A Quantum-Chemical Study of the C2H3F2+ and C2H3Cl2+ Isomers and Their Interconversion. CBS-QB3 Proton Affinities of Difluoroethenes and Dichloroethenes

Frash, MV; Hopkinson, and Alan C.; Böhme, Diethard K.

doi:10.1021/jp9915477

Cited by 4 publications

(4 citation statements)

References 49 publications

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“…Hydride abstraction, which is the characteristic ionization process observed with alkanes and alkenes under our experimental conditions,11 is expected to be particularly favorable in the case of 1,1‐DCA due to the high stability of the 1,1‐dichloroethyl cation resulting from hydride removal from C‐1. In a recent quantum‐chemical study, the 1,1‐dichloroethyl cation was indeed found to represent the global minimum on the potential energy surface calculated for the C 2 H 3 Cl 2 + species 12. Similarly stabilized [M − H] + species are expected from 1,1,2‐TCA and 1,1,2,2‐TCA.…”

Section: Resultsmentioning

confidence: 83%

Ion chemistry of chloroethanes in air at atmospheric pressure

Nicoletti

Paradisi

Scorrano

2001

Rapid Comm Mass Spectrometry

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Ion chemistry at atmospheric pressure is of major relevance to novel methods for the abatement of volatile organic compounds (VOCs) that employ non-thermal plasmas. For this reason, positive and negative APCI (atmospheric pressure chemical ionization) mass spectra of all six di-, tri- and tetrachloroethanes diluted in air (500-1500 ppm) at atmospheric pressure were investigated at 30 °C and at 300 °C. Spectral changes due to collisional activation of the ions achieved by increasing δV, the potential difference between sampling and skimmer cones, are informative of structures and ion-molecule reactions. Positive ion chemistry of the chloroethanes (M) can, in general, be ascribed to C-C and C-Cl cleavages of the molecular ion, M+•, never detected but likely formed via exothermic charge exchange from primary ions of the APCI plasma. Exceptions to this characteristic pattern were observed for 1,1-dichloroethane and 1,1,2,2-tetrachloroethane, which give [M - H]+ and [M - HCl]+• species, respectively. It is suggested that both such species are due to ionization via hydride transfer. Upon increasing δV, the [M - HCl]+• ion formed from 1,1,2,2-tetrachloroethane undergoes the same fragmentation and ion-molecule reactions previously reported for trichloroethene. A nucleophilic reaction of water within the [C2H4Cl+](H2O)n ionic complexes to displace HCl is postulated to account for the [C2H5O+](H2O)m species observed in the positive APCI spectra of the dichloroethanes. Negative ion spectra are, for all investigated chloroethanes, dominated by Cl- and its ion-neutral complexes with one, two and, in some cases, three molecules of the neutral precursor and/or water. Another common feature is the formation of species (X-) (M)n where X- is a background ion of the APCI plasma, namely O2 -,O3 - and, in some cases, (NO)2 -. Peculiar to 1,1,1-trichloroethane are species attributed to Cl- complexes with phosgene, (Cl-)(Cl2C=O)n(n = 1,2). Such complexes, which were not observed for either the isomeric 1,1,2-trichloroethane or for the tetrachloroethanes, are of interest as oxidation intermediates in the corona-induced decomposition process. No conclusions can be drawn in the case of the dichloroethanes, since, for these compounds, the ions (Cl-)(Cl2C=O)n and (Cl-)(M)n happen to be isobaric

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Section: Resultsmentioning

confidence: 83%

Ion chemistry of chloroethanes in air at atmospheric pressure

Nicoletti

Paradisi

Scorrano

2001

Rapid Comm Mass Spectrometry

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“…The process appears straightforward in the case of the ion derived from 1,1,1 , which should have the structure of the 1,1‐difluorotrichloroethyl cation ( g ) (Scheme ). The same species could also be formed from 1,1,1,2 via Cl loss from C‐2; in this case, however, the alternative Cl loss from C‐1 should be favored since the ionic product h is expected to be more stable than g in view of recently published data for the difluoro‐ and dichloroethyl cations 5. Finally, halogen transposition is necessarily implied in the CF 2 elimination from C 2 Cl 3 F 2 + ions deriving from 1,1,2 (Scheme ).…”

Section: Resultsmentioning

confidence: 98%

“…In the latter field, various ion‐etching techniques for microcircuit fabrication (ion milling, ion etching, sputter etching) should be mentioned, in addition to promising new technologies for the treatment of volatile organic compounds (VOCs) which make use of non‐thermal plasmas 3. In addition to the specific interest associated with the applied fields, fundamental knowledge is being actively pursued about the effects of substitution by halogens, notably fluorine and chlorine, on the structures, energetics and reactivity of simple carbenium ions and related species 4–6. Such knowledge is based on the results of experimental investigations which are often integrated with those of theoretical studies.…”

Section: Introductionmentioning

confidence: 99%

Isomerization and dissociation of C₂X₅⁺ and C₂X₄^+· ions (X = Cl, F) from chlorofluoroethanes in an ion trap mass spectrometer

Marotta

Paradisi

2002

J. Mass Spectrom.

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The collision-induced dissociation of C(2)X(5)(+) (C(2)Cl(2)F(3)(+), C(2)Cl(3)F(2)(+) and C(2)Cl(4)F(+)) and C(2)X(4)(+.) ions (C(2)ClF(3)(+*), C(2)Cl(2)F(2)(+*), and C(2)ClF(3)(+*)) derived from three chlorofluoroethanes (the isomeric 1,1,1- and 1,1,2-trichlorotrifluoroethane and 1,1,1,2-tetrachlorodifluoroethane) was investigated by means of multi-stage mass spectrometric (MS(n)) experiments in an ion trap mass spectrometer. The observation of a common dissociation pattern for ions of any given elemental composition suggests that the experiments could not differentiate isomeric C(2)X(5)(+) ions formed from different neutral precursors and originally having different structures. For any given elemental composition, a common dissociation pattern was observed, suggesting that energy barriers for isomer interconversion are lower than for dissociation. For ions containing two or more fluorine atoms, the major (in some cases unique) dissociation involves C-C cleavage to form CX(3)(+) and CF(2). Energetically, CF(2) loss is always the most favorable reaction; mechanistically it implies, at least in some cases, rearrangement via halogen transfer from one carbon to the other (for example, in the case of the C(2)Cl(2)F(3)(+) species derived from 1,1,1-trichlorotrifluoroethane, which should have initially the Cl(2)C(+)-CF(3) structure). Similar behavior was observed with C(2)X(4)(+*) ions produced both from the three chlorofluoroethanes and from model alkenes (trifluorochloroethene and tetrachloroethene). The dissociation behavior of these C(2)X(4)(+*) species is characteristic of the ion composition, with no memory of the original neutral precursor structure. Specifically, C(2)Cl(2)F(2)(+*) ions dissociate uniquely via loss of CF(2), C(2)ClF(3)(+*) ions eliminate preferentially CF, with CF(2) loss being only a minor reaction, whereas C(2)Cl(3)F(+*) and C(2)Cl(4)(+*) dissociate exclusively via Cl elimination.

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“…15,16 Outras propriedades muito estudadas são as afinidades por próton [17][18][19][20][21][22][23] e por elétron, [24][25][26][27] a acidez, 28 bem como a identificação da estrutura mais estável para um determinado isômero. 29,30 Compostos inorgânicos também podem ser explorados utilizando métodos compostos pelo cálculo do potencial de redução 31 em reações de óxido-redução.…”

Section: Introductionunclassified

Comparação entre métodos compostos no cálculo de afinidades por próton e elétron em sistemas moleculares

Lima

Morgon

2010

Quím. Nova

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. The CBS-4M, CBS-QB3, G2, G2(MP2), G3 and G3(MP2) model chemistry methods have been used to calculate proton and electron affinities for a set of molecular and atomic systems. Agreement with the experimental value for these electronic properties is quite good considering the uncertainty in the experimental data. A comparison among the six theories using statistical analysis (average value, standard deviation and root-mean-square) showed a better performance of CBS-QB3 to obtain these properties.Keywords: composite methods; CBS-QB3 method; proton and electron affinities. INTRODUÇÃOA partir da década de 1980 começaram a surgir métodos para obter a energia eletrônica de sistemas moleculares, utilizando cálculos teóricos em diferentes níveis de teoria e com conjuntos de funções de base específicos para cada um desses níveis. Estes métodos ficaram conhecidos como métodos compostos. A principal idéia por trás destes métodos é obter a energia eletrônica na geometria de equilíbrio de forma aditiva, ou seja, calculada pela soma das contribuições de cada etapa do cálculo.Existem diversos métodos computacionais, sendo os mais utilizados aqueles que derivam da teoria Gaussian desenvolvidos por Pople e colaboradores 1-4 e da teoria do Conjunto de Base Completo desenvolvidos por Petersson e colaboradores. 5,6Usando a energia do sistema é possível obter propriedades termodinâmicas como a entalpia e a energia livre de Gibbs. Assim, através da variação da entalpia de uma reação é possível o cálculo de propriedades como afinidade por próton e por elétron. Além disso, podem ser obtidas propriedades eletrônicas e estruturais de cálculos teóricos como densidade de carga, comprimento e ângulo de ligação.Os métodos compostos podem ser utilizados, por exemplo, na determinação de mecanismos de reações utilizando as propriedades termodinâmicas no cálculo da energia de ativação e de constantes de velocidade, 7-14 úteis em pesquisas que examinam em detalhes o mecanismo através do cálculo de constantes de velocidade para cada etapa da reação. 15,16 Outras propriedades muito estudadas são as afinidades por próton 17-23 e por elétron, 24-27 a acidez, 28 bem como a identificação da estrutura mais estável para um determinado isômero. 29,30 Compostos inorgânicos também podem ser explorados utilizando métodos compostos pelo cálculo do potencial de redução 31 em reações de óxido-redução.No trabalho de um químico, informações a respeito de entalpia de formação e energia de dissociação são muito importantes, existindo diversos estudos neste campo, onde os métodos compostos são amplamente utilizados.32-44 Outra aplicação interessante é no estudo do mecanismo em processos envolvidos em espectroscopia de massas. 45A variedade de aplicações utilizando métodos compostos vem aumentando tanto em trabalhos teóricos como em trabalhos experimentais, devido à sua praticidade, confiabilidade e precisão em prever parâmetros físico-químicos. Este trabalho avaliou alguns métodos compostos considerando-se a capacidade de reprodução de parâmetros experimentais e o ...

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A Quantum-Chemical Study of the C₂H₃F₂⁺ and C₂H₃Cl₂⁺ Isomers and Their Interconversion. CBS-QB3 Proton Affinities of Difluoroethenes and Dichloroethenes

Cited by 4 publications

References 49 publications

Ion chemistry of chloroethanes in air at atmospheric pressure

Ion chemistry of chloroethanes in air at atmospheric pressure

Isomerization and dissociation of C₂X₅⁺ and C₂X₄^+· ions (X = Cl, F) from chlorofluoroethanes in an ion trap mass spectrometer

Comparação entre métodos compostos no cálculo de afinidades por próton e elétron em sistemas moleculares

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A Quantum-Chemical Study of the C2H3F2+ and C2H3Cl2+ Isomers and Their Interconversion. CBS-QB3 Proton Affinities of Difluoroethenes and Dichloroethenes

Cited by 4 publications

References 49 publications

Ion chemistry of chloroethanes in air at atmospheric pressure

Ion chemistry of chloroethanes in air at atmospheric pressure

Isomerization and dissociation of C2X5+ and C2X4+· ions (X = Cl, F) from chlorofluoroethanes in an ion trap mass spectrometer

Comparação entre métodos compostos no cálculo de afinidades por próton e elétron em sistemas moleculares

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A Quantum-Chemical Study of the C₂H₃F₂⁺ and C₂H₃Cl₂⁺ Isomers and Their Interconversion. CBS-QB3 Proton Affinities of Difluoroethenes and Dichloroethenes

Isomerization and dissociation of C₂X₅⁺ and C₂X₄^+· ions (X = Cl, F) from chlorofluoroethanes in an ion trap mass spectrometer