms involves direct reaction of the carbanion of GBL with EtOAc to produce ABL. The other involves the formation of a carbanion of α-(2-hydroxy-tetrahydrofuran-2-yl)-γ-butyrolactone through the reaction of two molecules of GBL, and the subsequent combination of this anion with EtOAc to produce ABL. ABL is thus formed through the above two kinds of competitive ester condensation reactions. It is unnecessary to take into account synthons’ local thickness, and their self-condensation under these conditions. Both reactions of the carbanion of GBL with EtOAc and GBL are exothermic, so the control of their reaction rate is the key to their security. Considering the reasons above, this work applied synthon as the solvent, and avoided environmental pollution by alkylbenzene; also, accidents such as red material and fire were avoided by specific surface area of sodium metal control. Effective isolation of the organic and aqueous phases was performed using the salting out method. Thus, an environmentally friendly, safe, simple, and efficient new method for the synthesis of ABL with the yield higher than 90 % has been established.

scholarly journals Pereskia aculeata vibrational model by Raman characterization and DFT method

2021 ◽  
Vol 9 (1) ◽  
pp. 485-505
Author(s):  
Quesle Martins ◽  
Natali Felix Arinos ◽  
Cristian Aguirre ◽  
Jorge Brito de Faria
Keyword(s):  
Density Functional ◽  
Principal Component ◽  
Dft Method ◽  
Vibrational Modes ◽  
Good Correspondence ◽  
Functional Theory ◽  
Single Scale ◽  
The Density Functional Theory ◽  
Molecular Group ◽  
Raman Characterization

Raman scattering was used to obtain vibrational modes in a Pereskia aculeata sample. The obtained spectrum was compared with quercetin's theoretical spectra, kaempferol, isorhamnetin, rutinose, caffeic, and tartaric acid, generated from the density functional theory (DFT) method, which used structures of the known composition present in the sample. Among the main compounds, phenolic acids and flavonoids are mentioned. Vibrational signatures, designated as CO and CH group modes, are abundant and bands in the region between 800 and 1800 cm-1. This showed that the theoretical and experimental results had good correspondence between the flavonoids. Statistical observations of correlation and principal component analysis (PCA) were used, which helped in the process of correlation between sample and data obtained. Theoretical spectra have been corrected by a single scale factor of 0.961, and vibrational contributions by the molecular group were via VEDA software.

Analysis of the Ortho Effect: Basicity of 2-Substituted Benzonitriles

2006 ◽  
Vol 71 (8) ◽  
pp. 1239-1255 ◽  
Author(s):  
Otto Exner ◽  
Stanislav Böhm
Keyword(s):  
Density Functional ◽  
Substituent Effects ◽  
Small Dimension ◽  
Isodesmic Reactions ◽  
Ortho Effect ◽  
Weak Hydrogen Bonds ◽  
Protonated Forms ◽  
The Difference ◽  
Substituted Benzoic Acids ◽  
The One

Energies of 18 ortho-substituted benzonitriles and their protonated forms were calculated within the framework of the density functional theory at the level B3LYP/6-311+G(d,p). The substituent effects were evaluated in terms of isodesmic reactions as the effects on the basicity on the one hand and separately in the nitrile molecules and in the cations on the other. The ortho effect was defined as the difference when compared to the 4-substituted isomers. It is smaller than in the case of ortho-substituted benzoic acids but not negligible (up to 25 kJ mol-1). In unprotonated molecules it may be classified as purely steric effect, in spite of the small dimension of the CN group and estimates made with the calotte models. In the protonated forms, polar properties of the substituent are decisive. In addition, a new, quite important substituent effect was discovered with the substituents OH, SH, CHO and COOCH3, which is controlled by different conformation of protonated and unprotonated molecules. Substituents OH, SH and NH2 form also weak hydrogen bonds in unprotonated nitriles. In summary, 2-substituted benzonitriles allowed evaluating of several, partly new substituent effects but cannot serve as model molecules without an ortho effect, although the constant functional group CN is sterically little pretentious.

scholarly journals The Role of Through-Bond Stereoelectronic Effects in the Reactivity of 3-Azabicyclo[3.3.1]nonanes

2021 ◽  
Author(s):  
Croix Laconsay ◽  
Tyler Rho ◽  
Dean Tantillo
Keyword(s):  
Density Functional Theory ◽  
Hydrochloric Acid ◽  
Density Functional ◽  
Noncovalent Interactions ◽  
Substituent Effects ◽  
Isodesmic Reactions ◽  
Functional Theory ◽  
Stereoelectronic Effects ◽  
Computational Analyses

Hyperconjugation/conjugation through-bond stereoelectronic effects were studied with density functional theory (DFT) in the context of 3-azabicyclo[3.3.1]nonanes to unravel puzzling differences in reactivity between a vinylogous chloride (4) and a vinylogous ester (5). These compounds—whose structures differ only by one substituent—were found to display strikingly different reactivities in hydrochloric acid by Risch and co-workers (J. Am. Chem. Soc. 1991, 113, 9411–9412). Computational analyses of substituent effects, noncovalent interactions, natural bond orbitals, isodesmic reactions, and hydration propensities lead to a model for which the role of remote, through-bond stereoelectronic effects is key to explaining 4 and 5’s diverging reactivity.

scholarly journals 2-Nitro- and 4-fluorocinnamaldehyde based receptors as naked-eye chemosensors to potential molecular keypad lock

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Muhammad Islam ◽  
Zahid Shafiq ◽  
Fazal Mabood ◽  
Hakikulla H. Shah ◽  
Vandita Singh ◽  
...  
Keyword(s):  
Density Functional ◽  
Anion Recognition ◽  
Principal Component ◽  
Pattern Discrimination ◽  
Cost Effective ◽  
Pattern Generation ◽  
Naked Eye ◽  
The Density Functional Theory ◽  
Chemical Inputs ◽  
New Generation

AbstractNew-generation chemosensors desire small organic molecules that are easy to synthesise and cost-effective. As a new interdisciplinary area of research, the integration of these chemosensors into keypad locks or other advanced communication protocols is becoming increasingly popular. Our lab has developed new chemosensor probes that contain 2-nitro- (1–3) and 4-fluoro-cinnamaldehyde (4–6) and applied them to the anion recognition and sensing process. Probes 1–6 are colorimetric sensors for naked-eye detection of AcO−/CN−/F−, while probes 4–6 could differentiate between F− and AcO−/CN− anions in acetonitrile. Using the density functional theory (DFT), it was found that probes 1–6 acted as effective chemosensors. By using Probe 5 as a chemosensor, we explored colorimetric recognition of multiple anions in more detail. Probe 5 was tested in combination with a combinatorial approach to demonstrate pattern-generation capability and its ability to distinguish among chemical inputs based on concentration. After pattern discrimination using principal component analysis (PCA), we examined anion selectivity using DFT computation. In our study, probe 5 demonstrates excellent performance as a chemosensor and shows promise as a future molecular-level keypad lock system.

Influence of the variation in the Hubbard parameter (U) on activation energies of CeO2-catalysed reactions

2020 ◽  
Vol 98 (4) ◽  
pp. 385-389 ◽  
Author(s):  
Hussein A. Miran ◽  
Mohammednoor Altarawneh ◽  
Zainab N. Jaf ◽  
M. Mahbubur Rahman ◽  
Mansour H. Almatarneh ◽  
...  
Keyword(s):  
Density Functional ◽  
Strongly Correlated ◽  
Kinetics Parameters ◽  
Kinetics Modelling ◽  
The Density Functional Theory ◽  
Daunting Task ◽  
Structural And Electronic Properties ◽  
U Value ◽  
Hubbard Parameter ◽  
Reaction Energies

Accurate description of thermodynamic, structural, and electronic properties for bulk and surfaces of ceria (CeO2) necessitates the inclusion of the Hubbard parameter (U) in the density functional theory (DFT) calculations to precisely account for the strongly correlated 4f electrons. Such treatment is a daunting task when attempting to draw a potential energy surface for CeO2-catalyzed reaction. This is due to the inconsistent change in thermo-kinetics parameters of the reaction in reference to the variation in the U values. As an illustrative example, we investigate herein the discrepancy in activation and reaction energies for steps underlying the partial and full hydrogenation of acetylene over the CeO2(111) surface. Overall, we find that both activation and reaction energies positively correlate with the increase in the U value. In addition to benchmarking against more accurate theoretical methodologies, we suggest that U values are better optimized against kinetics modelling of experimentally observed profiles of products from the catalytic-assisted system of reactions.

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