G3MP2B3 Level Of Theory Research Articles

Thermochemistry of C7H16 to C10H22 alkane isomers: primary, secondary, and tertiary C-H bond dissociation energies and effects of branching.

Standard enthalpies of formation (ΔH°f298) of methyl, ethyl, primary and secondary propyl, and n-butyl radicals are evaluated and used in work reactions to determine internal consistency. They are then used to calculate the enthalpy of formation for the tert-butyl radical. Other thermochemical properties including standard entropies (S°(T)), heat capacities (Cp(T)), and carbon-hydrogen bond dissociation energies (C-H BDEs) are reported for n-pentane, n-heptane, 2-methylhexane, 2,3-dimethylpentane, and several branched higher carbon number alkanes and their radicals. ΔH°f298 and C-H BDEs are calculated using isodesmic work reactions at the B3LYP (6-31G(d,p) and 6-311G(2d,2p) basis sets), CBS-QB3, CBS-APNO, and G3MP2B3 levels of theory. Structures, moments of inertia, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level for contributions to entropy and heat capacities. Enthalpy calculations for these hydrocarbon radical species are shown to have consistency with the CBS-QB3 and CBS-APNO methods using all work reactions. Our recommended ideal gas phase ΔH°f298 values are from the average of all CBS-QB3, CBS-APNO, and for G3MP2B3, only where the reference and target radical are identical types, and are compared with literature values. Calculated values show agreement between the composite calculation methods and the different work reactions. Secondary and tertiary C-H bonds in the more highly branched alkanes are shown to have bond energies that are several kcal mol(-1) lower than the BDEs in corresponding smaller molecules often used as reference species. Entropies and heat capacities are calculated and compared to literature values (when available) when all internal rotors are considered.

Mechanistic Study of the Deamidation Reaction of Glutamine: A Computational Approach

Glutamine--a popular nutritional supplement, non-toxic amino acid, and an essential interorgan and intercellular ammonia transporter--can destroy the neurons' mitochondria. When glutamine enters (like a Trojan horse) into the mitochondria, in the presence of glutaminase, it reacts with water and yields glutamate and excess ammonia which opens gates in the membrane of the mitochondria and thereby destroys it. The mechanistic details underlying the molecular basis of the catabolic production of excess ammonia remain unclear. In the present paper, both 5-oxoproline-mediated and direct pathways for glutamine deamidation are studied using wave function and density functional theories. The mechanisms are studied both in the gas phase and in aqueous solution using the polarizable continuum model (PCM) and solvent model on density (SMD) solvation models. Among three glutamine deamidation pathways, a two-step pathway, GDB, shows the lowest gas phase barrier height of 189 kJ/mol with the G3MP2B3 level of theory. Incorporation of solvent through PCM and SMD models reduces the barrier height to 183 and 174 kJ/mol, respectively. For the hydrolysis of 5-oxoproline, a two-step mechanism, pathway PH-B, provides a lower gas phase energy barrier (187 kJ/mol) compared to one-step (201 kJ/mol) and three-step (227 kJ/mol) pathways at G3MP2B3. Although direct hydrolysis with OH(-), pathway DHE, has the lowest gas phase barrier of 135 kJ/mol, the solvent has little effect on the barrier. For the direct hydrolysis with OH(-)/H2O, pathway DHF, the overall barrier is 143 kJ/mol, in the gas phase at G3MP2B3. In aqueous solution, the overall barrier decreases to 76 and 75 kJ/mol with PCM and SMD, respectively, at B3LYP/6-31+G(d,p), making this the most plausible mechanism. Compared to PCM, SMD predicts lower barriers for nearly all pathways investigated.

Comparative computational investigation of the reaction mechanism for the hydrolytic deamination of cytosine, cytosine butane dimer and 5,6-saturated cytosine analogues

A detailed computational investigation of the mechanism for the hydrolytic deamination of cytosine, its cyclobutane cytosine dimer CC, and other 5,6-saturated cytosine analogues was undertaken. The rationale behind this work was twofold: to clearly establish the mechanism for the hydrolytic deamination of cytosine and cytosine analogues by comparing calculated and experimentally known activation energies and secondly, to provide a logical basis for the much lower activation energy barriers for 5,6-saturated cytosine analogues versus cytosine monomer.Energies for all relevant species including intermediates and transition states for all pathways studied were determined using B3LYP/6-31G(d,p), B3LYP/6-31+G(d,p) and G3MP2B3 levels of theory and solvent calculations were performed using both the polarizable continuum model (PCM) and the solvation model on density (SMD). Activation energies, Gibbs energies of activation, ΔH of reaction and ΔG of reaction were calculated for each pathway investigated. Deformation energies as well as the total interaction energy of reactant species were determined for the formation of the key transition state (TS2) which decomposes to form a tetrahedral intermediate in all pathways studied.The overall gas phase activation energies found for the deamination of cytosine and dicytosine with three explicit water molecules are in good agreement with the experimental values found in the literature. Such good agreement between calculated and experimental results is very strong evidence that the mechanism for the hydrolytic deamination has been correctly determined. Reduced deformation energy required to form the key transition state TS2 for the C5–C6 saturated cytosine analogues has been found to be the main reason for the significantly lower activation energies for their hydrolytic deamination.

Experimental and computational study of the energetics of hydantoin and 2-thiohydantoin

This work reports an experimental and a theoretical study of two imidazolidine derivatives, hydantoin (CAS No. 461-72-3) and 2-thiohydantoin (CAS No. 503-87-7).The standard (p°=0.1MPa) molar energies of combustion of hydantoin and 2-thiohydantoin were measured by static and rotating bomb combustion calorimetry, respectively. The standard molar enthalpies of sublimation, at T=298.15K, were derived from the temperature dependence of the vapour pressures of these compounds, measured by the Knudsen-effusion technique, and from high temperature Calvet microcalorimetry. The conjugation of these experimental results enables the calculation of the standard molar enthalpies of formation in the gaseous state, at T=298.15K, which are discussed in terms of structural contributions.We have also estimated the gas-phase enthalpy of formation from high-level ab initio molecular orbital calculations at the G3MP2B3 level of theory, being the computed values in good agreement with the experimental ones. Furthermore, this composite approach was also used to obtain information about the gas-phase basicities, proton and electron affinities and adiabatic ionization enthalpies.

Thermochemistry and Bond Dissociation Energies of Ketones

Ketones are a major class of organic chemicals and solvents, which contribute to hydrocarbon sources in the atmosphere, and are important intermediates in the oxidation and combustion of hydrocarbons and biofuels. Their stability, thermochemical properties, and chemical kinetics are important to understanding their reaction paths and their role as intermediates in combustion processes and in atmospheric chemistry. In this study, enthalpies (ΔH°(f 298)), entropies (S°(T)), heat capacities (C(p)°(T)), and internal rotor potentials are reported for 2-butanone, 3-pentanone, 2-pentanone, 3-methyl-2-butanone, and 2-methyl-3-pentanone, and their radicals corresponding to loss of hydrogen atoms. A detailed evaluation of the carbon-hydrogen bond dissociation energies (C-H BDEs) is also performed for the parent ketones for the first time. Standard enthalpies of formation and bond energies are calculated at the B3LYP/6-31G(d,p), B3LYP/6-311G(2d,2p), CBS-QB3, and G3MP2B3 levels of theory using isodesmic reactions to minimize calculation errors. Structures, moments of inertia, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) density functional level and are used to determine the entropies and heat capacities. The recommended ideal gas-phase ΔH°(f 298), from the average of the CBS-QB3 and G3MP2B3 levels of theory, as well as the calculated values for entropy and heat capacity are shown to compare well with the available experimental data for the parent ketones. Bond energies for primary, secondary, and tertiary radicals are determined; here, we find the C-H BDEs on carbons in the α position to the ketone group decrease significantly with increasing substitution on these α carbons. Group additivity and hydrogen-bond increment values for these ketone radicals are also determined.

Energetic Study Applied to the Knowledge of the Structural and Electronic Properties of Monofluorobenzonitriles

The present work reports an energetic and structural study of 2-fluoro-, 3-fluoro-, and 4-fluorobenzonitrile. The standard molar enthalpies of formation, in the condensed phase, of the three isomers were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K. The standard molar enthalpies of vaporization or sublimation (for 4-fluorobenzonitrile), at T = 298.15 K, were measured using high-temperature Calvet microcalorimetry. The combination of these two parameters yields the standard molar enthalpies of formation in the gaseous phase. The vapor-pressure study of the referred compounds was performed by a static method, and the enthalpies of phase transition derived from the application of the Clarke and Glew equation. Theoretically estimated gas-phase enthalpies of formation, basicities, proton and electron affinities, and adiabatic ionization enthalpies were calculated from the G3MP2B3 level of theory. In order to evaluate the electronic properties, the geometries were reoptimized at MP2/cc-pVTZ level, and the QTAIM and NICS were computed. On the basis of the donor-acceptor system, another approach for evaluating the electronic effect for these compounds, using the NBO is suggested. The UV-vis spectroscopy study for the three isomers was performed. The intensities and the band positions were correlated with the thermodynamic properties calculated computationally.

Isomerization and Dissociation of n-Butylbenzene Radical Cation

Fragmentation mechanisms of ionized butylbenzene to give m/z 91 and m/z 92 fragment ions have been examined at the G3B3 and G3MP2B3 levels of theory. It is shown that the energetically favored pathways lead to tropylium, Tr(+), and methylene-2,4-cyclohexadiene, MCD(•+), ions. Formation of m/z 91 benzyl ions, Bz(+), by a simple bond fission (SBF) process, needs about 30 kJ/mol more energy than Tr(+). Possible formation of C(7)H(8)(•+) ions of structures different from the retro-ene rearrangement (RER) product, MCD(•+), has been also considered. Comparison with experimental data of this "thermometer" system is done through a kinetic modeling using Rice-Ramsperger-Kassel-Marcus (RRKM) and orbiting transition state (OTS) rate constant calculations on the G3MP2B3 0 K energy surface. The results agree with previous experimental observation if (i) the competitive formation of Tr(+) and Bz(+) is taken into account in the m/z 91 pathway, and (ii) the stepwise character of the RER fragmentation is introduced in the m/z 92 fragmentation route.

Theoretical investigation of the conformational intricacies and thermodynamic functions of noradrenaline

Noradrenaline is a neurotransmitter that is involved in various psychological processes. In the neurotransmission process, noradrenaline binds to an adrenergic receptor by forming a complex of hydrogen bonds between its two catechol ring hydroxyl groups and the amino acid residues of adrenergic receptors. Although the two catechol ring hydroxyl groups play a crucial role in making hydrogen bonds to the binding site of the adrenergic receptor, the contribution of the catechol ring hydroxyl groups to the intramolecular stability that may affect docking has not been fully studied. To reveal the specific role that the catechol ring hydroxyl groups might play in stabilizing noradrenaline, the quantum chemical computations of geometry optimization and thermodynamic functions of N-protonated noradrenaline conformers were performed at both the B3LYP/6–31G(d,p) and G3MP2B3 levels of theory, using the Gaussian 03 program. The results were compared with those of N-protonated β-hydroxy-β-phenylethylamine, which is identical to noradrenaline except it lacks two catechol ring hydroxyl groups. For the first time, post-Hartree–Fock computations were used to obtain thermodynamic functions to establish relative stabilities of all possible conformers of N-protonated noradrenaline. In this study, 18 distinct structures of N-protonated noradrenaline were revealed, and the catechol ring hydroxyl groups were found to affect noradrenaline stability positively or negatively depending on the conformational orientations. On the basis of available experimental results, the issue that the least stable conformation of two catechol ring hydroxyl groups may be involved in the docking process has been raised. These findings may be useful in synthesis of derivatives of noradrenaline in drug design.

Mechanistic Investigation on the Reaction of O− with CH3CN Using Density Functional Theory

The potential energy profile of the reaction between the atomic oxygen radical anion and acetonitrile has been mapped at the G3MP2B3 level of theory. Geometries of the reactants, products, intermediate complexes, and transition states involved in this reaction have been optimized at the (U)B3LYP/6-31+G(d,p) level, and then their accurate relative energies have been improved using the G3MP2B3 method. The potential energy profile is confirmed via intrinsic reaction coordinate calculations of transition states. Four possible production channels are examined respectively, as H+ transfer, H-atom transfer, H2+ transfer, and bi-molecular nucleophilic substitution (SN2) reaction pathways. Based on present calculations, the H2+ transfer reaction is major among these four channels, which agrees with previous experimental conclusions.

Influence of hydrogen bonding on hydrogen-atom abstraction reactions of dehydropyridinium cations in the gas phase.

The reactions of several substituted, positively charged dehydropyridinium cations with cyclohexane, methanol, and tetrahydrofuran have been examined in a Fourier-transform ion cyclotron resonance mass spectrometer. All of the charged monoradicals react with the neutral reagents exclusively via hydrogen atom abstraction. For cyclohexane, there is a good correlation between the reaction efficiencies and the calculated electron affinities at the radical sites; that is, the greater the electron affinity of the charged monoradical at the radical site, the faster the reaction. The reaction efficiencies with methanol and tetrahydrofuran, however, do not correlate with the calculated electron affinities. Density functional theory (DFT) calculations indicate that for these reagents a stabilizing hydrogen bonding interaction exists in the hydrogen atom abstraction transition states for some of the charged monoradicals but not for others. At both the MPW1K and G3MP2B3 levels of theory, there is a good correlation between the calculated activation enthalpies and the observed reaction efficiencies, although the G3MP2B3 method provides a slightly better correlation than the MPW1K method. The extent of enhancement in the reaction efficiencies caused by the hydrogen bonding interactions parallels the calculated hydrogen bond lengths in the transition states.

Theoretical investigation of the reaction mechanism of atomic oxygen radical anion with pyridine

The reaction mechanism of atomic oxygen radical anion (O −) with pyridine (C 5H 5N) has been investigated at the G3MP2B3 level of theory. Three different entrance potential energy surfaces are explored, respectively, as atomic oxygen radical anion attacks γ-, β- and α-H atoms of pyridine. Possible thermodynamic product channels are examined subsequently. Based on the calculated G3MP2B3 energies and optimized geometries of all species for the title reaction, it has been demonstrated that the oxide anion formation channel is dominant, and the C 5H 3N − + H 2O channel is also favorable in thermodynamics, whereas the H-abstraction and H +-abstraction channels are inaccessible at room temperature. The present conclusions are consistent qualitatively with the previous experimental results. The secondary reactions of the anionic products are expected to be responsible for the contradiction of branching ratios between present calculation and previous experiments.

Structure and Thermochemical Properties of 2-Methoxyfuran, 3-Methoxyfuran, and Their Carbon-Centered Radicals Using Computational Chemistry

Methoxyfurans are known components in a number of biofuel synthesis processes and their thermochemical properties are important to the stability, reaction paths, and chemical kinetics of these species. Enthalpies (DeltaH degrees (f298)), entropies (S degrees (298)), and heat capacities (C(p)(T)) are reported for 2-methoxyfuran and 3-methoxyfuran, cyclic ethers with possible biofuel implications, and their radicals corresponding to loss of hydrogen atoms. Standard enthalpies of formation are calculated at the B3LYP/6-31G(d,p), B3LYP/6-311G(2d,2p), CBS-QB3, G3MP2B3, and G3 levels of theory with isodesmic reactions to minimize calculation errors. Structures, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) density functional level and are used to determine the entropy and heat capacities. The recommended ideal gas phase enthalpy of formation, from the average of the CBS-QB3 and G3MP2B3 levels of theory, for 2-methoxyfuran is -45.0 kcal mol(-1) and for 3-methoxyfuran is -41.1 kcal mol(-1). Bond dissociation energies are also calculated. The C-H bonds of the furan ring are approximately 120 kcal mol(-1), which is consistent with recent data on several alkylfurans; they are significantly stronger than non-aromatic, stable heterocyclic structures. The bond energy decreases to 98 kcal mol(-1) for the methoxy-methyl C-H bonds making this methyl site a favorable abstraction target and an important site for initial decomposition paths during combustion. Group additivity for furan is discussed and groups for furan and methoxyfuran carbon radicals are derived.

Thermodynamic Role of Glutathione Oxidation by Peroxide and Peroxybicarbonate in the Prevention of Alzheimer’s Disease and Cancer

First principle quantum molecular computations have been carried out at the B3LYP/6-31G(d,p) and G3MP2B3 levels of theory on ethyl mercaptan and diethyl disulfide to study their full conformational space. The consequences of molecular axis chirality for the potential energy hypersurface of diethyl disulfide was fully explored. Thermodynamic functions (U, H, S, and G) have been computed for every conformer of the products as well as the reactants of the redox systems studied. Relative values of the thermodynamic functions were calculated with respect to the reference structures with anti orientation. The energetics of the following Red-Ox reactions Et-SH+HO-OH+HS-Et --> 2H2O+Et-S-S-Et Et-SH+HO-OCOO(-)+HS-Et --> H2O+Et-S-S-Et+HCO3- have been chosen to mimic the biologically important Red-Ox reactions of glutathione G-SH+H2O2+HS-G --> 2H2O+G-S-S-G G-SH+HCO4-+HS-G --> H2O+G-S-S-G+HCO3-. The Red-Ox reaction of Et-SH --> Et-S-S-Et was found to be exothermic by first principle molecular computations and the intramolecular interactions, such as the unusual C-H...H-C noncovalent bondings were studied by Bader's atoms in molecules analysis of the electron density topology. The present paper focuses attention on the thermodynamic aspect of the redox reaction of glutathione. It has been noted previously that on going from a cancerous to a healthy cell, the entropy change is negative, corresponding to information accumulation. Likewise, the dissociation of peptide parallel beta-sheets, that dominate the plaques in Alzheimer's Disease, governs negative entropy change. It may be interesting to note, according to the results obtained in the present paper, a negative entropy change, corresponding to information accumulation.

Thermodynamic Functions of Molecular Conformations of (2-Fluoro-2-phenyl-1-ethyl)ammonium Ion and (2-Hydroxy-2-phenyl-1-ethyl)ammonium Ion as Models for Protonated Noradrenaline and Adrenaline: First-Principles Computational Study of Conformations and Thermodynamic Functions for the Noradrenaline and Adrenaline Models

This paper reports the structural and thermodynamic consequences of substitution of the OH group by the isoelectronic F-atom in the case of the adrenaline family of molecules. The conformational landscapes were explored for the two enantiomeric forms of N-protonated-beta-fluoro-beta-phenyl-ethylamine, also called (2-fluoro-2-phenyl-1-ethyl)-ammonium ion (Model 1) and that of N-protonated-beta-hydroxy-beta-phenyl-ethylamine, also referred to as (2-hydroxy-2-phenyl-1-ethyl)-ammonium (Model 2) models of noradrenaline and adrenaline molecules. These full conformational studies were carried out by first principles of quantum mechanical computations at the B3LYP/6-31G(d,p) and G3MP2B3 levels of theory, using the Gaussian03 program. Also, frequency calculations of the stable structures were performed at the B3LYP/6-31G(d,p), and G3MP2B3 levels of theory. The thermodynamic functions (U, H, S, and G) of the various stable conformations of the title compounds were calculated at these levels of theory for the R and S stereoisomers. Relative values of the thermodynamic functions have been calculated with respect of the chosen reference conformers in which all relevant dihedral angles assumed anti orientation for the Model 1 and Model 2. Through the combination of both point and axis chirality, the enantiomeric and diastereomeric relationships of the six structures for each molecule investigated were established. Intramolecular hydrogen bonding interactions have been studied by the atoms in molecules (AIM) analysis of the electron density. The aromaticity of phenyl group has been determined by a selective hydrogenation protocol. The pattern of the extent of aromacity, due intramolecular interactions, varies very little between the two models studied.

Accurate micro- and macro- gas phase basicities of hydroxyl-radical-modified pyrimidines estimated by advanced quantum chemistry methods

The gas phase basicities (GPB) of 16 hydroxyl-radical-derived analogues of model pyrimidine nucleosides were analysed at B3LYP/aug-cc-pVDZ and G3MP2B3 levels of theory. All possible tautomeric equilibriums of neutral and protonated forms of pyrimidine analogues were taken into account. The oxidation of pyrimidines usually reduces the GPB values with respect to canonical values. The only exception was observed in the case of 5,6-dihydroxycytidine, which is more basic than model cytidine if both macro- and micro-scopic measures of basicities are used for comparison. In addition, 6-hydroxycytidine is characterised more by the basic character of the O2 atom compared to the more basic centre of cytidine, despite the fact that the GPB values of both these compounds are almost identical. Although the B3LYP/aug-cc-pVDZ approach seems to be an accurate and robust method for GPB estimation, the microscopic protonation properties are much more sensitive to this method since the difference in energy between some tautomers is often less than 1 kcal/mol with method-dependent succession. In such cases, G3MP2B3 is recommended.

An ab initio and density functional theory study on the mechanism for the reaction of OH with 2-ethylfuran

The mechanism of the reaction of OH + 2-ethylfuran has been investigated using the G3MP2 and G3MP2B3 levels of theory. The geometric parameters of all species involved in the reaction have been optimized at the MP2 and B3LYP levels of theory with 6-311G(d,p) basis set. The overall profile of doublet potential energy surface (PES) for the OH + 2-ethylfuran reaction has been constructed using the G3MP2 and G3MP2B3 methods. The results show that the addition-elimination mechanism dominates the OH + 2-ethylfuran reaction and the major products are CH3CH2C(OH)CHCHCHOH (P8) and CH3CH2COCHCHCHOH (P6).

Reaction Mechanism of Hydroxyl Anion with Benzene

The reaction mechanism of hydroxyl anion and benzene has been theoretically studied at the G3MP2B3 level of theory. All possible thermodynamic product channels are considered and investigated. The [C6H6…OH]- complex formation has been found on the most favorable reaction pathway, which is consistent with the previous experimental studies. The proton transfer and hydrogen replacement pathways are endothermic and difficult to occur in the case of the lower experimental collision energy. Additionally, the H2 formation as an exothermal product channel of this reaction system by -119.5 kJ·mol-1 hardly happens because of a high energy barrier. The proton transfer processes of hydroxyl anion, oxygen anion, and fluorine anion from benzene have been compared in the present computation, and the electron transfers in these processes were investigated by the Mulliken charge population analysis as well. Furthermore, the reaction mechanism between hydroxyl anion or hydroxyl radical and benzene, has been also compared and analyzed.

Transition State Infrared Spectra for the Trans→Cis Isomerization of a Simple Peptide Model

Trans-->cis isomerization of N-methylacetylamide (MeCO-NHMe) has been studied at the G3MP2B3 level of theory and the vibration spectrum has been calculated as a function of the torsional mode of motion along the peptide bond. Noticeable spectral differences have been observed for the transition state interconnecting the cis and trans isomers.

Ab initio study of the decomposition of formamidine

The decomposition of formamidine yielding hydrogen cyanide and ammonia has been investigated by ab initio calculations. Optimized geometries for reactants, transition states, and products were determined at the HF/6-31G(d) and MP2/6-31G(d) levels of theory. Energies were also determined at the G1, G2, G2MP2, G3, G3B3, G3MP2, and G3MP2B3 levels of theory. The role of water in the decomposition reaction of formamidine was examined. Intrinsic reaction coordinate (IRC) analysis was carried out for all transition states. Activation energies, enthalpies and free energies of activation were also calculated for each reaction pathway. G3 level of theory predicts the gas-phase decomposition of formamidine to have a high activation energy of 259.1 kJ mol–1. Adding one water molecule catalyses the reaction by forming a cyclic hydrogen-bonded transition state, reducing the barrier to 169.4 kJ mol–1 at the G3 level. Addition of a second water, which acts as a "solvent" molecule, further reduces the barrier to 151.1 kJ mol–1 at the G3 level. These values are still high and explain why rather extreme conditions are necessary to achieve this reaction experimentally. Thermodynamic properties (ΔE, ΔH, and ΔG) for each reaction pathway studied were also calculated. The G3 heats of reaction (ΔE) of the gas-phase decomposition of formamidine, its complex with one water molecule, and its complex with two water molecules are 0.9, 2.2, and –5.1 kJ mol –1, respectively. The G3 heat of reaction for the gas-phase decomposition to yield separated products is 22.3 kJ mol–1. Free energies of reaction and of activation in aqueous solution were calculated with PCM using the KLAMT cavity model. At MP2 the formamidine reaction is found to be exergonic in aqueous solution and to favour formation of the separated products (NH3 + HCN). The solvent model predicts a significant lowering of the free energy of activation (16–18 kJ mol–1) for the unimolecular reaction and 21–42 kJ mol–1 for the water-mediated reaction in aqueous solution relative to the gas phase. Key words: decomposition reaction, formamidine, Hartree–Fock, post Hartree–Fock, Gaussian-n theories, IRC, solvation models, PCM, KLAMT.

Thermochemical properties of stable intermediates and derived radicals for the gas-phase formation of 1,3,6,8- and 1,3,7,9-tetrachlorodibenzo- p-dioxins from 2,4,6-trichlorophenol: A computational G3MP2B3 study

For a set of 7 selected stable intermediates and derived radicals for the formation of 1,3,6,8- and 1,3,7,9-tetrachlorodibenzo- p-dioxins from 2,4,6-trichlorophenol, energy minimum structures, total atomic spin densities ρ, harmonic vibrational wavenumbers ν ˜ , principal moments of inertia I A , I B , and I C , heat capacities C p o ( T ) , entropies S o ( T ) , enthalpy increments H o ( T ) − H o ( 0 ) , and standard enthalpies of formation Δ f H o ( T ) were calculated at the G3MP2B3 level of theory and presented for T = 298.15 K . A set of 7 reaction paths is characterized by means of enthalpies of reaction Δ r H o ( 298.15 ) .