Isodesmic Reaction

2016 ◽  
Author(s):  
Vladimir I. Minkin
Keyword(s):  
Isodesmic Reaction

scholarly journals Large Stabilization Effects by Intramolecular Beryllium Bonds in Ortho-Benzene Derivatives

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3401
Author(s):  
Tsai I-Ting ◽  
M. Merced Montero-Campillo ◽  
Ibon Alkorta ◽  
José Elguero ◽  
Manuel Yáñez
Keyword(s):  
Reaction Scheme ◽  
Binding Energies ◽  
Intramolecular Interactions ◽  
Isodesmic Reaction ◽  
Bond Critical Point ◽  
Interaction Energies ◽  
Benzene Derivatives ◽  
Covalent Interaction ◽  
Beryllium Bond ◽  
Donor And Acceptor

Intramolecular interactions are shown to be key for favoring a given structure in systems with a variety of conformers. In ortho-substituted benzene derivatives including a beryllium moiety, beryllium bonds provide very large stabilizations with respect to non-bound conformers and enthalpy differences above one hundred kJ·mol−1 are found in the most favorable cases, especially if the newly formed rings are five or six-membered heterocycles. These values are in general significantly larger than hydrogen bonds in 1,2-dihidroxybenzene. Conformers stabilized by a beryllium bond exhibit the typical features of this non-covalent interaction, such as the presence of a bond critical point according to the topology of the electron density, positive Laplacian values, significant geometrical distortions and strong interaction energies between the donor and acceptor quantified by using the Natural Bond Orbital approach. An isodesmic reaction scheme is used as a tool to measure the strength of the beryllium bond in these systems in terms of isodesmic energies (analogous to binding energies), interaction energies and deformation energies. This approach shows that a huge amount of energy is spent on deforming the donor–acceptor pairs to form the new rings.

Anomalous stabilizing and destabilizing effects in some cyclic π-electron systems

1993 ◽  
Vol 71 (8) ◽  
pp. 1123-1127 ◽  
Author(s):  
Peter Politzer ◽  
M. Edward Grice ◽  
Jane S. Murray ◽  
Jorge M. Seminario
Keyword(s):  
Ab Initio ◽  
Lone Pair ◽  
Electrostatic Potentials ◽  
Electron Delocalization ◽  
Isodesmic Reaction ◽  
Computational Studies ◽  
Electron Systems ◽  
Molecular Electrostatic Potentials ◽  
Lone Pairs

Ab initio computational studies have been carried out for three molecules that are commonly classed as antiaromatic: cyclobutadiene (1), 1,3-diazacyclobutadiene (7), and 1,4-dihydropyrazine (6). Their dinitro and diamino derivatives were also investigated. Stabilizing or destabilizing energetic effects were quantified by means of the isodesmic reaction procedure at the MP2/6-31G*//HF/3-21G level, and calculated molecular electrostatic potentials (HF/STO-5G//HF/3-21G) were used as a probe of electron delocalization. Our results do not show extensive delocalization in the π systems of any one of the three parent molecules. The destabilization found for 1 and 7 is attributed primarily to strain and to repulsion between the localized π electrons in the C=C and C=N bonds, respectively. However, 6 is significantly stabilized, presumably due to limited delocalization of the nitrogen lone pairs. NH2 groups are highly stabilizing, apparently because of lone pair delocalization. NO2 is neither uniformly stabilizing nor destabilizing.

scholarly journals Standard Molar Enthalpies of Formation of Halomethanes Based on Quantum Chemical Computations

2020 ◽  
Author(s):  
Konstantinos Kalamatianos
Keyword(s):  
Gas Phase ◽  
Quantum Chemical ◽  
Halogen Bond ◽  
Chemical Processes ◽  
Enthalpies Of Formation ◽  
Isodesmic Reaction ◽  
Gold Standard Method ◽  
Ozone Destruction ◽  
Quantum Chemical Computations ◽  
Reaction Schemes

Accurate calculations of standard molar enthalpies of formation (ΔΗf°)m(g) and carbon-halogen bond dissociation enthalpies, BDE, of a variety of halomethanes with relevance on several atmospheric chemical processes and particularly to ozone destruction, were performed in the gas phase at 298.15 K. The (ΔΗf°)m(g) of the radicals formed through bond dissociations have also been computed. Ab initio computational methods and isodesmic reaction schemes were used. It is found that for the large majority of these species, the gold standard method of quantum chemistry (CCSD(T)) and even MP2 are capable to predict enthalpy values nearing chemical accuracy provided that isodesmic reaction schemes are used. New estimates for standard molar enthalpies of formation and BDE are suggested including for species that to our knowledge there are no experimental (ΔΗf°)m(g) (CHCl2Br, CHBr2Cl, CHBrCl, CHICl, CHIBr) or BDE values (CHCl2Br, CHBr2Cl, CHBrCl, CHICl, CHIBr) available in the literature. The method and calculational procedures presented may profitably be used to obtain accurate (ΔΗf°)m(g) and BDE values for these species.

Attenuation of the Substituent Effects Along the Aliphatic Chain

2004 ◽  
Vol 69 (5) ◽  
pp. 984-995 ◽  
Author(s):  
Stanislav Böhm ◽  
Otto Exner
Keyword(s):  
Functional Group ◽  
Inductive Effect ◽  
Substituent Effects ◽  
Transmission Factor ◽  
Isodesmic Reaction ◽  
Aliphatic Chain ◽  
Model Compounds ◽  
Derivatives Of ◽  
Methylene Group ◽  
Isolated Molecules

Two series of model compounds were devised to follow the attenuation of substituent effects with an interposed methylene group: short-chain aliphatic compounds 1 and derivatives of bicyclo[2.2.2]octane 5. In all compounds, chlorine atom acts as substituent and charged oxygen atom as the functional group; the interaction of both is measured by the reaction energy of the isodesmic reaction calculated at the B3LYP/AUG-cc-pVTZ//B3LYP/6-311+G(d,p) and/or B3LYP/6-311+G(d,p) levels. Attenuation of the substituent inductive effect with the distance is less steep than observed previously in solution. It depends also markedly on the conformation but cannot be reproduced, not even approximately, by the electrostatic formula. Only for simple regular conformations, it can be described approximately by an exponential function with the transmission factor for one methylene group equal to 0.74. The behavior of isolated molecules differs in this case distinctly from the reactivity in solution. Nevertheless, the significance of the two formulas, electrostatic and exponential, is similar in the isolated molecules and in solution. These formulas represent only two different, rather crude mathematical approximations and cannot be given any physical meaning.

Isodesmic reaction for accurate theoretical pKa calculations of amino acids and peptides

2016 ◽  
Vol 18 (16) ◽  
pp. 11202-11212 ◽  
Author(s):  
S. Sastre ◽  
R. Casasnovas ◽  
F. Muñoz ◽  
J. Frau
Keyword(s):  
Amino Acids ◽  
Computational Chemistry ◽  
Computational Cost ◽  
Quantitative Prediction ◽  
Isodesmic Reaction ◽  
Pka Calculations ◽  
Current Challenge ◽  
Low Computational Cost ◽  
A Current

Theoretical and quantitative prediction of pKa values at low computational cost is a current challenge in computational chemistry.

scholarly journals Prediction of pKa values for drug-like molecules using semiempirical quantum chemical methods

2016 ◽  
Author(s):  
Jan H. Jensen
Keyword(s):  
Proton Transfer ◽  
Prediction Method ◽  
Isodesmic Reaction ◽  
Pka Values ◽  
Pka Prediction ◽  
Quantum Chemical Methods ◽  
Pka Value ◽  
Amine Groups ◽  
Computational Resources ◽  
Better Than

Rapid yet accurate pKa prediction for drug-like molecules is a key challenge in computational chemistry. This study uses PM6-DH+/COSMO, PM6/COSMO, PM7/COSMO, PM3/COSMO, AM1/COSMO, PM3/SMD, AM1/SMD, and DFTB3/SMD to predict the pKa values of 53 amine groups in 48 drug-like compounds. The approach uses an isodesmic reaction where the pKa value is computed relative to a chemically related reference compound for which the pKa value has been measured experimentally or estimated using a standard empirical approach. The AM1- and PM3-based methods perform best with RMSE values of 1.4 - 1.6 pH units that have uncertainties of ±0.2-0.3 pH units, which make them statistically equivalent. However, for all but PM3/SMD and AM1/SMD the RMSEs are dominated by a single outlier, cefadoxil, caused by proton transfer in the zwitterionic protonation state. If this outlier is removed, the RMSE values for PM3/COSMO and AM1/COSMO drop to 1.0 ± 0.2 and 1.1 ± 0.3, while PM3/SMD and AM1/SMD remain at 1.5 ± 0.3 and 1.6 ± 0.3/0.4 pH units, making the COSMO-based predictions statistically better than the SMD-based predictions. So for pKa calculations where a zwitterionic state is not involved or proton transfer in a zwitterionic state is not observed then PM3/COSMO or AM1/COSMO is the best pKa prediction method, otherwise PM3/SMD or AM1/SMD should be used. Thus, fast and relatively accurate pKa prediction for 100-1000s of drug-line amines is feasible with the current setup and relatively modest computational resources.

Isodesmic reaction energies and the relative acidities of carboxylic acids and alcohols

1988 ◽  
Vol 53 (8) ◽  
pp. 1812-1815 ◽  
Author(s):  
T. Darrah Thomas ◽  
Thomas X. Carroll ◽  
Michele R. F. Siggel
Keyword(s):  
Carboxylic Acids ◽  
Isodesmic Reaction ◽  
Reaction Energies

Theoretical Studies on an Energetic Material: Di-s-Tetrazine Derivatives

2014 ◽  
Vol 1058 ◽  
pp. 122-126 ◽  
Author(s):  
Hua Zhou ◽  
Zhong Liang Ma ◽  
Jia Hu Guo ◽  
Jian Long Wang
Keyword(s):  
Density Functional ◽  
Energetic Material ◽  
Dft Method ◽  
High Energy ◽  
Heat Of Formation ◽  
High Energy Density ◽  
Detonation Performance ◽  
Isodesmic Reaction ◽  
Functional Theory ◽  
Calculated Density

Computations by density functional theory (DFT) method were performed on a series of di-s-tetrazine derivatives with different substituents and linkages. The heat of formation (HOF) was predicted by designed isodesmic reaction. The results illustrated that introductions group –N3or –N=N– could augment the HOF extremely. The crystal structures were obtained by molecular mechanics methods with dreiding force field. Detonation performance was evaluated by using the Kamlet-Jacobs based on the calculated density and HOF. It was found that –ONO2, –NF2, –NH–NH– and –N=N– groups were effective to enhance the detonation performance of these derivatives. Seven compounds were screened as the potential candidates for high energy density materials.

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