Thermochemistry and kinetic analysis on radicals of acetaldehyde + O2, allyl radical + O2 and diethyl and chlorodiethyl sulfides

Thermochemical properties for reactants, intermediates, products and transition states important in the radicals of acetaldehyde + O2 and allyl radical + O2 reaction systems are analyzed with density functional and ab initic calculations, to evaluate the reaction paths and kinetics in oxidation and pyrolysis. Ketene is one important product resulting from acetaldehyde oxidation; thus thermochemistry plus isomerization and conversion reactions of ketene are also analyzed. Enthalpies of formation are determined using isodesmic reaction analysis at the CBSQ composite and density functional levels. Entropies and heat capacities are determined using geometric parameters and vibration frequencies obtained at the HF/6-31G(d\u27) or B3LYP/6-31G(d,p) level of theory. Internal rotor contributions are included in calculation of entropy, S°298, and heat capacities, Cp(T). Rate constants are estimated as a function of pressure and temperature using multifrequency quantum Rice-Ramsperger-Kassel analysis for k(E) and master equation analysis for falloff. A mechanism for pyrolysis and oxidation of acetaldehyde and its\u27 corresponding radicals is constructed. The competition between reactions of radicals of acetaldehyde with O2 versus unimolecular decomposition is evaluated versus temperature and pressure. Thermodynamic parameters, enthalpies, entropies and heat capacities are evaluated for C1 and C2 chlorocarbon molecules and radicals. These thermodynamic properties are used in evaluation and comparison of Cl2 + R. \u3c--\u3e Cl. + RCl reaction rate constants from the kinetics literature for comparison with empirical analysis. Data from some 20 reactions in the literature show linearity on a plot of Eafwd vs Δrxn, fwd, yielding a slope of (0.38 ± 0.04) and an intercept of (10.12 ± 0.81) kcal/mol. The use of Density Functional Theory, B3LYP/6-31g(d,p), with isodesmic working reactions for enthalpy of formation of sulfur hydrocarbons is evaluated using a set of known sulfur hydrocarbon / radical species. Thermodynamic and kinetic parameters for reactants, transition states, and products from unimolecular dissociations of sulfur species related to the chemical agent: CH3CH2SCH2CH2, CH3CH2SCH2CH2Cl, and CH2ClCH2SCH2CH2Cl and corresponding radicals are analyzed. Standard enthalpy, ΔHf°298, for the molecules and radicals are determined using isodesmic reaction analysis at the B3LYP/6-31G(d,p) level, with S°298 and Cp(T) determined using geometric parameters and vibrational frequencies obtained at this same level of theory. Potential barriers for the internal rotor potentials are also calculated at the B3LYP/6-31G(d,p) level, and the hindered rotation contributions to S°298 and Cp(T) are calculated

Section I: Thermodynamic properties of hydrocarbon radicals, peroxy hydrocarbon and peroxy chlorohydrocarbon molecules and radicals Section II: Kinetics and reaction mechanisms for : (1) chloroform pyrolysis and oxidation (2) benzene and toluene oxidation under atmospheric conditions

Alkyl radicals are important active intermediates in gas phase photochemistry and combustion reaction systems. With the exception of a limited number of the most elementary radicals, accurate thermodynamic properties of alkyl radicals are either not available or only rough estimations exist. An H atom Bond Increment approach is developed and a data base [sic] is derived, for accurately estimating thermodynamic properties (ΔHf°298, S°298 and Cp(T)) for generic classes of hydrocarbon radical species. Reactions of alkyl radicals with molecular oxygen are one of the major reaction paths for these radicals in atmospheric photochemistry, oxidation of hydrocarbon liquids and combustion process. Alkyl hydroperoxides are subsequently formed through the alkyl peroxy radicals reactions with varied chemical species present in the reaction system. Thermodynamic properties of the alkyl hydroperoxides and related radicals are therefore frequently required in gas phase modeling and kinetic studies on these systems. The thermodynamic properties of alkyl hydroperoxides, alkyl peroxy radicals and hydroperoxyl-1-ethyl radicals including the species with fluorine and chlorine substituents on the (α-carbon are evaluated using molecular orbital calculations Chloroform is used as a model chlorocarbon system with high Cl/H ratio to investigate thermal decomposition processes of chlorocarbons in oxidative and pyrolytic reaction environments. A detailed reaction mechanism is developed to describe the important features of products and reagent loss and is shown to predict the experimental data well. Reaction pathways and rate constants are developed for CCl3, CCl2 and C2CI3 radical addition to O2 and combination with O, OH HO2 and ClO. The reversible addition reaction of OH radical with benzene to form the hydroxyl-2,4-cyclohexadienyl (benzene-OH) adduct and the subsequent reactions of this benzene OH adduct with O2 are important initial steps for the photooxidation [sic] of benzene and other aromatic species in the atmosphere. OH addition to the benzene ring, the subsequent reaction of O2 with the hydroxyl-2,4-cyclohexadienyl to form hydroxyl-2-peroxy-4-cyclohexenyl (benzene-OH-O2 adduct), are chemical activation reactions and are a function of both pressure and temperature. The kinetics of these two reaction systems at various pressure & temperatures using a quantum version of Rice-Ramsperger-Kassel theory (QRRK) and a modified strong collision approach are analyzed and calculated. The analogue reaction system of toluene photooxidation [sic] is also analyzed. Reaction mechanisms are developed for Initial steps of atmospheric oxidation of benzene and toluene, which include reverse reaction rates determined from thermodynamic parameters and microscopic reversibility. The model results show good agreement with the limited available experimental data

Thermochemistry and kinetics in pyrolysis and oxidation reaction of oxygenate chlorocarbons, neopentane, and ortho-xylene

Thermochemical properties of chlorinated alcohols, chlorinated hydroperoxides and corresponding alkoxy, hydroxy alkyl radicals, peroxy and hydroperoxy alkyl radicals are determined by ab initlo and density functional calculations for modeling and optimization of complex chemical processes for combustion or incineration of chlorinated hydrocarbons. The entropy and heat capacities from vibrational, translational, and external rotational contributions are calculated by statistical mechanics, and the hindered rotational contributions to S°298 and Cp(T)\u27s are calculated by using direct integration over energy levels of the internal rotational potentials. The values of ΔHf°298 are determined using isodesmic reactions with group balance. Groups for use in Benson type additivity estimations are determined for the carbon bonded to oxygen and chlorine(s). Hydrogen bond increment groups for the chloroalkoxy, hydroxy chloroalkyl radicals and interaction terms for peroxy group with chlorine(s) are developed for group additivity approach. The reactions of alkyl radical with oxygen are important rate controlling processes in the low and intermediate temperature chemistry of hydrocarbon oxidation, especially the chemistry which occurs prior to ignition in internal combustion engines and in cool flames. Thermochemical properties for reactants, intermediates, products and transition states in neopentyl radical + O2 reaction system are analyzed with ab initio and density functional calculations to evaluate reaction paths and oxidation kinetics. Rate constants to products and stabilized adducts of the chemically activated neopentyl-peroxy are calculated as function of pressure and temperature using Quantum Rice-RamspergerKassel analysis for k(E) and a master equation analysis for pressure fall-off An elementary reaction mechanism is constructed to model experimental OH and HO2 formation profiles. Aromatic compounds are an important component of higher-octane automotive fuels and consequently they are present in emissions from incomplete combustion and other evaporation from solvents and fuels handling and storage. Oxidation reactions of ortho-xylene are studied to identify the important reaction channels of this class of highoctane aromatics. Elementary reactions, energy well depths, and absolute rate constants of benzylic radical derived from ortho-xylene, 2-methylbenzyl radical with O2, are determined with computational chemistry at density functional levels

Intramolecular Hydrogen Bonding 2021

This book describes the results of both theoretical and experimental research on many topical issues in intramolecular hydrogen bonding. Its great advantage is that the presented research results have been obtained using many different techniques. Therefore, it is an excellent review of these methods, while showing their applicability to the current scientific issues regarding intramolecular hydrogen bonds. The experimental techniques used include X-ray diffraction, infrared and Raman spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), nuclear quadrupole resonance spectroscopy (NQR), incoherent inelastic neutron scattering (IINS), and differential scanning calorimetry (DSC). The solvatochromic and luminescent studies are also described. On the other hand, theoretical research is based on ab initio calculations and the Car–Parrinello Molecular Dynamics (CPMD). In the latter case, a description of nuclear quantum effects (NQE) is also possible. This book also demonstrates the use of theoretical methods such as Quantum Theory of Atoms in Molecules (QTAIM), Interacting Quantum Atoms (IQA), Natural Bond Orbital (NBO), Non-Covalent Interactions (NCI) index, Molecular Tailoring Approach (MTA), and many others

Thermochemistry reaction paths and oxidation kinetics on ketonyl and aldehydic nitrogen oxides, propene and isooctane: a theoretical study

Thermochemical properties for several atmospheric and combustion related species are determined using computational chemical methods coupled with fundamentals of thermodynamics and statistical mechanics. Enthalpies of formation (ΔHf°298) are determined using isodesmic reaction analysis at the CBS-QB3 composite and the B3LYP density functional methods. Entropies (S°298) and heat capacities (Cp°(T)) are determined using geometric parameters and vibration frequencies; internal rotor contributions are included in S and Cp(T) values in place of torsion frequencies. Kinetic parameters are calculated versus pressure and temperature for the chemical activated formation and unimolecular dissociation. Multi-frequency quantum RRK (QRRK) analysis is used for k(E) with Master Equation analysis for fall off. Recommended values for enthalpies of formation of the most stable conformers of nitroacetone, acetonitrite, nitroacetate and acetyl nitrite are -51.6 kcal mol-1, -51.3 kcal mol-1, -45.4 kcal mol-1 and -58.2 kcal mol-1, respectively. The calculated ΔfH º298 for nitroethylene is 7.6 kcal mol-1 and for vinyl nitrite is 7.2 kcal mol-1. The chemically activated R• + NO2 systems associations proceed to RCO• + NO via chemical activation reaction with a fraction to stabilized adducts and lower energy products at atmospheric pressure and temperature. Thermochemical properties of isooctane (2,2,4-trimethyl pentane) and its four carbon radicals from loss of hydrogen atoms, and kinetics of the tertiary isooctane radical reaction with O2 are determined. The computed standard enthalpy of formation of isooctane from this study is -54.40 kcal mol-1. The major products from reaction of the tert-isooctane radical + O2 to form a chemically activated tert-isooctane-peroxy radical are formation of isooctene plus HO2. Next important products are cyclic ethers plus OH radical. This research is the first fundamentally based study of relevant pathways on the potential energy surfaces of tert-isooctane radicals + O2 using high level composite calculation methods. Kinetic modeling for OH addition to propene and subsequent O2 association to the hydroxyl-propyl radical adduct shows that significant forward reaction goes to regenerate OH radicals over the range of temperature and pressure studied. Recycle of OH from the decomposition of the hydroxyl propyl-peroxy radical is up to 78%. Inclusion of activation energy resulting from OH addition to primary carbon (double activation) does not show increase in OH recycle. The introduction of the rate constants presented in this study into existing reaction mechanisms should lead to better kinetic models for olefin oxidation chemistry the atmospheric

Experiment, thermodynamic properties and modeling on combustion of methyl tert-butyl ether : isobutane and isobutene and thermodynamic properties of chloro alkanes and alkenes

The reaction systems: methyl tert-butyl ether (MTBE) unimolecular decomposition, MTBE radicals + O2, tert-butyl radical +O2, isobutene + HOO. (HO2),isobutene + OH, sobutene-OH adducts + O2, and allylic isobutenyl radical + O2, are important systems in the understanding the oxidation chemistry of MTBE, tertiary butyl radical (C3C.), and sobutene, are analyzed. Thermochemical parameters are determined by ah initio Møller-Plesset (MP2(full)/6-31g(d)), complete basis set model chemistry (CBS-4 and CBS-q with MP2(full)/6-31g(d) and B3LYP/6-31g(d) optimized geometries), density functional (B3LYP/631g(d)), semi-empirical MOPAC (PM3) molecular orbital calculations, and by group additivity estimation. Thermochemical kinetic parameters are developed for each elementary reaction path in these complex systems, and a chemical activation kinetic analysis using quantum Rice-Ramsperger-Kassel (QRRK) theory for rate constant function of energy (k(E)) and master equation analysis for falloff is used to calculate rate constants as function of pressure and temperature. Rate constants for HO2 radical addition to carbon-carbon double bond calculated at CBS q//MP2(full)/6-3 IG(d) and CBS-q//B3LYP/6-3 IG(d) levels of theory show similar trends to experimental data: HO2 radical addition to tertiary carbon-carbon double bond (HO2 addition at CD/C2 carbon atom of isobutene) has a lower activation energy than addition to secondary carbon-carbon double bond (CD/C/H), which is lower than addition to primary carboncarbon bond (CD/H2). The Ea for addition to primary carbon-carbon double bonds of ethylene, propene and isobutene also show a decreasing trend. The oxidation and pyrolysis of methyl tert-butyl ether in argon diluent has been studied in a flow reactor over the temperature range 873 to 973 K at atmospheric pressure with residence times between 0.5 - 2 sec. Three mixture compositions of MTBE and oxygen are studied in this MTBE oxidation as well as pyrolysis. Isobutene and methanol are observed as major products from both oxidation and pyrolysis of MTBE experiments. A detailed kinetic model is developed for the pyrolysis and oxidation of MTBE. The mechanism includes oxidation and thermal decomposition of MTBE with major products and important intermediate. The computer code CHENIKIMI is used for numerical integration. Thermodynamic properties for representative multi-chloro alkanes and alkenes determined using the modified group additivity scheme are compared with literature data and show good agreement. The use of limited number of interaction groups provides improved accuracy in calculation of thermodynamic properties for multi-chloro alkanes and alkenes when chlorines are on adjacent carbon atoms. Three multi-chloro Benson type groups plus five interaction groups for chloroalkanes; and two groups plus five interaction groups for chloroalkenes are developed

Theoretical study of the reactivity and energetics of organic radicals

Tese de doutoramento, Química (Química Física), 2010, Universidade de Lisboa, Faculdade de CiênciasOs radicais orgânicos são espécies importantes em quase todos os domínios daquímica e bioquímica. Contudo, apesar da sua existência ter sido documentadahá mais de uma centena de anos, uma fracção significativa da energéticadestas espécies é ainda desconhecida. Uma propriedade termoquímica crucialno estudo de um radical é a entalpia associada à quebra da ligação (BDE)que dá origem a esse radical. Estas BDEs podem ser obtidas experimentalmenteatravés de calorimetria fotoacústica (PAC). A química computacionaltambém pode ser utilizada para fazer previsões rigorosas desta propriedade termoquímica.Os métodos teóricos permitem ainda o acesso directo à estruturade radicais e compostos pais. Neste trabalho, PAC e química computacionalforam utilizadas conjuntamente para estudar a energética de radicais orgânicos.A entalpia de formação padrão do radical ciclopentadienilo e a BDE C H parao 1,3-ciclopentadieno foram reexaminadas. Foi avaliada a precisão de extrapolaçõespara base completa de CCSD(T) e a de métodos de optimização com basena teoria do funcional da densidade. De seguida foi efectuado um estudo detalhadoda energética do grupo alilo. Finalmente, foi estudado o efeito da tensãode anel em hidrocarbonetos cíclicos com cinco e seis membros e respectivosradicais.Organic radicals are important species in virtually every domain of chemistryand biochemistry. However, even though they have been known for morethan 100 years, the energetic data for radicals typically have large uncertaintiesor are missing. One crucial thermochemical property in the study of a radicalis the enthalpy associated with the bond cleavage (BDE) which originates thatradical. BDEs can be obtained experimentally with photoacoustic calorimetry(PAC). Computational chemistry also provides reliable estimates of thisthermochemical property. In addition, theoretical methods provide direct accessto the structure of radicals and their parent compounds. In this work bothPAC and computational chemistry were used to study the energetics of organicradicals. The standard enthalpy of formation for the cyclopentadienyl radicaland the 1,3-cyclopentadienyl C H BDE were re-examined. We proceeded toassess the accuracy of cost-efficient CCSD(T) complete basis set extrapolationschemes and density functional theory optimization methods for radicals. Adetailed analysis of the energetics of the allyl moiety was then conducted. Finally,the effect of ring strain on five- and six-membered ring hydrocarbons andrespective radicals was discussed

Calculating Heat of Formation Values of Energetic Compounds: A Comparative Study

Heat of formation is one of several important parameters used to assess the performance of energetic compounds. We evaluated the ability of six different methods to accurately calculate gas-phase heat of formation (Δ 298,g) values for a test set of 45 nitrogencontaining energetic compounds. Density functional theory coupled with the use of isodesmic or other balanced equations yielded calculated results in which 82% (37 of 45) of the Δ 298,g values were within ±2.0 kcal/mol of the most recently recommended experimental/reference values available. This was compared to a procedure using density functional theory (DFT) coupled with an atom and group contribution method in which 51% (23 of 45) of the Δ 298,g values were within ±2.0 kcal/mol of these values. The T1 procedure and Benson’s group additivity method yielded results in which 51% (23 of 45) and 64% (23 of 36) of the Δ 298,g values, respectively, were within ±2.0 kcal/mol of these values. We also compared two relatively new semiempirical approaches (PM7 and RM1) with regard to their ability to accurately calculate Δ 298,g. Although semiempirical methods continue to improve, they were found to be less accurate than the other approaches for the test set used in this investigation

Computational studies of the structures, reactions, and energetics of selected cyclic and sterically crowded species.

Cheng Mei-Fun.Thesis (M.Phil.)--Chinese University of Hong Kong, 2003.Includes bibliographical references.Abstracts in English and Chinese.Abstract --- p.iAcknowledgements --- p.iiiTable of Contents --- p.ivList of Tables --- p.viList of Figures --- p.viiiChapter Chapter 1 --- Introduction --- p.1Chapter 1.1 --- The Gaussian-3 Method --- p.1Chapter 1.2 --- The G3 Method with Reduced Mφller-Plesset Order and Basis Set --- p.2Chapter 1.3 --- Density Functional Theory (DFT) --- p.3Chapter 1.4 --- Calculation of Thermodynamical Data --- p.3Chapter 1.5 --- Remark on the Location of Transition Structures --- p.3Chapter 1.6 --- Natural Bond Orbital (NBO) Analysis --- p.4Chapter 1.7 --- Scope of the Thesis --- p.4Chapter 1.8 --- References --- p.5Chapter Chapter 2 --- Heats of Formation for the Azine Series: A Gaussian-3 Study --- p.7Chapter 2.1 --- Introduction --- p.7Chapter 2.2 --- Methods of Calculation and Results --- p.8Chapter 2.3 --- Discussion --- p.8Chapter 2.4 --- Conclusion --- p.9Chapter 2.5 --- Publication Note --- p.10Chapter 2.6 --- References --- p.10Chapter Chapter 3 --- Heats of Formation for Some Boron Hydrides: A Gaussian-3 Study --- p.16Chapter 3.1 --- Introduction --- p.16Chapter 3.2 --- Methods of Calculation and Results --- p.18Chapter 3.3 --- Discussion --- p.19Chapter 3.4 --- Conclusion --- p.21Chapter 3.5 --- Publication Note --- p.21Chapter 3.6 --- References --- p.21Chapter Chapter 4 --- Structural and Energetics Studies of Tri- and Tetra-tert-butylmethane --- p.30Chapter 4.1 --- Introduction --- p.30Chapter 4.2 --- Methods of Calculation and Results --- p.32Chapter 4.3 --- Discussion --- p.34Chapter 4.3.1 --- Mono-tert-butylmethane --- p.34Chapter 4.3.2 --- Di-tert-butylmethane --- p.35Chapter 4.3.3 --- Tri-tert-butylmethane --- p.37Chapter 4.3.4 --- Tetra-tert-butylmethane --- p.38Chapter 4.4 --- Conclusion --- p.39Chapter 4.5 --- Publication Note --- p.40Chapter 4.6 --- References --- p.40Chapter Chapter 5 --- A Computational Study of the Diels-Alder Reactions Involving Acenes: Reactivity and Aromaticity --- p.49Chapter 5.1 --- Introduction --- p.49Chapter 5.2 --- Methods of Calculation and Results --- p.50Chapter 5.3 --- Discussion --- p.51Chapter 5.4 --- Conclusion --- p.53Chapter 5.5 --- Publication Note --- p.53Chapter 5.6 --- References --- p.53Chapter Chapter 6 --- A Computational Study of the Charge- Delocalized and Charge-Localized Forms of the Croconate and Rhodizonate Dianions --- p.65Chapter 6.1 --- Introduction --- p.65Chapter 6.2 --- Methods of Calculation and Results --- p.67Chapter 6.3 --- Discussion --- p.68Chapter 6.3.1 --- Charge-Localized Forms of C5052- (C2v) and C6O6 2-(C2v) --- p.68Chapter 6.3.2 --- Charge-Delocalized Forms of C5052- (D5h) and C6062- (D6h) --- p.71Chapter 6.4 --- Conclusion --- p.72Chapter 6.5 --- Publication Note --- p.73Chapter 6.6 --- References --- p.74Chapter Chapter 7 --- Conclusion --- p.89Appendix A --- p.90Appendix B --- p.9