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The mechanisms of gas-phase elimination kinetics of 2,2-dimethoxypropane in the presence of hydrogen chloride, trifluoroacetic acid and acetic acid were studied using Moller Plesset, ab initio combined method Complete Basis Set (CBS)-QB3 and various density functional theory methods with 6-311G(d,p) and 6-311++G(d,p) basis sets. The M06-2X/6-311++G(d,p) method provided reasonable agreement with the experimental enthalpy and energy of activation. Formation of 2-methoxypropene and methanol products occurs through six-membered cyclic ring transition state (TS) structure. The TS was characterised by single imaginary frequency, and confirmed through intrinsic reaction coordinate (IRC) calculations. The IRC calculations suggest the development of a van der Waal complex between the 2, 2-dimethoxy propane and the acid catalyst, leading to the TS formation. The process of decomposition in the absence of the acid catalyst requires much higher temperature with an energy of activation above 200 kJ/mol. This f...

The study on the mechanism of the gas-phase elimination or thermal decomposition kinetics of 2, 2-dimethyl-3-butenal has been carried out by using theoretical calculation at MP2, combined ab initio CBSQB3 and DFT (B3LYP, B3PW91, MPW1PW91, PBEPBE, PBE1PBE, CAMB3LYP, M06, B97d) levels of theory. A good reasonable agreement between experimental and calculated parameters was obtained by using CAMB3LYP/6-311G(d,pd) calculations. The contrasted calculated parameters against experimental values suggested decarbonylation reaction to proceed through a concerted five-membered cyclic transition state type of mechanism, involving the hydrogen transfer from the carbonyl carbon to the gamma carbon, consistent with observed kinetic isotope effect. The breaking of alpha carbon–carbonyl carbon bond to produce carbon monoxide is 50% advanced in the transition state. The reaction mechanism may be described as a concerted moderately non-synchronous process. Examination of the Atoms in Molecules (AIM) analysis of electron density supports the suggested mechanism.

The gas-phase kinetics and mechanism of the homogeneous elimination of CO from butyraldehyde in the presence of HCl has been experimentally studied. The reaction is homogeneous and follows the second-order kinetics with the following rate expression: log k1 (s−1 L mol−1) = (13.27 ± 0.36) – (173.2 ± 4.4) kJ mol−1(2.303RT)−1. Experimental data suggested a concerted four-membered cyclic transition state type of mechanism. The first and rate-determining step occurs through a four-membered cyclic transition state to produce propane and formyl chloride. The formyl chloride intermediate rapidly decomposes to CO and HCl gases.

O trabalho apresenta um estudo da produção em História da Educação em Santa Catarina com base no que foi publicado em eventos científicos de caráter regional e nacional, entre os anos de 2000 e 2011. O objetivo é compreender as formas pelas quais se tece o entendimento sobre a escrita da história da educação no estado. Os eventos cotejados foram: os Congressos da SBHE, as Reuniões da ANPED e as reuniões da ANPED Sul. Mapear a produção historiográfica da educação catarinense, circunscrita aos trabalhos publicados nestes eventos, auxiliou na percepção desta historiografia nas injunções das leis de um lugar, de uma prática de pesquisa e de uma escrita constituídas institucional e historicamente e apropriado pelos sujeitos-pesquisadores

Thermal decomposition kinetics of dicyclopentadiene-1,8-dione 7 implied an intramolecular competition between α,β- and β,γ-double bond to assist the CO elimination. Experimental thermolysis of 7 in dioxane gave 3a,7a-dihydro-1H-inden-1-one (cis-bicyclo[4.3.0]nona-2,4,7-triene-9-one), CO gas, and a very small amount of indanone. This result suggested β,γ-double bond favored the extrusion of CO gas. Calculations of several density functional theory (DFT) levels of theory and CBS-QB3 method were employed. Two mechanisms were considered: a one-step concerted pathway and a stepwise mechanism involving [1,3] and [1,5] hydrogen sigmatropic migrations. The CAM-B3LYP/6-31G(d,p) calculation reasonably agrees with the experimental kinetic parameters. The mechanism appears to be unimolecular in one step concerted through a five-membered cyclic transition state. Isomerization of product cis-bicyclo[4.3.0]nona-2,4,7-triene-9-one yielding 1-indanone is presented and described. Calculation from substrate 7 may explain in a similar way the mechanism of decomposition of compounds 1-6. The present work may well promote to the possibility of carrying out experimental research works on the thermal decarbonylation kinetics in a liquid solution and in the gas phase of β,γ-unsaturated aliphatic ketones.

Resumo O caderno escolar é um objeto da cultura material que possibilita à História da Educação compreender o cotidiano da escola. Esse trabalho investigou as práticas de escrita em um caderno de produção de textos pertencente a uma ex-aluna da Escola Normal de Lages, interior do Estado de Santa Catarina, no ano de 1935. Nessa investigação o caderno representou um documento que permitiu entrever parte do processo de negociação entre o prescrito pelo currículo, o trabalho pedagógico e os tipos de escritas desenvolvidas pela normalista. Foram analisadas escritas presentes em redações, cartas e composições livres. O uso do caderno como documento possibilitou compreender as apropriações e os usos deste objeto como portador de sentidos ligados ao sistema de valores e representações sociais que ultrapassam a função de objeto destinado, somente, ao registro do processo de aprendizagem. Abstract The school notebook is an object of material culture that enables history of education to understanding the school's daily life. This work investigated the writing practices in a text production notebook belonging to a former student of the Normal School of Lages, State of Santa Catarina, in the year of 1935. In this research, the school notebook represented a tool that has allowed to see part of the negotiation process between the prescribed by the curriculum, the pedagogical work and the types of writing styles developed by the normalist. Writings were analyzed in texts, such as: essays, letters and free compositions. The use of the notebook as document/source made it possible to understand the appropriations and the uses of this object as bearer of meanings attached to a system of values and social representations that goes beyond the object function aimed only at the record of the learning process. Resumen El cuaderno escolar es un objeto de la cultura material que permite a la Historia de la Educación a entender lo cotidiano de la escuela. Este estudio investigó las prácticas de escritura en un cuaderno de producción de textos pertenecientes a una ex-alumna de la Escuela Normal de Lages, interior del Estado de Santa Catarina, en el año de 1935. En esta investigación, el cuaderno representa una herramienta que permite a vislumbrar parte del proceso de negociación entre prescrito por el currículo, el trabajo pedagógico y los tipos de escritura desarrollado por normalista. Se analizaron las escritas presentes en textos tales como ensayos, cartas y composiciones libres. El uso del cuaderno como un documento/ fuente ha permitido entender la apropiación y los usos de este objeto como portador de significado conectado con el sistema de valores y representaciones sociales que van más allá de la función objeto destinado sólo para el registro del proceso de aprendizaje. Résumé Le cahier d'école est un objet de la culture matérielle qui rend possible à l'Histoire de l'éducation comprendre le quotidien de l'école. Ce travail s'est intéressé pour les pratiques d'écriture dans un cahier de production de textes, appartenant a une ex-étudiante de L'Ecole Normale de Lages, dans l'État de Santa Catarina, dans l'année de 1935. Dans cette recherche, le cahier a représenté un outil qui permet pour identifier une partie du processus de négociation entre ce qui était prescrit dans le curriculum, le travail pédagogique et les écrits développés par l'étudiante. Des écrits présentés sous la forme de récits, lettres et essais ont été analysés. L'usage du cahier comme source d'information a rendu possible comprendre les appropriations et les usages de cet objet, comme porteur de sens liés au système de valeur et les représentations sociales qui vont au delà de la fonction objet destiné uniquement à l'enregistrement du processus d'apprentissage.

The mechanism of the gas-phase elimination allyl cyclohexyl amine, allyl cyclohexyl sulfide, allyl cyclohexyl ether, and allyl ethyl ether has been studied by using ab initio combined methods CBS-QB3, and Density Functional Theory CAM-B3LYP, MPW1PW91, PBE1PBE, M06, and M062X. Products formation is described below: Theoretical calculations of these reactions support the unimolecular process of these gas-phase eliminations. These thermal decompositions undergo a retro-ene type of mechanism and proceed through a non-planar concerted six-membered cyclic transition structure. The energy of activation follow the order allyl ethyl ether (187.0 kJ/mol) > N-allyl cyclohexyl amine (171.7 kJ/mol) > allyl cyclohexyl ether (170.5 kJ/mol) > allyl cyclohexyl sulfide (137.9 kJ/mol). The polarization of C5–Z6 bond, and the electronegativity of the heteroatom (O, N) increases the reaction rate compared to allyl ethyl ether. Conversely, the S atom is positively charged and its electronic effect causes a high dissymmetry in the TS geometry, which appear to accelerate the decomposition. The rate determining step of these substrates is the change in hybridization from sp3 to sp2 reflected in the bond order in C3–C4. Calculated kinetic and thermodynamic parameters from the M06/6-311++G(d,p) level of theory are in reasonable good agreement with the experimental values.

Este artigo apresenta o uso da rede social Facebook, tanto por educandos quanto por educadores, como um recurso tecnológico/pedagógico ao processo de ensino e aprendizagem na modalidade de Educação de Jovens e Adultos - EJA. O escopo desta investigação compreende que os desafios da proposta de uma educação emancipadora passam, também, pelo desenvolvimento e pela discussão sobre a presença e o uso das tecnologias digitais na vida cotidiana, com suas formas peculiares de sociabilidade. Em 2013, a Gerência de Educação do Programa de EJA do SESI, em Santa Catarina, criou no Facebook o Grupo O conhecimento move sua vida. Criado, no primeiro momento, com a função de comunicar e dar visibilidade às atividades desenvolvidas nos diferentes locais de funcionamento da EJA, este espaço virtual tornou-se um significativo e estratégico recurso de disseminação e compartilhamento de práticas e experiências de ensino e aprendizagem. Este artigo traz uma reflexão sobre o uso do Facebook como rede social virtual na educação, sobre a análise das informações publicadas por professores e alunos e, por fim, sobre as diferentes formas de apropriação e ressignificação dessa ferramenta. No âmbito da EJA do SESI, o Facebook contribui com a construção colaborativa do conhecimento e com o desenvolvimento de competências. Curtir, comentar e compartilhar são ações presentes na vida escolar e cotidiana dos sujeitos que vivenciam o processo educativo da EJA do SESI.

Theoretical calculations on the gas-phase thermal decomposition of dimethyldiazirine, diethyldiazirine and difluorodiazirine have been carried out using ab initio composite methods CBS-QB3 and G3, and DFT CAM-B3LYP, MPW1PW91, PBE1PBE and M062X. Reasonable agreement has been found with the experimental values by the G3 method. Two possible mechanisms were studied: Mechanism A consists the opening of the heterocyclic ring with hydrogen transfer to a nitrogen atom to form prop-1-en-2-yldiazene intermediate which later decomposes to nitrogen gas and the corresponding olefin. Mechanism B involves the extrusion of nitrogen molecule with the formation of carbene intermediate which subsequently yields the corresponding olefin. The results obtained from G3 calculations support the mechanism of a carbene intermediate. Population analysis and Wiberg’s bond order show an interaction between the leaving nitrogen and the electron deficient carbon formed during the first step of the reaction.

The mechanisms of the thermal decomposition of cyclohexene (CH), 4-methylcyclohexene (4MCH) and 4-vinyl cyclohexene (4VCH) in the gas-phase were studied by means of electronic structure calculations using perturbation MP2 and Density Functional Theory (DFT) methods. Molecular and diradical reaction pathways were calculated. In the case of the 4-susbstituted cyclohexenes two diradical processes were considered. DFT functionals, including a PT2 correction to the correlation energy, gave reasonable results for all reaction paths considered. Calculated parameters obtained with B2PLYP/6-31+G(d,p) are in good agreement with those reported in Tsang’s experimental study. Evaluated kinetic parameters indicate that CH, 4MCH, and 4VCH should follow the concerted molecular reaction pathway. However, it is possible that a fraction of the reactant molecules could overcome the energy barrier for the radical pathway, because of the high temperatures employed in the experimental conditions. The presence of methyl group in 4MCH slightly favors the breaking of C3 C4 bond. The effect of vinyl group is more dramatic, consisted with a resonance effect stabilizing C3 throughout the bond breaking process. NBO charges suggest these processes are discretely polar, since there are slight variations in the electron density along the reaction coordinates. The analysis of the evolution percentages obtained from bond indexes suggests that these reactions are non-synchronous.

The interactions between zeolites and templates in MFI and MEL (MEL1 and MEL2) structures combined with different conformations of tetrapropylammonium (TPA) and tetrabutylammonium (TBA) templates were investigated using DFT type methods. Molecular dynamics (MD) simulations were carried out with a tight binding code with London dispersion (DFTB-LD) approach to investigate the conformational space of templates before zeolite formation. Conformational preferences are in agreement with experimental results observed in zeolite using TPA and TBA templates when the temperature of synthesis changes. Zeolite–templates interactions were calculated by using both DFT-D and DFTB-LD methods. Analysis of intrinsic zeolite–template interactions and energy changes in zeolites and templates may explain experimental findings. Template distortion energies were evaluated at channel interception distances and anion–cation electrostatic effects were also included to account for template aggregation. A model of cation and anion distribution for MFI zeolite is presented.

The kinetics of the gas-phase thermal decomposition of the α-ketoester methyl benzoylformate was carried out in a static system with reaction vessel deactivated with allyl bromide, and in the presence of the free radical inhibitor propene. The rate coefficients were determined over the temperature range of 440–481 °C and pressures from 32 to 80 Torr. The reaction was found to be homogenous, unimolecular and obey a first-order rate law. The products are methyl benzoate and CO. The temperature dependence of the rate coefficient gives the following Arrhenius parameters: log10 k (s−1) = 13.56 ± 0.31 and Ea (kJ mol−1) = 232.6 ± 4.4. Theoretical calculations of the kinetic and thermodynamic parameters are in good agreement with the experimental values using PBE1PBE/6-311++g(d,p). A theoretical Arrhenius plot was constructed at this level of theory, and the good agreement with the experimental Arrhenius plot suggests that this model of transition state may describe reasonably the elimination process. These results suggest a concerted non-synchronous semi-polar three-membered cyclic transition state type of mechanism. The most advanced coordinate is the bond breaking Cδ+---δ-OCH3 with an evolution of 66.7%, implying this as the limiting factor of the elimination process. Copyright © 2014 John Wiley & Sons, Ltd.

Theoretical calculations of the gas-phase thermal decomposition kinetics of 2-thiomethyl-1-chloroethane and 4-thiomethyl-1-chlorobutane have been carried out by using Density Functional Theory (DFT), composite CBS-Q3, and Moller-Plesset second-order (MP2) methods in order to elucidate a reasonable reaction mechanism of these compounds. The enhanced reactivities of these two substrates, when compared with their parent compounds, attributed to neighboring group participation (NGP) or anquimeric assistance in the literature, were investigated. For 2-thiomethyl-1-chloroethane two dehydrochlorinaton pathways, with and without NGP were studied. The results of quantum chemical estimations of 2-thiomethyl-1-chloroethane in the gas phase show good agreement with experimental values at B3LYP/6-31++G(2d,p) level, and suggest the 1,2-elimination through non-synchronous four-membered cyclic transition state is the preferred mechanism. For 4-thiomethyl-1-chlorobutane, the significant increase in rate compared to 2-thiomethyl-1-chloroethane, together with the formation of a cyclic product tetrahydrothiophene suggest the anchimeric assistance by the CH3S group in the transition state. Best calculated parameters were obtained with CAM-B3LYP/6-31G++(2d,p). Results support the NGP of the thiomethyl group, through cyclic ion-pair type of intermediate. The bond polarization of the C–Cl, in the direction of Cδ+⋯Clδ−, appears to be the rate determining step of these decompositions.

The gas-phase elimination kinetic of 4-bromobutyric acid to give butyrolactone, and hydrogen bromide was studied using Density Functional Theory DFT and Moller-Plesset Perturbation Theory of Second Order MP2 to investigate the more reasonable reaction mechanism. Good agreement of calculated activation parameters with the experimental values was obtained when using PBEPBE/6-31++Gd,p level of theory. Analysis of the calculated thermodynamic and kinetic parameters suggested the reaction mechanism is unimolecular, with involvement of the hydroxyl oxygen of the carboxylic moiety of the substrate assisting the exit of bromide in nucleophilic substitution. The alternate mechanism with the participation of the carbonyl oxygen in a slow step to give an intimate ion-pair intermediate was disregarded due to the high energy of activation. Bond order analysis shows the process is dominated by the breaking of the C-Br bond. The reaction can be described as unimolecular and moderately non-synchronous process.

The mechanisms of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene and their interconversion have been examined at MP2 and DFT levels of theory. These halide substrates yield isoprene and hydrogen chloride. The results MPW1PW91 calculations agree with the experimental kinetic parameters showing the elimination reaction occurs at greater rate for 1-chloro-3-methylbut-2-ene than that for the 3-chloro-3-methylbut-1-ene isomer. The mechanism for the molecular elimination of 1-chloro-3-methylbut-2-ene suggests proceeding through an uncommon six-membered cyclic transition state for alkyl halides in the gas phase, while 3-chloro-3-methylbut-1-ene eliminates through the usual four-membered cyclic transition state. The elongation and subsequent polarization of the C-Cl bond, in the direction of C^{δ+}…Cl^{δ-}, is rate determining step of these reactions. The isomerization of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene was additionally studied. The 1-chloro-3-methylbut-2-ene converts to 3-chloro-3-methylbut-1-ene easier than the reverse reaction. This means that 1-chloro-3-methylbut-2-ene was found thermodynamically more stable than 3-chloro-3-methylbut-1-ene.

The kinetics of the gas-phase thermal decomposition of 2-methyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, and cyclopentanone ethylene ketal were determined in a static system and the reaction vessel deactivated with allyl bromide. The decomposition reactions, in the presence of the free radical suppressor propene, are homogeneous, are unimolecular, and follow first-order law kinetics. The products of these reactions are acetaldehyde and the corresponding ketone. The working temperature range was 459-490 °C, and the pressure range was 46-113 Torr. The rate coefficients are given by the following Arrhenius equations: for 2-methyl-1,3-dioxolane, log k = (13.61 ± 0.12) - (242.1 ± 1.0)(2.303RT)(-1), r = 0.9997; for 2,2-dimethyl-1,3-dioxolane, log k = (14.16 ± 0.14) - (253.7 ± 2.0)(2.303RT)(-1), r = 0.9998; for cyclopentanone ethylene ketal, log k = (14.16 ± 0.14) - (253.7 ± 2.0)(2.303RT)(-1), r = 0.9998. Electronic structure calculations using DFT methods B3LYP and MPW1PW91 with 6-31G(d,p), and 6-31++G(d,p) basis sets suggest that the decomposition of these substrates takes place through a stepwise mechanism. The rate-determining step proceeds through a concerted nonsynchronous four-centered cyclic transition state, and the elongation of the C-OCH(3) bond in the direction C(α)(δ+)...OCH(3)(δ-) is predominant. The intermediate products of these decompositions are unstable, at the working temperatures, decomposing rapidly through a concerted cyclic six-centered cyclic transition state type of mechanism.

The mechanism for the thermal isomerization reactions of 2-methyl-4,5-dihydrofuran was investigated using quantum chemical calculations at B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), and [PBE/6-31G(d,p), PBE/6-31++G(d,p)] levels of theory. It was found that 2-methyl-4,5-dihydrofuran isomerizes to acetylcyclopropane, and by a parallel reaction a slower isomerization to give 3-pentene-2-one. The acetylcyclopropane formation occurs through unimolecular electrocyclic mechanism. The 3-penten-2-one formation also takes place through electrocyclic mechanism, involving [1,2] hydrogen migration. The isomerization reaction of acetylcyclopropane to 3-penten-2-one occurs by step-wise mechanism, with the formation of an intermediate product 2-hydroxy-2,4-pentadiene, which subsequently isomerizes to the keto form, 3-penten-2-one. The step-wise acetylcyclopropane isomerization to 3-penten-2-one has lower energy of activation than the direct conversion of 2-methyl-4,5-dihydrofuran to 3-penten-2-one. Reasonable agreement was found between experimental and calculated energies of activation using B3PW91/6-311G(d,p) and MPW1PW91/6-311G(d,p) methods. Results suggest that both isomerization reactions pathways are possible under the experimental conditions reported. However, the lower energy of activation of the rate determining step of the step-wise mechanism favors this process over the single step mechanism.

The mechanisms for the unimolecular elimination kinetics of selected 1-chloroalkenes in the gas phase were studied at MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), G3, and G3MP2 levels of theory. Two possible unimolecular mechanisms were considered: mechanism A as a concerted 1,2 elimination process through four-membered cyclic transition state (TS). mechanism B describing the anchimeric assistance of the double bond in HCl elimination previously suggested in the literature. Calculated parameters suggest that the elimination reactions of 1-chloroalkenes proceed through mechanism A, in view of the higher energy of activation associated with mechanism B. Density functional method MPW1PW91/6-31G(d,p) calculated parameters gave a better agreement with the experimental values than G3 and G3MP2. The changes along the reaction path of mechanism A were followed by geometric parameters, natural bond orbital charges, and bond order analysis, suggesting the rate-determining process is the breaking of CCl bond in the TS. The dehydrochlorination of chloroalkenes occurs in a concerted nonsynchronous fashion with stabilization of the TS by π-electron delocalization from the neighboring bond. Isomerization reactions for 4-chloro-1-butene, 4-chloro-2-methyl-1-butene, and 4-chloro-1-butene are unlikely at the experimental reaction condition because of the higher the enthalpies and energies of activation. © 2012 Wiley Periodicals, Inc.

The gas-phase thermal elimination of 2,2-diethoxypropane was found to give ethanol, acetone, and ethylene, while 1,1-diethoxycyclohexane yielded 1-ethoxycyclohexene and ethanol. The kinetics determinations were carried out, with the reaction vessels deactivated with allyl bromide, and the presence of the free radical suppressor cyclohexene and toluene. Temperature and pressure ranges were 240.1-358.3 °C and 38-102 Torr. The elimination reactions are homogeneous, unimolecular, and follow a first-order rate law. The rate coefficients are given by the following Arrhenius equations: for 2,2-diethoxypropane, log k(1) (s(-1)) = (13.04 ± 0.07) - (186.6 ± 0.8) kJ mol(-1) (2.303RT)(-1); for the intermediate 2-ethoxypropene, log k(1) (s(-1)) = (13.36 ± 0.33) - (188.8 ± 3.4) kJ mol(-1) (2.303RT)(-1); and for 1,1-diethoxycyclohexane, log k = (14.02 ± 0.11) - (176.6 ± 1.1) kJ mol(-1) (2.303RT)(-1). Theoretical calculations of these reactions using DFT methods B3LYP, MPW1PW91, and PBEPBE, with 6-31G(d,p) and 6-31++G(d,p) basis set, demonstrated that the elimination of 2,2-diethoxypropane and 1,1-diethoxycyclohexane proceeds through a concerted nonsynchronous four-membered cyclic transition state type of mechanism. The rate-determining factor in these reactions is the elongation of the C-O bond. The intermediate product of 2,2-diethoxypropane elimination, that is, 2-ethoxypropene, further decomposes through a concerted cyclic six-membered cyclic transition state mechanism.

The unimolecular gas-phase elimination kinetics of 2-methoxy-1chloroethane, 3-methoxy-1-chloropropane, and 4-methoxyl-1chloroburane has been studied by using density functional theory (DFT) methods to propose the most reasonable mechanisms of decomposition of the aforementioned compounds. Calculation results of 2-methoxy-1-chloroethane and 3-methoxy-1-chloropropane suggest dehydrochlorination through a concerted nonsynchronous four-centered cyclic transition state (TS) to give the corresponding olefin. In the case of 4-methoxyl-1-chloroburane, in addition to the 1,2-elimination mechanism, the anchimeric assistance by the methoxy group, through a polar five-centered cyclic TS, provides additional pathways to give 4-methoxy-butene, tetrahydrofuran and chloromethane. The bond polarization of the CACl, in the direction of C dþ ��� Cl d� , is the limiting step of these elimination reactions. The significant increase in rate together with the formation of a cyclic product tetrahydrofuran in the gas-phase elimination of 4-methoxyl-1-chloroburane is attributed to neighboring group participation of the oxygen of the methoxy group in the TS. The theoretical calculations show a good agreement with the reported experimental results. V C 2011 Wiley

The study of the kinetics and mechanism of dehydrochlorination reaction of 2-methyl benzyl chloride in the gas phase was carried out by means of electronic structure calculations using ab initio Moller-Plesset MP2/6-31G(d,p), and Density Functional Theory (DFT) methods: B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p)], PBE/6-31G(d,p), PBE/6-31++G(d,p). Investigated reaction pathways comprise: Mechanism I, a concerted reaction through a six-centered cyclic transition state (TS) geometry; Mechanism II, a 1,3-chlorine shift followed by beta-elimination and Mechanism III, a single-step elimination with simultaneous HCl and benzocyclobutene formation through a bicyclic type of TS. Calculated parameters ruled out Mechanism III and suggest the elimination reaction may occur by either unimolecular Mechanism I or Mechanism II. However, the TS of the former is 20 kJ/mole more stable than the TS of the latter. Consequently, the Mechanism I seem to be more probable to occur. The rate-determining process is the breaking of C-Cl bond. The involvement of π-electrons of the aromatic system was demonstrated by NBO charges and bond order calculations. The reaction is moderately polar in nature. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 537–546, 2011

The mechanisms for the acid-catalyzed gas-phase dehydration of the tertiary alcohols 2-methyl-2-propanol, 2-methyl-2-butanol, and 2-methyl-2-pentanol were examined at B3LYP/6-31G(d), B3LYP/6-31G(d,p), B3LYP/6-31G(2d,p), B3LYP/6-31G(2d,2p), B3PW1/6-31G(d), B3PW1/6-31G(d,p), B3PW1/6-31G(2d,p), B3PW1/6-31G(2d,2p), MPW91PW91/6-31G(d), MPW91PW91/6-31G(d,p), MPW91PW91/6-31G(2d,p), and MPW91PW91/6-31G(2d,2p) levels of theory. Calculation results suggest that the dehydration processes catalyzed by hydrogen chloride to give the corresponding olefin and water occur with the formation of Van der Waals complexes between the alcohol and hydrogen chloride. The transition states are six-membered cyclic structures involving one molecule of HCl and one of the alcohol. These reactions appear to be molecular in nature. Analysis of the progress along the reaction coordinate, in terms of bond orders, NBO charges, and geometrical parameters suggest these reactions to be moderately polar and nonsynchronous and are dominated by the breaking of the HCl bond, together with an important cleavage of CO bond in the transition state. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

The kinetics and mechanisms of the dehydrochlorination of 2-chloro-1- phenylethane, 3-chloro-1-phenylpropane, 4-chloro-1-phenylbutane, 5-chloro-1-phenylpentane, and their corresponding chloroalkanes were examined by means of electronic structure calculation using density functional theory methods B3LYP/6–31G(d,p), B3LYP/6–31++G(d,p), MPW1PW91/6–31G(d,p), MPW1PW91/6–31++G(d,p), PBEPBE/6–31G(d,p), and PBEPBE/6–31++G(d,p). The potential energy surface was investigated for the minimum energy path. Calculated enthalpies and energies of activation are in good agreement with experimental values using the MPW1PW91 and B3LYP methods. The transition state of these reactions is a four-centered cyclic structure. The reported experimental results proposing neighboring group participation by the phenyl group was not supported by theoretical calculations. The rate-determining process in these reactions is the breaking of ClC bond. The reactions are described as concerted moderately polar and nonsynchronous. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 292–302, 2011

The mechanism of the gas-phase elimination kinetics of 2-ethoxypyridine has been studied through the electronic structure calculations using density functional methods: B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), B3PW91/6-31G(d,p), B3PW91/6-31++G(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), PBEPBE/6-31G(d,p), PBEPBE/6-31++G(d,p), PBE1PBE1/6-31G(d,p), and PBE1PBE1/6-31++G(d,p). The elimination reaction of 2-ethoxypyridine occurs through a six-centered transition state geometry involving the pyridine nitrogen, the substituted carbon of the aromatic ring, the ethoxy oxygen, two carbons of the ethoxy group, and a hydrogen atom, which migrates from the ethoxy group to the nitrogen to give 2-pyridone and ethylene. The reaction mechanism appears to occur with the participation of π-electrons, similar to alkyl vinyl ether elimination reaction, with simultaneous ethylene formation and hydrogen migration to the pyridine nitrogen producing 2-pyridone. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

The kinetics and mechanisms of the gas-phase elimination reactions of neopentyl chloride and neopentyl bromide have been studied by means of electronic structure calculations using density functional methods: B3LYP/6-31G(d,p), B3LYP/ 6-31þþG(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31þþG(d,p), PBEPBE/6-31G(d,p), PBEPBE /6-31þþG(d,p). The reaction channels that account in products formation have a common first step involving a Wagner-Meerwein rearrangement. The migration of the halide from the terminal carbon to the more substituted carbon is followed by beta-elimination of HCl or HBr to give two olefins: the Sayzeff and Hoffmann products. Theoretical calculations demonstrated that these eliminations proceed through concerted asynchronous process. The transition state (TS) located for the rate-determining step shows the halide detached and bridging between the terminal carbon and the quaternary carbon, while the methyl group is also migrating in a concerted fashion. The TS is described as an intimate ion-pair with a large negative charge at the halide atom. The concerted migration of methyl group provides stabilization of the TS by delocalizing the electron density between the terminal carbon and the quaternary carbon. The B3LYP/6-31þþG(d,p) allows to obtain reasonable energies and enthalpies of activation. The nature of these reactions is examined in terms of geometrical parameters, electron distribution, and bond order analysis. V C 2011 Wiley Periodicals, Inc. Int J Quantum Chem 111: 4011-4019, 2011

The kinetic and mechanism of the unimolecular gas-phase elimination of 2-(dimethylamino)ethyl chloride were examined by using density functional theory methods to explain the enhanced reactivity in gas-phase elimination compared to the parent compound ethyl chloride. The plausible anchimeric assistance of the dimethylamino proposed in the literature was investigated. The theoretical calculations were carried out at B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), PBEPBE/6-31G(d,p), and PBEPBE/6-31++G(d,p) levels of theory. The previous proposed reaction path of anchimeric assistance has an energy of activation 60 kJ/mol higher than the experimental value. The located transition state in the minimum energy path is a four-centered cyclic configuration comprising chlorine, hydrogen and two carbon atoms. Calculation results give a lower energy of activation of 2-(dimethylamino)ethyl chloride when compared to the parent compound ethyl chloride. This result is due to the stabilization of the transition state because of electron delocalization involving the dimethylamino substituent.

The products formed in 2-methoxytetrahydropyran elimination reaction in the gas phase are 3, 4-dihydro-2H-pyran and methanol. The kinetic study was carried out in a static system, with the vessels deactivated with allyl bromide, and the presence of the free radical suppressor toluene. Temperature and pressure ranges were 400–450 °C and 25–83 Torr, respectively. The process is homogeneous, unimolecular, and follows a first-order rate law. The observed rate coefficient is represented by the following equation: log k (s−1) = (13.95 ± 0.15) − (223.1 ± 2.1) (kJ mol−1) (2.303RT)−1. The reactant exists mainly in two low energy chair-like conformations, with the 2-methoxy group in axial or equatorial position. However, the transition state (TS) for the elimination of the two conformers is the same. Theoretical calculations of this reaction were carried for two possible mechanisms from these conformations by using DFT functionals B3LYP, MPW1PW91, and PBE with the basis set 6-31G(d,p) and 6-31G++(d,p). The calculation results demonstrate that 2-methoxytetrahydropyran exists mainly in two conformations, with the 2-methoy group in axial or equatorial position, that are thermal in equilibrium. The average thermodynamic and kinetic parameters, taking into account the populations of the conformers in the equilibrium, are in good agreement with experimental values at B3LYP/6-31++(d,p) level of theory. Copyright © 2010 John Wiley & Sons, Ltd.

The gas-phase elimination of kinetics 4-chlorobutan-2-one, 5-chloropentan-2-one, and 4-chloro-1-phenylbutan-1-one has been studied using electronic structure methods: B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), MPW91PW91/6-31G(d,p), MPW91PW91/6-31++G(d,p), PBEPBE/6-31G(d,p), PBEPBE /6-31++G(d,p), and MP2/6-31++G(d,p). The above-mentioned substrates produce hydrogen chloride and the corresponding unsaturated ketone. Calculation results of 4-chlorobutan-2-one suggest a non-synchronous four-membered cyclic transition state (TS) type of mechanism. However, in the case of 5-chloropentan-2-one and 4-chloro-1-phenylbutan-1-one, the carbonyl group assists anchimerically through a polar five-membered cyclic TS mechanism. The polarization of the CCl bond, in the sense of Cδ+…Clδ−, is a rate-determining step in these elimination reactions. The significant increase in rates in the elimination of 5-chloropentan-2-one and 4-chloro-1-phenylbutan-1-one is attributed to neighboring group participation due to the oxygen of the carbonyl group assisting the CCl bond polarization in the TS. Copyright © 2010 John Wiley & Sons, Ltd.

The kinetics and mechanisms of the gas-phase elimination reaction of several alkyl and (dimethylamino)alkyl acetates were studied by means of electronic structure calculations using MP2/6-31G(d,p) and DFT B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), PBEPBE/6-31G(d,p), PBEPBE/6-31++G(d,p) level of theory. Theoretical calculations demonstrated that ethyl acetate, 2-(dimethylamino)ethyl acetate, propyl acetate, 3-(dimethylamino)propyl acetate, and butyl acetate decompositions proceed through a concerted six-membered cyclic transition state to give acetic acid and the corresponding olefin. Conversely, an alternative path occurs for 4-(dimethylamino)butyl acetate, where a late transition state structure resembles the products N-methylpyrrolidine and methyl acetate. The observed products and the nature of the TS suggest that the nitrogen atom assists the elimination of the acetate. An intimate ion-pair intermediate has been considered, followed by decomposition to the final products methyl acetate and N-methyl pyrrolidine. The high reaction rate observed in 4-(dimethylamino)butyl acetate when compared to the parent compound is discussed. The nature of these reactions is examined in terms of geometrical parameters, electron distribution, and bond order analysis.

The gas-phase elimination kinetics of N-benzylglycine ethyl ester was examined in a static system, seasoned with allyl bromide, and in the presence of the free chain radical suppressor toluene. The working temperature and pressure range were 386.4-426.7 degrees C and 16.7-40.0 torr, respectively. The reaction showed to be homogeneous, unimolecular, and obeys a first-order rate law. The elimination products are benzylglycine and ethylene. However, the intermediate benzylglycine is unstable under the reaction conditions decomposing into benzyl methylamine and CO(2) gas. The variation of the rate coefficients with temperature is expressed by the following Arrhenius equation: log k(1) (s(-1)) = (11.83 +/- 0.52) - (190.3 +/- 6.9) kJ mol(-1) (2.303RT)(-1). The theoretical calculation of the kinetic parameters and mechanism of elimination of this ester were performed at B3LYP/6-31G*, B3LYP/6-31+G**, MPW1PW91/6-31G*, and MPW1PW91/6-31+G** levels of theory. The calculation results suggest a molecular mechanism of a concerted nonsynchronous six-membered cyclic transition state process. The analysis of bond order and natural bond orbital charges implies that the bond polarization of C(=O)O-C, in the sense of C(=O)O(delta-)...C(delta+), is rate determining. The experimental and theoretical parameters have been found to be in reasonable agreement.

The gas-phase elimination of 1,1-dimethoxycyclohexane yielded 1-methoxy-1-cyclohexene and methanol. The kinetics were determined in a static system, with the vessels deactivated with allyl bromide, and in the presence of the free radical inhibitor cyclohexene. The working temperature was 310–360 -C and the pressure was 25–85 Torr. The reaction was found to be homogeneous, unimolecular, and follows a first-order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equation: log k(s S1 ) ¼ [(13.82 W 0.07) – (193.9 W 1.0)(kJ mol S1 )](2.303RT) S1 ; r ¼ 0.9995. Theoretical calculations were carried out using density functional theory (DFT) functionals B3LYP, MPW1PW91, and PBE with the basis set 6-31G(d,p) and 6-31GRR(d,p). The calculated values for the energy of activation and enthalpy of activation are in reasonably good agreement with the experimental values using the PBE/6-31G (d,p) level of theory. Both experimental results and theoretical calculations suggest a molecular mechanism involving a concerted polar four-membered cyclic transition state. The transition state structure of methanol elimination from 1,1-dimethoxycyclohexane is characterized by a significantly elongated C—O bond, while the Cb—H bond is stretched to a smaller extent, as compared to the reactant. The process can be described as moderately asynchronic with some charge separation in the TS. Copyright 2010 John Wiley & Sons, Ltd. Supporting information may be found in the online version of this paper.

The kinetics of the thermal decomposition of the title compounds in the gas phase have been studied at the B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), MPW91PW91/6-31G(d,p), MPW91PW91/6-31++G(d,p), PBEPBE/6-31G(d,p), and PBEPBE/6-31++G(d,p) levels of theory. These halide substrates produce the corresponding cyclohexadiene and hydrogen chloride. The DFT calculations suggest a non-synchronous four-membered cyclic transition state type of mechanism. The elongation and subsequent polarization of the C–Cl bond, in the direction of C δ+ …Cl δ− , is rate determining step in these elimination reactions. Differences in reactivity in these substrates are discussed in terms of the transition state structure and electron distribution.

Theoretical calculation of the kinetics and mechanisms of gas-phase elimination of 2-hydroxyphenethyl chloride and 2-methoxyphenethyl chloride has been carried out at the MP2/6-31G(d,p), B3LYP/6-31G(d,p), B3LYP/6-31 + G(d,p), B3PW91/6-31G(d,p) and CCSD(T) levels of the theory. The two substrates undergo parallel elimination reactions. The first process of elimination appears to proceed through a three-membered cyclic transition state by the anchimeric assistance of the aromatic ring to produce the corresponding styrene product and HCl. The second process of elimination occurs through a five-membered cyclic transition state by participation of the oxygen of o-OH or the o-OCH3 to yield in both cases benzohydrofuran. The B3PW91/6-31G(d,p) method was found to be in good agreement with the experimental kinetic and thermodynamic parameters for both substrates in the two reaction channels. However, some differences in the performance of the different methods are observed. NBO analysis of the pyrolysis of both phenethyl chlorides implies a CCl bond polarization, in the sense of Cδ+…Clδ−, which is a rate-determining step for both parallel reactions. Synchronicity parameters imply polar transition states of these elimination reactions. Copyright © 2009 John Wiley & Sons, Ltd.

The gas phase elimination kinetics of racemic methyl mandelate was determined in a static system, and yielded on decomposition benzaldehyde, methanol, and carbon monoxide. The reaction was homogeneous, unimolecular, and follows a first-order law in the temperature range 379.5-440 degrees C and pressure range of 21.5-71.1 Torr. The variation of the rate coefficient with temperature is expressed by the following Arrhenius equation: log k1 = (12.70 +/- 0.14)-(206.5 +/- 1.9) kJ/mol (2.303RT)(-1). The theoretical estimations of the kinetics and thermodynamics parameters were carried out using DFT methods B3LYP, B3PW91, MPW1PW91, and PBEPBE. Calculation results are in reasonably good agreement with the experimental energy and enthalpy values when using the PBEPBE DFT functional. However, regarding the entropy of activation, the MPW1PW91 functional is more adequate to describe the reaction. These calculations imply a molecular concerted nonsynchronous mechanism involving a two-step process, where the formation of the unstable alpha-lactone intermediate is the rate-determining factor. The lactone intermediate rapidly decarbonylates to produce benzaldehyde and carbon monoxide. The transition state is late in the reaction coordinate, resembling the lactone configuration.

Theoretical study of the elimination kinetics of 2-phenylethanol, 1-phenyl-2-propanol, and 2-methyl-1-phenyl-2-propanol in the gas-phase has been carried out at the MP2/6-31G(d,p), B3LYP/6-31G(d,p), B3LYP/6-31++G(d,p), MPW1PW91/6-31G(d,p), MPW1PW91/6-31++G(d,p), PBEPBE/6-31G(d,p), and PBEPBE/6-31++G(d,p) levels of theory. The three substrates undergo two parallel elimination reactions. The first elimination appears to proceed through a six-membered cyclic transition state to give toluene and the corresponding aldehyde or ketone. The second parallel elimination takes place through a four-membered cyclic transition state producing water and the corresponding unsaturated aromatic hydrocarbon. Results from MP2/6-31G(d,p) and MPW1PW91/6-31++G(d,p) methods were found to be in good agreement with the experimental kinetic and thermodynamic parameters in the formation of toluene and the corresponding carbonyl compound. However, the results for PBEPBE/6-31G(d,p) were in better agreement with the experimental data for the second parallel reaction yielding water and the corresponding unsaturated aromatic hydrocarbon. The charge distribution differences in the TS related to the substitution by methyl groups in the substrates can account for the observed reaction rate coefficients. The synchronicity parameters imply semi-polar transition states for these elimination reactions. Copyright © 2009 John Wiley & Sons, Ltd.

The reaction paths for the gas-phase molecular elimination of triethyl and trimethyl orthoesters were examined at B3LYP/6-31G(d,p), B3LYP/6-31G++(d,p), B3PW91/6-31G(d,p), B3PW91++G(d,p), MPW1PW91/6-31G(d,p), and MPW1PW91/6-31++G(d,p) levels of theory. The thermal decomposition of ethyl and methyl orthoesters involves similar transition state configurations in a four-membered ring arrangement. Products formed are ethanol and the corresponding unsaturated ketal for ethyl orthoesters, while in methyl orthoesters are methanol and the corresponding unsaturated ketal. Calculated thermodynamic and kinetic parameters from B3LYP calculations were found to be in good agreement with the experimental values. The calculated data imply the polarization of the C3-O4, in the direction C3(delta+)...O4(delta-), is rate determining. The NBO charges, bond indexes, and synchronicity parameters suggest the elimination reactions of ethyl orthoesters occur through a more polar asynchronic mechanism compared to methyl orthoesters.

The elimination kinetic of methyl carbazate in the gas phase was determined in a static system over the temperature range of 340–390 °C and pressure range of 47–118 Torr. The reaction is homogeneous, unimolecular, and obeys a first order rate law. The decomposition products are methyl amine, nitrous acid, and CO gas. The variation of the rate coefficients with temperatures is given by the Arrhenius expression: log k1 (s−1) = (11.56 ± 0.34) − (180.7 ± 4.1) kJ mol−1(2.303 RT)−1. The estimated kinetics and thermodynamics parameters are in good agreement to the experimental values using B3LYP/6-31G (d,p), and MP2/6-31G (d,p) levels of theory. These calculations imply a molecular mechanism involving a concerted non-synchronous quasi three-membered ring cyclic transition state to give an unstable intermediate, 1,2-oxaziridin-3-one. Bond order analysis and natural charges implies that polarization of O (alkyl)C (alkyl) bond of the ester is rate determining in this reaction. Copyright © 2008 John Wiley & Sons, Ltd.

The mechanisms of the homogeneous, unimolecular, gas-phase elimination kinetics of several methyl ω-chloroesters were examined by using the ‘ab initio’ and DFT level of theories. Theoretical calculations of dehydrochlorination of methyl 3-chloropropionate suggest a planar concerted, non-synchronous, four-membered cyclic transition state to give methyl acrylate. However, the parallel competitive gas-phase elimination of methyl 4-chlorobutyrate and methyl 5-chlrovalerate occurs through neighboring group participation to render methyl chloride and the corresponding lactone through a concerted, semi-polar five- and six-membered cyclic transition state type of mechanism. Calculated thermodynamic and kinetic parameters reasonably agree with the experimental values at DFT B3LYP/6-31G* theory level. Geometrical parameters, NBO charges and bond indexes showed strong polarization at Cδ+···Clδ− bond in the transition state suggesting the breaking of CCl bond as rate-determining factor for both dehydochlorination and lactone formation reactions. The synchronicity parameters suggest a concerted polar mechanism implying a TS which has ion-pair character for lactone product formation. Copyright © 2008 John Wiley & Sons, Ltd.

The mechanisms for the gas phase molecular elimination kinetics of 2,2-diethoxy-ethylamine and 2,2-diethoxy-N,N-diethyl-ethylamine were examined at MP2/6-31G, B3LYP/6-31G, B3LYP/6-31G(d,p), MPW91PW91/6-31G. MPW91PW91/6-31G(d,p), PBEPBE/6-31G, and PBEPBE/6-31G(d,p) levels of theory. These elimination processes involve two parallel reactions. The first parallel reaction gives ethanol and the corresponding 2-ethoxyethenamine. The latter compound further decomposes to ethylene, CO, and the corresponding amine. The second parallel reaction produces ethane and the corresponding ethyl ester of an α-amino acid. Calculated thermodynamic and kinetic parameters from PBEPBE calculations were found to be in good agreement with the experimental values. The transition states of the parallel reactions are best described as four-membered cyclic structures. The intermediate 2-ethoxy-ethenamine undergoes a consecutive elimination through a six-membered cyclic transition state mechanism. Bond indexes and synchronicity (Sy) parameters are in agreement with concerted semi-polar transition state structures. Copyright © 2008 John Wiley & Sons, Ltd.

The theoretical study of the gas-phase pyrolysis kinetics of several tert -nitroalkanes, 2-methyl-2-nitropropane, 2-methyl-2-nitrobutane, and 2, 3-dimethyl-2-nitrobutane, has been carried out at the MP2/6-31G(d), B3LYP/6-31G(d), B3PW91/6-31G(d), levels of theory. The nitroalkanes yield the corresponding alkene and HNO 2 gas in a rate determining step. The B3PW91/6-31G(d) method was found to give a reasonable good agreement with the experimental kinetic and thermodynamic parameters. The elimination of these reactions suggest a concerted non-synchronous five-membered cyclic transition state type of mechanism.

The mechanisms of the gas phase elimination of N,N-dimethylglycine, picolinic acid, and N-phenylglycine and their ethyl esters have been examined at Moller–Plesset MP2/6-31G (d, p) level of theory. The ethyl esters of these 2-amino carboxylic acids produce the corresponding amino carboxylic acid and ethylene in a rate-determining step. However, the unstable intermediate amino carboxylic acid rapidly decarboxylate to give the corresponding amino compound. These calculations imply a concerted, semi-polar six-membered cyclic transition state type of mechanism for the ethyl esters, and a non-synchronous five-membered cyclic transition state for the amino acids decarboxylation. The present results support previous mechanistic consideration of the elimination of the above-mentioned compounds in the gas phase. Copyright © 2008 John Wiley & Sons, Ltd.

The gas-phase elimination kinetics of the title compounds were carried out in a static reaction system and seasoned with allyl bromide. The working temperature and pressure ranges were 200–280 °C and 22–201.5 Torr, respectively. The reactions are homogeneous, unimolecular, and follow a first-order rate law. These substrates produce isobutene and corresponding carbamic acid in the rate-determining step. The unstable carbamic acid intermediate rapidly decarboxylates through a four-membered cyclic transition state (TS) to give the corresponding organic nitrogen compound. The temperature dependence of the rate coefficients is expressed by the following Arrhenius equations: for tert-butyl carbamate logk1 (s−1) = (13.02 ± 0.46) – (161.6 ± 4.7) kJ/mol(2.303 RT)−1, for tert-butyl N-hydroxycarbamate logk1 (s−1) = (12.52 ± 0.11) – (147.8 ± 1.1) kJ/mol(2.303 RT)−1, and for 1-(tert-butoxycarbonyl)-imidazole logk1 (s−1) = (11.63 ± 0.21)–(134.9 ± 2.0) kJ/mol(2.303 RT)−1. Theoretical studies of these elimination were performed at Moller–Plesset MP2/6-31G and DFT B3LYP/6-31G(d), B3LYP/6-31G(d,p) levels of theory. The calculated bond orders, NBO charges, and synchronicity (Sy) indicate that these reactions are concerted, slightly asynchronous, and proceed through a six-membered cyclic TS type. Results for estimated kinetic and thermodynamic parameters are discussed in terms of the proposed reaction mechanism and TS structure. Copyright © 2007 John Wiley & Sons, Ltd.

The gas-phase elimination kinetics of 2-arylethyl N , N -dimethylcarbamates, (CH 3 ) 2 NCOOCH 2 CH 2 Ar, has been studied at the ab initio MP2/6-31G and MPW1PW91/6-31G(d,p) levels of theory. These carbamates produce N , N -dimethylcarbamic acid and the corresponding 4-substituted styrene in a rate determining step. The unstable intermediate N , N -dimethylcarbamic acid rapidly decarboxylate through a four-membered cyclic transition state to give dimethylamine . These calculations imply a concerted, non-synchronous six-membered cyclic transition state type of mechanism. The present results support the fact that the acidity of the benzylic hydrogen as an important factor for faster elimination rates.

The kinetics of the gas-phase elimination kinetics of CO2 from furoic acid was determined in a static system over the temperature range 415–455°C and pressure range 20–50 Torr. The products are furan and carbon dioxide. The reaction, which is carried out in vessels seasoned with allyl bromide and in the presence of the free-radical suppressor toluene and/or propene, is homogeneous, unimolecular, and follows a first-order rate law. The observed rate coefficient is expressed by the following Arrhenius equation: log k1(s−1) = (13.28 ± 0.16) − (220.5 ± 2.1) kJ mol−1 (2.303 RT)−1. Theoretical studies carried out at the B3LYP/6-31++G** computational level suggest two possible mechanisms according to the kinetics and thermodynamic parameters calculated compared with experimental values. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 298–306, 2007

Theoretical studies for the kinetics of the gas phase elimination of 2-hydroxynitroalkanes were carried out at MP2/6-31G* level of theory. The mechanism for both secondary and tertiary 2-hidroxynitroalkanes thermolysis is retro-aldol type. In the case of the secondary 2-hydroxynitroalkanes, that is, 3-nitro-2-butanol and 3-nitro-2-pentanol, the elimination reaction proceeds via a six-membered cyclic transition state with the formation of actetaldehyde and the corresponding nitroalkane. In the case of the tertiary 2-hydroxynitroalkane, 2-methyl-3-nitro-2-propanol, the reaction also proceeds through a six-membered cyclic transition state to give acetone and nitromethane. The calculated kinetic and thermodynamic parameters are in reasonable agreement with the reported experimental values. NBO charges revealed that polarization of both Nδ+C and CC bonds are important factors in the decomposition process. The tertiary substrate is favored due to stabilization of the C positive charge in the TS. The NBO analysis showed that these reactions are concerted and polar in nature. Copyright © 2006 John Wiley & Sons, Ltd.

The homogeneous, unimolecular, gas-phase elimination kinetics of several heterocyclic carbamates was studied at the MP2/6-31G level of theory under the average experimental conditions for each substrate. The elimination products for these carbamates are the corresponding carbamic acid and isobutylene. The intermediate acids are unstable and decarboxylate at the reaction temperature. Calculated thermodynamic and kinetic parameters are in good agreement with the experimental values, displaying the same reactivity order observed experimentally. An increase in the electron-withdrawing effect of the substituent on the carbamate nitrogen, increases the elimination rate. Transition state structures are described as six-membered rings with some departure from planarity. NBO charge analysis reveals strong polarization at the O(ester) δ−Cδ+ bond. Bond indexes and synchronicity parameters are consistent with a concerted polar type of mechanism with O(ester) δ−Cδ+ bond breaking as the most important process. Copyright © 2007 John Wiley & Sons, Ltd.

The gas-phase elimination of ethyl N,N-dimethylcarbamates substituted with electron-withdrawing groups at the 2-position of the ethyl were studied by using the Moller–Plesset MP2/6-31G method. Calculations suggest a concerted non-synchronous six-membered cyclic transition state type of mechanism of the above-mentioned carbamates. These substrates undergo thermal elimination to produce the N,N-dimethylcarbamic acid and the corresponding substituted olefin in the rate-determining step. The unstable intermediate, N,N-dimethylcarbamic acid rapidly decomposes through a four-membered cyclic transition state to dimethylamine and CO2 gas. The logarithm of relative theoretical rate coefficients when plotted against original Taft's σ* values gave an approximate straight line (ρ*=−0.137±0.023, r=0.9610 at 360 °C). In addition to this fact, plotting experimental log krel. against the theoretical log krel. for 2-substituted ethyl N,N-dimethylcarbamates an approximate straight line (r=0.9578 at 360 °C) is obtained, which means similar mechanism.