Stable Carbonium Ions Research Articles

Elucidating effect of acid strength on isomerization mechanisms of butene over solid acid catalysts in C4 alkylation

Understanding the effect of acid strength on butene isomerization mechanisms is essential in C4 alkylation process. Herein, the double bond, trans-cis, and skeleton isomerization mechanisms of butene over acid sites with different acid strengths were investigated utilizing density functional theory (DFT) calculations. It is demonstrated that the acid strength significantly affects the isomerization mechanisms of butene. The stability of carbonium ions as reaction intermediates follows the order: tert-butyl cation > cis-butyl cation > trans-butyl cation, which is more sensitive to acid strength than that of butoxide species. Therefore, the reaction pathways of double bond and trans-cis isomerizations changed with varying the acid strength. Based on the analysis of activation energy barriers, it is found that 1-butene and 2-butene can be easily converted into each other over strong acid site. Thus, for reactants, C4 alkylation has no selectivity to 1-butene and 2-butene over strong acid site, which is consistent with experimental study. This work provides mechanistic insights into the relationship among acid strength, type of butene, and quality of alkylate in the C4 alkylation process.

Stability of C3-C6 carbonium ions inside zeolites: A first principles study

Carbonium ions are crucial intermediates in catalysis as their nature can influence the reaction pathways. Understanding the stability of carbonium ions inside zeolites is very useful to understand the catalytic process. In this work, a series of C3-C6 carbonium ions were systematically studied inside zeolites SSZ-13, SAPO-34, Mordenite, SAPO-5, ZSM-5 and Faujasite, whose pores size are 3.72 Å, 3.72 Å, 4.70 Å, 4.92 Å, 7.35 Å and 7.42 Å, respectively. It was shown that the constituent of the zeolite as well as the confinement effect which is determined by the pore sizes are essential factors for the stability of cabonium ions. The stability of carbonium ions increases with the carbon number for silica based zeolites whereas it is not the case for aluminophosphate based zeolites. For small size carbonium ion C3H7+, the stability significantly increases with the pore size increases since the confinement effect from steric effect is little and the confinement effect from van der Waals, electrostatic interaction and electronic interaction etc. becomes dominant. Furthermore, C3H7+ is predicted to be a stable carbonium ion inside SAPO-5 due to the synergistic effect between the constituent of the zeolites and the confinement. In addition, it is found that the less hydrogen, the more stable for long chain carbonium ions due to the aromatic stabilization. This work provides useful information for zeolite catalyst designation and reaction mechanism discovery.

Substituent effects in chemical carcinogenesis: Chrysene and its methyl derivatives

Although chrysene and its other monomethyl derivatives are only marginal carcinogens, the 5-methyl derivative is highly carcinogenic. These compounds are examined within the framework of recent biochemical evidence regarding in vivo metabolic transformations, using theoretical reactivity indices. Several possible reasons are advanced for the high activity of the 5-methyl derivative: (1) the 5-methyl substituent blocks a K region, inhibiting a diversionary pathway, (2) the 5-methyl derivative is more effective in transforming from its 7,8-dihydrodiol to its dihydrodiol “bay region” epoxide form, and (3) this derivative forms a more stable carbonium ion.

Are carbenium and carbonium ions reaction intermediates in zeolite-catalyzed reactions?

The mechanism of acid-catalyzed hydrocarbon reactions such as skeletal isomerization, hydride transfer, alkylation, dehydrogenation and cracking in superacid media and over solid zeolites is analyzed and compared. In particular, the stability, rearrangements and nature (reaction intermediates or transition states) of trivalent carbenium ions and non-classical pentacoordinated carbonium ions in homogeneous and heterogeneous phase are discussed. It is concluded that both carbenium and carbonium ions may exist as true reaction intermediates in zeolite-catalyzed processes only when the positive charge is not easily accessible to framework oxygen atoms.

The influence of electronegativity on triangular three-centre two-electron bonds: the relative stability of carbonium ions, π-complex chemistry and the −2 hβ effect

Using the HMO approximation, bond energy equations for triangular three-centre, two-electron [3 c-2 e] bonded species AB 2 + (π-complexes) and the isomeric systems (AB−B +, BB−A +, BA−B + and A ++BB) are described. The electronegativity difference (Δ χ) between the atoms or groups A and B is assumed to be related to the difference ( h) in their Coulomb integrals and the variation of relative energies with electronegativity difference is explored. The bond energy curve for π-complexes is displaced relative to those of the two-centre, two-electron [2 c-2 e] bonded species and this displacement accounts for the significant influence of electronegativity difference on reactions proceeding via [3 c-2 e] bonded intermediates or transition states. The origin of the displacement of the bond energy versus electronegativity difference curve for the π-complexes is identified as a −2 hβ BB term in the bond energy equation. In contrast to [2 c-2 e] bonds, this term makes the influence of electronegativity difference on triangular [3 c-2 e] bonds directional, that is, the bond energies of AB 2 + and BA 2 + are different in contrast to those of AB and BA. A more electronegative atom A destabilises the [3 c-2 e] bond by removing electron density from the bonding interaction BB ( β BB) whereas a less electronegative atom A will strengthen the bond by increasing the electron density between the atoms B. Reactions involving [3 c-2 e] AB 2 + bonds are classified as homo- or heteroprocesses and the influence of electronegativity difference on these discrete transformations is discussed in terms of the contribution of h, h 2 and −2 hβ functions to differences in bond energy. The analysis is extended to π-complexes with back-donation and the equivalence of the description of onium ions using either two [2 c-2 e] bonds or two [3 c-2 e] bonds is demonstrated. Extension of the analysis to 2-norbornyl cations suggests that, due to the shape of the bond energy versus electronegativity difference curve, this cation exists within a window of stability between the alternative isomers. 1,2-Disubstituted norbornyl cations are used as a model of π-complexes and the influence of substituent effects on relative stability is explored using the AM1 method. After allowance for resonance and hyperconjugation effects, the results are found to be consistent with the general conclusions of the simple HMO model.

Kinetic Study of the Reaction of .ALPHA.-Bromoxylene and 2,4,6-Tribromophenol via Phase Transfer Catalysis at Low Alkalinity

The reaction of 2,4,6-tribromophenol and α-bromoxylenes (o-, p- and m-) catalyzed by tetrabutylammonium bromide was carried out in an alkaline solution of KOH of low concentration/organic solvent two-phase medium. The concentration of tetrabutylammonium 2,4,6-tribromophenoxide (ArOQ) is constant throughout the path of reaction while more than 98% of the catalyst exists as tetrabutylammonium 2,4,6-tribromophenoxide (ArOQ) in the organic phase. The mass transfer resistance of ArOQ between the two phases is negligible compared to the rate of organic-phase reaction. The reaction in the organic phase is a rate-determining step. A pseudo-first-order rate law is proposed to express the kinetic data. The effects of potassium hydroxide, organic solvents, agitation speed, amount of aqueous-phase reactant (2,4,6-tribromophenol), amount of catalyst, organic-phase reactant (α-bromoxylene), inorganic salts and temperature on the conversion are investigated in detail. It is found that the reaction rate is not well-correlated to the polarity of the organic solvent. The solvolysis effect, which concerns with the polarity and Lewis-base of the organic solvents, is used to explain the characteristics of the reaction satisfactorily at low alkaline concentration. The stability of carbonium ions of different α-bromoxylenes is used to explain their reaction rates satisfactorily.

Theoretical Study of Bimolecular Reactions between Carbenium Ions and Paraffins: The Proposal of a Common Intermediate for Hydride Transfer, Disproportionation, Dehydrogenation, and Alkylation

The mechanism of the bimolecular reactions of ethyl cation with ethane and propane and of s-propyl cation with ethane, propane, and isopentane is theoretically investigated by means of the B3PW91 density functional method. The study includes complete geometry optimization and characterization of the reactants, products, reaction intermediates, and transition states involved, calculation of the reaction enthalpies and activation energies for the different elemental steps, and obtainment of the equilibrium constants and relative reaction rate constants by means of transition state theory. It is found that the interaction of a carbenium ion with a saturated alkane always results in formation of a stable carbonium ion intermediate and that different intramolecular rearrangements of this common intermediate can explain the mechanism of acid-catalyzed hydrocarbon reactions, such as hydride transfer, disproportionation, dehydrogenation, and alkylation.

Benzylic carbonium ions as ultimate carcinogens of polynuclear aromatic hydrocarbons

Perturbational molecular orbital calculations were applied to a series of polynuclear aromatic hydrocarbons (PAH) to assess the energetics involved in generating electrophilic carbonium ions of two types, triol and benzylic carbonium ions. ΔE β , an index of carbonium ion formation and stability, was nearly always higher for benzylic carbonium ions attached to mesoanthracenic positions of PAHs than for terminal ring triol carbonium ions. Furthermore, the reactivity index N t for substitution reactions leading to benzylic carbonium ions was lowest in each molecule at the site corresponding to the most favorable ΔE β value. No similar relationship existed for ortholocalization energies of bonds at which addition reactions generate triol carbonium ions. Statistical analysis revealed that Iball indices for carcinogenicity showed higher correlation with both benzylic-relevant ΔE β and N t values than with triol carbonium ion ΔE β or ortholocalization energies. Various authors claim correlation between the energetics of triol carbonium ion generation and carcinogenicity, yet our observations along similar lines of reasoning demonstrate even stronger correlation and more favorable energetics for benzylic carbonium ions that require initial methylation at an exceptionally reactive center. Based on our calculations, we predict that animal tests, such as repeated application to mouse skin or repeated subcutaneous injection in mice or rats, should reveal benzylic carbonium ions arising from hydroxymethyl sulfate ester metabolites to be endowed with more complete carcinogenic potency than triol carbonium ions arising from dihydrodiol epoxide metabolites.

Solubilization of arsenic from gallium arsenide using aqueous suspensions of organic halides

AbstractThe solubilization of arsenic in solid gallium arsenide by aqueous solutions/suspensions of organic halides is described. Although arsenic is removed from gallium arsenide surfaces, excess quantities of gallium are not found in the solution. The abilities of the organic halide to solubilize arsenic decreases as follows: C2H5Br> CH3I> 2‐C3H7I> 1‐C3H7I> 2‐C4H9Br> CH2CHCH2I> 2‐C3H7Br≃ 1‐C4H9Br.The results correlate with a combination of organic halide solubility, bond enthalpy and carbonium ion stability factors. Other parameters investigated using gallium arsenide and iodomethane include concentration, physical state of the arsenide, pH, role of oxygen and role of light.

Importance of electronic geminal interactions in solvolysis reactions. Application to the determination of the .alpha.-silyl effect on carbonium ion stability

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTImportance of electronic geminal interactions in solvolysis reactions. Application to the determination of the .alpha.-silyl effect on carbonium ion stabilityYitzhak Apeloig, Rivka Biton, and Awad Abu-FreihCite this: J. Am. Chem. Soc. 1993, 115, 6, 2522–2523Publication Date (Print):March 1, 1993Publication History Published online1 May 2002Published inissue 1 March 1993https://doi.org/10.1021/ja00059a065RIGHTS & PERMISSIONSArticle Views143Altmetric-Citations46LEARN 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 (327 KB) Get e-Alerts Get e-Alerts

Reactions of ferrocene and nickelocene with some stable carbonium ions

The reaction of ferrocene and tropylium hexafluorophosphate yields ferrocenyltropylium PF6, which crystallizes in the monoclinic space group P21/C (a = 9.7858(10) Å, b = 16.3692(24) Å, c = 10.901(4) Å, β = 113.030(18)°, Z = 4, T = 27 °C, V = 1607.0(7) Å3, Rf = 0.091, Rw = 0.040) for 102 parameters and 929 observed (I > 2.5 σ(I)) out of 2087 total measured reflections. The reaction of nickelocene and triphenylmethyl tetrafluoroborate yields triphenylmethylcyclopentenyl cyclopentadienyl nickel tetrafluoroborate, which crystallizes in the monoclinic space group P21/n (a = 11.0306(19) Å, b = 14.078(4) Å, c = 17.117(4) Å, β = 101.134(18)°, Z = 4, T = 27 °C, V = 2608.0(11) Å3, Rf = 0.091, Rw = 0.035) for 147 parameters and 1334 out of 3361 measured reflections.

.gamma.-Silicon stabilization of carbonium ions in solvolysis. 3. Solvolysis of 4-(trimethylsilyl)-3-methyl-2-butyl p-bromobenzenesulfonates

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXT.gamma.-Silicon stabilization of carbonium ions in solvolysis. 3. Solvolysis of 4-(trimethylsilyl)-3-methyl-2-butyl p-bromobenzenesulfonatesV. J. Shiner Jr., Mark W. Ensinger, and John C. HuffmanCite this: J. Am. Chem. Soc. 1989, 111, 18, 7199–7205Publication Date (Print):August 1, 1989Publication History Published online1 May 2002Published inissue 1 August 1989https://doi.org/10.1021/ja00200a045RIGHTS & PERMISSIONSArticle Views535Altmetric-Citations27LEARN 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 (927 KB) Get e-Alerts Get e-Alerts

ChemInform Abstract: Precise Determination of Stabilities of Primary, Secondary, and Tertiary Silicenium Ions from Kinetics and Equilibria of Hydride‐Transfer Reactions in the Gas Phase. A Quantitative Comparison of the Stabilities of Silicenium and Carbonium Ions in the Gas Phase.

ChemInform Abstract: Precise Determination of Stabilities of Primary, Secondary, and Tertiary Silicenium Ions from Kinetics and Equilibria of Hydride‐Transfer Reactions in the Gas Phase. A Quantitative Comparison of the Stabilities of Silicenium and Carbonium Ions in the Gas Phase.

Precise determination of stabilities of primary, secondary, and tertiary silicenium ions from kinetics and equilibria of hydride-transfer reactions in the gas phase. A quantitative comparison of the stabilities of silicenium and carbonium ions in the gas phase

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPrecise determination of stabilities of primary, secondary, and tertiary silicenium ions from kinetics and equilibria of hydride-transfer reactions in the gas phase. A quantitative comparison of the stabilities of silicenium and carbonium ions in the gas phaseSeung Koo Shin and J. L. BeauchampCite this: J. Am. Chem. Soc. 1989, 111, 3, 900–906Publication Date (Print):February 1, 1989Publication History Published online1 May 2002Published inissue 1 February 1989https://doi.org/10.1021/ja00185a017RIGHTS & PERMISSIONSArticle Views145Altmetric-Citations40LEARN 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 (910 KB) Get e-Alerts Get e-Alerts

Carbonium ion stabilization by (η 5-cyclopentadienyl)dicarbonylnitrosylchromium; a 1H and 13C NMR study

the 1H and 13C NMR spectra of a series of (η 5-cyclopentadienyl)dicarbonylnitrosylchromium-substituted carbonium ions have been determined. These data suggest that the same mechanism is responsible for the stabilization of carbonium ions by (η 5-cyclopentadienyl)dicarbonylnitrosylchromium as is operational in the analogous ferrocene and cymantrene complexes.

The mechanism of chain growth in the Fischer-Tropsch hydrocarbon synthesis

It is proposed that the slow step in chain growth during the Fischer-Tropsch hydrocarbon synthesis is the formation of an adsorbed ethylidene species from two adsorbed methylenes. Addition of a further methylene species gives a diadsorbed C3H6 entity, which leads to a singly attached carbonium ion. A 1,2 hydrogen shift then forms a methyl substituted ethylidene species, which is available for further polymerisation. Further hydrogen shift may occur, yielding an olefin and terminating the chain growth. The extent of chain branching is dictated by the relative stability of secondary and primary carbonium ions, as previously proposed by McCandlish, (J. Catalysis 83 (1983) 362).

ChemInform Abstract: Hydrocarbation‐Formation of Diiron μ‐Alkylidyne Complexes from the Addition of the Carbon‐Hydrogen Bond of a μ‐Methylidyne Complex Across Alkenes.

AbstractThe cationic methylidyne Complex (I) with a relatively stable carbonium ion reacts with alkenes (II) and (V) to produce the alkylidyne Complexes (III) and (VI).

The mechanism of aromatic transalkylation in ZSM-5

The ZSM-5-catalyzed transalkylation of ethylbenzene, which yields benzene and diethylbenzenes, occurs by acid-catalyzed cleavage of the ethyl group followed by addition of the ethyl group to another ethylbenzene. Xylenes transalkylate much more slowly because methyl groups are more difficult to cleave than ethyl groups due to their decreased carbonium ion stability. When a mixture of xylenes and ethylbenzene reacts, diethylbenzenes are produced preferentially to dimethylethylbenzenes if the ZSM-5 crystallites are in a size range that allows the disubstituted benzenes to diffuse out of the zeolite crystallites much faster than the trisubstituted benzenes. The dimethylethylbenzenes (produced by ethyl group addition to the xylenes) diffuse so slowly from the larger crystallites that the added ethyl group is cleaved and xylene exits, apparently unreacted.

.gamma.-Silicon stabilization of carbonium ions in solvolysis. I. Solvolysis of cis- and trans-3-(trimethylsilyl)cyclohexyl p-bromobenzenesulfonates

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXT.gamma.-Silicon stabilization of carbonium ions in solvolysis. I. Solvolysis of cis- and trans-3-(trimethylsilyl)cyclohexyl p-bromobenzenesulfonatesV. J. Shiner, Mark W. Ensinger, and George S. KrizCite this: J. Am. Chem. Soc. 1986, 108, 4, 842–844Publication Date (Print):February 1, 1986Publication History Published online1 May 2002Published inissue 1 February 1986https://doi.org/10.1021/ja00264a050RIGHTS & PERMISSIONSArticle Views239Altmetric-Citations42LEARN 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 (458 KB) Get e-Alerts Get e-Alerts

Stabilities of Carbonium-Ions. IV. Steric Effects in the Solvolysis of Substituted Diphenylmethyl Chlorides

The replacement of ortho-hydrogen atoms by methyl groups in diphenylmethyl chloride has three distinguishable results upon the rate of solvolysis . Firstly, the alkyl groupactivates by its electronic effect; secondly, steric interactions diminish all observed substituent effects regardless of the position of the substituent in the aryl system; and thirdly, steric acceleration of the solvolysis can be seen in the rate of reaction of bis (2,6-dimethylphenyl)methyl chloride. The ortho-methyl substituents inhibit the formation of the planar transition state necessary to allow the greatest resonance stabilization by the aryl substituents of the incipient carbocation. Greater degrees of twist are reflected both in the variations in the rates of solvolysis of the poly(orthomethyl ) diphenylmethyl chlorides and in the consistent fall in the value of p+ with successive ortho-substitution.