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 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.

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>

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.

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>

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.

Use of a Lyophilized Reference Plasma to Compare Coagulation Test Procedures

1975 ◽  
Vol 34 (02) ◽  
pp. 426-444 ◽  
Author(s):  
J Kahan ◽  
I Nohén
Keyword(s):  
Oral Anticoagulant Therapy ◽  
Repeated Measurements ◽  
Test Procedures ◽  
Coagulation Activity ◽  
Close Relationship ◽  
Measured Activity ◽  
Test Materials ◽  
The Difference ◽  
The Stability ◽  
The One

SummaryIn 4 collaborative trials, involving a varying number of hospital laboratories in the Stockholm area, the coagulation activity of different test materials was estimated with the one-stage prothrombin tests routinely used in the laboratories, viz. Normotest, Simplastin-A and Thrombotest. The test materials included different batches of a lyophilized reference plasma, deep-frozen specimens of diluted and undiluted normal plasmas, and fresh and deep-frozen specimens from patients on long-term oral anticoagulant therapy.Although a close relationship was found between different methods, Simplastin-A gave consistently lower values than Normotest, the difference being proportional to the estimated activity. The discrepancy was of about the same magnitude on all the test materials, and was probably due to a divergence between the manufacturers’ procedures used to set “normal percentage activity”, as well as to a varying ratio of measured activity to plasma concentration. The extent of discrepancy may vary with the batch-to-batch variation of thromboplastin reagents.The close agreement between results obtained on different test materials suggests that the investigated reference plasma could be used to calibrate the examined thromboplastin reagents, and to compare the degree of hypocoagulability estimated by the examined PIVKA-insensitive thromboplastin reagents.The assigned coagulation activity of different batches of the reference plasma agreed closely with experimentally obtained values. The stability of supplied batches was satisfactory as judged from the reproducibility of repeated measurements. The variability of test procedures was approximately the same on different test materials.

Structure, Stability and Water Adsorption on Ultra-Thin TiO2 Supported on TiN

2019 ◽  
Author(s):  
Jose Julio Gutierrez Moreno ◽  
Marco Fronzi ◽  
Pierre Lovera ◽  
alan O'Riordan ◽  
Mike J Ford ◽  
...  
Keyword(s):  
Density Functional ◽  
Water Adsorption ◽  
Chemical Potential ◽  
Energy Gap ◽  
Molecular Water ◽  
Structure Stability ◽  
Ambient Conditions ◽  
Rutile Structure ◽  
The Stability ◽  
The One

<p></p><p>Interfacial metal-oxide systems with ultrathin oxide layers are of high interest for their use in catalysis. In this study, we present a density functional theory (DFT) investigation of the structure of ultrathin rutile layers (one and two TiO<sub>2</sub> layers) supported on TiN and the stability of water on these interfacial structures. The rutile layers are stabilized on the TiN surface through the formation of interfacial Ti–O bonds. Charge transfer from the TiN substrate leads to the formation of reduced Ti<sup>3+</sup> cations in TiO<sub>2.</sub> The structure of the one-layer oxide slab is strongly distorted at the interface, while the thicker TiO<sub>2</sub> layer preserves the rutile structure. The energy cost for the formation of a single O vacancy in the one-layer oxide slab is only 0.5 eV with respect to the ideal interface. For the two-layer oxide slab, the introduction of several vacancies in an already non-stoichiometric system becomes progressively more favourable, which indicates the stability of the highly non-stoichiometric interfaces. Isolated water molecules dissociate when adsorbed at the TiO<sub>2</sub> layers. At higher coverages the preference is for molecular water adsorption. Our ab initio thermodynamics calculations show the fully water covered stoichiometric models as the most stable structure at typical ambient conditions. Interfacial models with multiple vacancies are most stable at low (reducing) oxygen chemical potential values. A water monolayer adsorbs dissociatively on the highly distorted 2-layer TiO<sub>1.75</sub>-TiN interface, where the Ti<sup>3+</sup> states lying above the top of the valence band contribute to a significant reduction of the energy gap compared to the stoichiometric TiO<sub>2</sub>-TiN model. Our results provide a guide for the design of novel interfacial systems containing ultrathin TiO<sub>2</sub> with potential application as photocatalytic water splitting devices.</p><p></p>

The Demand For Money in Pakistan: Reply (Notes and Comments)

1975 ◽  
Vol 14 (3) ◽  
pp. 370-375
Author(s):  
M. A. Akhtar
Keyword(s):  
Interest Rates ◽  
Money Demand ◽  
Strong Support ◽  
Physical Capital ◽  
Careful Examination ◽  
Demand For Money ◽  
Weak Support ◽  
Complementarity Hypothesis ◽  
The Difference ◽  
The One

I am grateful to Abe, Fry, Min, Vongvipanond, and Yu (hereafter re¬ferred to as AFMVY) [1] for obliging me to reconsider my article [2] on the demand for money in Pakistan. Upon careful examination, I find that the AFMVY results are, in parts, misleading and that, on the whole, they add very little to those provided in my study. Nevertheless, the present exercise as well as the one by AFMVY is useful in that it furnishes us with an opportunity to view some of the fundamental problems involved in an empi¬rical analysis of the demand for money function in Pakistan. Based on their elaborate critique, AFMVY reformulate the two hypo¬theses—the substitution hypothesis and the complementarity hypothesis— underlying my study and provide us with some alternative estimates of the demand for money in Pakistan. Briefly their results, like those in my study, indicate that income and interest rates are important in deter¬mining the demand for money. However, unlike my results, they also suggest that the price variable is a highly significant determinant of the money demand function. Furthermore, while I found only a weak support for the complementarity between money demand and physical capital, the results obtained by AFMVY appear to yield a strong support for that rela¬tionship.1 The difference in results is only a natural consequence of alter¬native specifications of the theory and, therefore, I propose to devote most of this reply to the criticisms raised by AFMVY and the resulting reformulation of the two mypotheses.

Effect of leakage and blockage on the acoustic behavior of particle filters

2019 ◽  
Vol 67 (6) ◽  
pp. 483-492
Author(s):  
Seonghyeon Baek ◽  
Iljae Lee
Keyword(s):  
Transfer Matrix ◽  
Particle Filters ◽  
Acoustic Analysis ◽  
Transmission Loss ◽  
One Dimensional ◽  
Filter System ◽  
The Difference ◽  
The One ◽  
Analytical Approaches ◽  
Good Agreement

The effects of leakage and blockage on the acoustic performance of particle filters have been examined by using one-dimensional acoustic analysis and experimental methods. First, the transfer matrix of a filter system connected to inlet and outlet pipes with conical sections is measured using a two-load method. Then, the transfer matrix of a particle filter only is extracted from the experiments by applying inverse matrices of the conical sections. In the analytical approaches, the one-dimensional acoustic model for the leakage between the filter and the housing is developed. The predicted transmission loss shows a good agreement with the experimental results. Compared to the baseline, the leakage between the filter and housing increases transmission loss at a certain frequency and its harmonics. In addition, the transmission loss for the system with a partially blocked filter is measured. The blockage of the filter also increases the transmission loss at higher frequencies. For the simplicity of experiments to identify the leakage and blockage, the reflection coefficients at the inlet of the filter system have been measured using two different downstream conditions: open pipe and highly absorptive terminations. The experiments show that with highly absorptive terminations, it is easier to see the difference between the baseline and the defects.

Development and Validation of Spectrophotometric and Liquid Chromatographic Methods for Estimation of Tigecycline in Injections

2020 ◽  
Vol 13 (5) ◽  
pp. 5148-5154
Author(s):  
Sagar Suman Panda ◽  
Ravi Kumar B.V.V.
Keyword(s):  
Area Under The Curve ◽  
Reversed Phase ◽  
Equal Concentration ◽  
Pharmaceutical Dosage Form ◽  
Liquid Chromatographic Method ◽  
Array Detection ◽  
The Difference ◽  
The One ◽  
Development And Validation ◽  
Liquid Chromatographic

Three new analytical methods were optimized and validated for the estimation of tigecycline (TGN) in its injection formulation. A difference UV spectroscopic, an area under the curve (AUC), and an ultrafast liquid chromatographic (UFLC) method were optimized for this purpose. The difference spectrophotometric method relied on the measurement of amplitude when equal concentration solutions of TGN in HCl are scanned against TGN in NaOH as reference. The measurements were done at 340 nm (maxima) and 410nm (minima). Further, the AUC under both the maxima and minima were measured at 335-345nm and 405-415nm, respectively. The liquid chromatographic method utilized a reversed-phase column (150mm×4.6mm, 5µm) with a mobile phase of methanol: 0.01M KH2PO4 buffer pH 3.5 (using orthophosphoric acid) in the ratio 80:20 %, v/v. The flow rate was 1.0ml/min, and diode array detection was done at 349nm. TGN eluted at 1.656min. All the methods were validated for linearity, precision, accuracy, stability, and robustness. The developed methods produced validation results within the satisfactory limits of ICH guidance. Further, these methods were applied to estimate the amount of TGN present in commercial lyophilized injection formulations, and the results were compared using the One-Way ANOVA test. Overall, the methods are rapid, simple, and reliable for routine quality control of TGN in the bulk and pharmaceutical dosage form. 

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