Gas-phase Elimination Reactions Research Articles

Gas-Phase Elimination Reaction of Ethyl (5-cyanomethyl-1,3,4-thiadiazol-2-yl)carbamate: A Computational Study

The gas-phase elimination reaction of ethyl (5-cyanomethyl-1,3,4-thiadiazol-2-yl)carbamate has been studied computationally at the MP2/6–31++G(2d,p) level of theory. The values of the activation parameters and rate constants for the thermal decomposition were evaluated over a temperature range from 405.0 to 458.0 K. The temperature dependence of the rate constants was used to deduce the modified Arrhenius expression: log k405–458 K = (9.01 ± 0.49) + (1.32 ± 0.16) log T – (6946 ± 30) 1/T, which is in good agreement with the expression obtained from experimental data. The results confirm that the mechanism is a cis-concerted elimination that occurs in two steps: The first one corresponds to the formation of ethylene and an intermediate, 5-(cyanomethyl)-1,3,4-thiadiazol-2-yl-carbamic acid, via a six-membered cyclic transition state, and the second one is the decarboxylation of this intermediate via a four-membered cyclic transition step, leading to carbon dioxide and the corresponding 1,3,4-thiadiazole derivative (5-amino-1,3,4-thiadiazole-2-acetonitrile). The connectivity of transition states with their respective minima was verified through intrinsic reaction coordinate calculations, and the progress of the reaction was followed by means of Wiberg bond indices, resulting that both transition states have an “early” character, nearer to the reactants than to the products.

The reaction mechanism of the gas-phase thermal decomposition kinetics of neopentyl halides: A DFT study

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

Quantum chemical calculations of the homogeneous, unimolecular, gas-phase elimination kinetics of primary alkyl acetates and (dimethylamino)alkyl acetates: Neighboring group participation in 4-(dimethylamino)-1-butyl acetate

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.

High-Valent Technetium Fluorides. Does TcF7 Exist?

The structures and stabilities of technetium fluorides in high oxidation states have been studied quantum-chemically at density functional theory (B3LYP) and coupled-cluster (CCSD(T)) levels. The calculations indicate clearly that technetium heptafluoride, TcF7, has a good chance of existence and preparation, thus providing the first heptafluoride in the 4d series. The [TcF6]+ cation, a potential precursor, is also computed to be thermochemically stable against gas-phase elimination reactions. The problem with such highly fluorinated complexes appears thus to be mainly in difficult synthetic access under typical condensed-phase conditions. Matrix-isolation techniques or gas-phase experiments appear to be better suited as starting points.

Where Is the Limit of Highly Fluorinated High‐Oxidation‐State Osmium Species?

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Where Is the Limit of Highly Fluorinated High-Oxidation-State Osmium Species?

The structures and stabilities of various osmium fluorides and oxyfluorides in high oxidation states have been studied by quantum-chemical calculations at DFT (B3LYP), MP2, CCSD, and CCSD(T) levels. The calculations indicate that the homoleptic fluorides all the way up to OsF8 may exist, even though OsF8 will be difficult to prepare. The last missing osmium oxyfluoride, OsOF6, is computed to be thermochemically stable against mononuclear gas-phase elimination reactions. The problem with the nonexistence of such highly fluorinated complexes appears thus to be mainly in difficult synthetic access under typical condensed-phase conditions. Matrix-isolation techniques might provide a means to characterize the highly fluorinated OsVIII and OsVII species.

A density functional theory study of the gas-phase elimination reactions of 4-arylideneimino-1,2,4-triazol-3(2H?)-ones and their 3(2H?)-thione analogues

Theoretical studies on the thermolysis in the gas phase of 4-arylideneimino-1,2,4-triazol-3(2H)-ones and 4-arylideneimino-1,2,4-triazol-3(2H)-thiones were carried out using density functional theory methods, at the B3LYP/6-31G(d) and B3LYP/6-311+G(2d,p) levels of theory. The proposed reaction mechanism occurs in one step, leading to the formation of 3-hydroxy-(2H)-1,2,4-triazole or 3-mercapto-(2H)-1,2,4-triazole and a 4-substituted benzonitrile, via a six-membered cyclic transition state. The progress of the reactions was followed by means of the Wiberg bond indices. The results indicate that the transition states have character intermediate between reactants and products, and the calculated synchronicities show that the reactions are slightly asynchronous, in the case of triazolones, and show a higher asynchronicity in the case of triazolthiones. The bond-breaking processes are slightly more advanced than the bond-forming ones, indicating a small bond deficiency in the transition states. Kinetic and activation parameters for the reactions studied have been calculated and compared with available experimental data.

Gas-phase pyrolysis of thiopheneacetic acids, thienylethanols, and related compounds — protophilicity of ring π-electrons and relative acidities of hydrogen-bond donors of hydroxyl groups

Based on kinetic data of thermal gas-phase elimination reactions, the following Arrhenius log A (s–1) and Ea (kJ mol–1) values, respectively, are obtained: 10.76 and 153.5 for 3-thiopheneacetic acid (1), 10.08 and 149.4 for 2-thiopheneacetic acid (2), 12.04 and 207.1 for 2-(3-thienyl)ethanol (3), 11.55 and 203.3 for 2-(2-thienyl)ethanol (4), 10.91 and 123.4 for 2-thiopheneglyoxylic acid (5), 11.05 and 223.8 for 1-(2-thienyl)propan-1-one (6), and 10.33 and 149.8 for 3-thiophenemalonic acid (7). The products of these pyrolytic reactions were either carbon dioxide or formaldehyde in addition to methylthiophene or thiophenecarboxaldehyde. Both positional and molecular reactivities of the substrates and related compounds are compared, and the results are rationalized on the basis of a reaction pathway involving a concerted six-membered transition state.Key words: thiophenes, gas-phase, pyrolysis, kinetics, mechanism.

Pyrolysis of ?-hydroxyketones and ?-ketoesters: Gas-phase elimination kinetics of 3-hydroxy-3-methyl-2-butanone and methyl benzoylformate

The rates of gas-phase elimination reactions of methyl benzoylformate (1) and 3-hydroxy-3-methyl-2-butanone (2) were obtained at T = 600 K. The two substrates undergo unimolecular first-order elimination for which the Arrhenius equations are, respectively, log k = 13.2 − 53270/(4.574 × 600) for (1) and log k = 12.4 − 53060/(4.574 × 600) for (2). The products of pyrolysis of (1) are benzaldehyde, formaldehyde and CO, while those of (2) are acetaldehyde and acetone. The kinetics of the elimination reactions show benzoylformic acid to be 106-fold more reactive than (1), and pyruvic acid ca. 105-fold more reactive relative to (2); an indication of the rate-controlling part played by the acidity of the hydrogen atom involved in the elimination process of the present compounds in this particular type of reaction. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 295–298, 1997.

Gas-phase pyrolysis in heterocyclic synthesis. Gas-phase elimination reactions of some substituted aminoazoles

Gas-phase pyrolyses of ethyl N-(5-cyanomethyl-1,3,4-thiadiazol-3-yl)carbamate (1), 1-benzoyl-3-(3-methylpyrazol-5-yl)thiourea (2), 1-benzoyl-3-(5-methylisoxazol-3-yl)thiourea (3), and 1-acetyl-3-(3-phenyl-pyrazol-5-yl)thiourea (4) have been studied. These reactions were homogeneous and unimolecular. The kinetics obeyed the first-order rate equation. Utilization of this pyrolytic reaction in heterocyclic synthesis is considered, and mechanistic information has been obtained from kinetic data and product analysis using an on-line pyrolysis GC-MS technique. The physical constants of four new substituted aminoazoles are also described. © 1997 John Wiley & Sons, Inc.

Regioselectivity in gas-phase elimination reactions: 1,2 vs 1,4 and allenic ion vs dienide formation

Gas-phase elimination reactions of deuterium labeled 1-allyl-1-methoxy-6,6-dimethyl-2-cyclohexene ( 1), 1-methoxy-4,4-dimethyl- 1-vinyl-2-cyclohexene ( 2) and 3-methoxy-3-methyl-1-butene ( 3) have been investigated. 1,2-Elimination is the favored pathway when 1 reacts with hydroxide (3.5:1) and methoxide (2.6:1), but 1,4-elimination is preferred with fluoride by 2:1. Abstraction of a vinyl proton in the elimination reactions of 2 and 3 is dominant when amide and/or dimethylamide are used, whereas the loss of an alkyl proton is heavily favored with hydroxide.

The gas-phase elimination reaction of 3-methoxycyclohexene: regiochemistry

Gas-phase elimination reactions of deuterium labeled 3-methoxycyclohexenes have been investigated. 1,4-Elimination is heavily favored over 1,2-elimination when strong bases such as hydroxide and amide are used. The 1,2-pathway becomes more competitive when weaker bases such as methoxide are employed, and the mechanism shifts from E1 cB to E2.

ChemInform Abstract: Mechanism of Base‐Induced Gas‐Phase Elimination Reactions of Cyclic Thioethers

ChemInformVolume 19, Issue 29 Preparative Organic Chemistry ChemInform Abstract: Mechanism of Base-Induced Gas-Phase Elimination Reactions of Cyclic Thioethers L. J. DE KONING, L. J. DE KONING Lab. Org. Chem., Univ. Amsterdam, 1018 WS Amsterdam, Neth.Search for more papers by this authorN. M. M. NIBBERING, N. M. M. NIBBERING Lab. Org. Chem., Univ. Amsterdam, 1018 WS Amsterdam, Neth.Search for more papers by this author L. J. DE KONING, L. J. DE KONING Lab. Org. Chem., Univ. Amsterdam, 1018 WS Amsterdam, Neth.Search for more papers by this authorN. M. M. NIBBERING, N. M. M. NIBBERING Lab. Org. Chem., Univ. Amsterdam, 1018 WS Amsterdam, Neth.Search for more papers by this author First published: July 19, 1988 https://doi.org/10.1002/chin.198829069Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume19, Issue29July 19, 1988 RelatedInformation

Mechanism of base-induced gas-phase elimination reactions of cyclic thio ethers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMechanism of base-induced gas-phase elimination reactions of cyclic thio ethersLeo J. De Koning and Nico M. M. NibberingCite this: J. Am. Chem. Soc. 1988, 110, 7, 2066–2073Publication Date (Print):March 1, 1988Publication History Published online1 May 2002Published inissue 1 March 1988https://doi.org/10.1021/ja00215a009RIGHTS & PERMISSIONSArticle Views117Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (740 KB) Get e-Alerts Get e-Alerts

The mechanism of base-induced gas-phase elimination reactions of thioethers

The mechanism of base-induced gas-phase elimination reactions of thioethers

On the mechanism of base-induced gas-phase elimination reactions of ethers

For the base-induced gas-phase elimination reactions of diethyl ether and cis- and trans-1-tert-butyl-4-methoxy-cyclohexane the kinetic isotope and leaving group effects have been determined as functions of the base strength using the method of Fourier transform ion cyclotron resonance mass spectrometry. The results are interpreted in terms of a variable E2 transition-state structure. Increasing the base strength causes the transition state to shift toward the carbanion or E1cb region of the E2 spectrum, which is also a general phenomenon in the condensed phase. Moreover, it appears that the elimination reactions most readily proceed via a transition state in which the ..beta.. hydrogen and leaving group are periplanar. If the substrate does not easily allow such a relationship, the transition state is found to shift toward the carbenium ion or E1 region of the E2 spectrum where the geometric restrictions of the substrate are less perceptible.

Gas phase elimination reaction of ethylbromoacetate

Ethylbromoacetate was pyrolyzed in a static system and seasoned vessels at temperatures between 339.3 °C–353.3 °C and pressures between 53–166.4 Torr. The rate constant for the homogeneous unimolecular elimination is given by the following Arrhenius equation: log k1(s−1)=(12.62±1.01)−(195.7±9.7) kJ/mol/2.303 RT. In comparing the α-bromo substituent with the α-chloro one in alkyl α-monohaloacetates, the former shows about the same rate as the latter. The lack of a very significant difference in rates may be due to their similar electron withdrawing effect under these reaction conditions.

Gas-phase elimination reactions of ethers induced by amide and hydroxide ions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTGas-phase elimination reactions of ethers induced by amide and hydroxide ionsC. H. DePuy and Veronica M. BierbaumCite this: J. Am. Chem. Soc. 1981, 103, 17, 5034–5038Publication Date (Print):August 1, 1981Publication History Published online1 May 2002Published inissue 1 August 1981https://doi.org/10.1021/ja00407a011RIGHTS & PERMISSIONSArticle Views214Altmetric-Citations61LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (671 KB) Get e-Alerts Get e-Alerts

A facile synthesis of strained bridgehead olefins by a gas-phase elimination reaction

A synthesis of bicyclo[3.3.1]non-1-ene 1 and of a 10:1 mixture of bicyclo[4.2.1]non-1(8)-ene 2 and bicyclo[4.2.1]non-1(2)-ene 3 by gas-phase pyrolysis of the corresponding bridgehead acetates and chlorides is reported.

Strain energy effects in the gas-phase elimination reactions of cycloalkyl chlorides

The gas-phase thermal decompositions of cycloheptyl and cyclo-octyl chloride in a ‘seasoned’ reaction vessel are homogeneous and unimolecular. Rate constants for their elimination of hydrogen chloride are given by the equations k7= 1012·01 ± 0·17 exp –[43,620 ± 240]/RT s–1 and k8= 1011·88 ± 0·22 exp –[42,380 ± 340]/RT s–1. The relationship between these Arrhenius parameters and the difference in strain energy between the cycloalkanes and cycloalkenes is discussed.