The n-Butonium Cation (n-C4H11+):  The Potential Energy Surface of Protonated n-Butane

Esteves, Pierre M.; Alberto, Gabriel G. P.; Ramı́rez-Solı́s, A.; Mota, Cláudio J. A.

doi:10.1021/jp001152j

Cited by 27 publications

(36 citation statements)

References 43 publications

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“…12 From the structural point of view, the protonated methylcyclopropane is similar to the one formed for the corner-protoned cyclopropane. 24 The topology of the charge density in complex 14 shows only three BCPs between C-C bonds.…”

Section: D(c-h*) D(c-c)mentioning

confidence: 80%

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Ab Initio Topological Analysis of the Electronic Density inn-Butonium Cations and Their van der Waals Complexes

et al. 2002

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In this work, the topology of the ab initio electronic density charge, using the theory of atoms in molecules (AIM), developed by Bader, is studied for the n-C 4 H 11 + species, the protonated n-butane. The electronic delocalization that operates through the σ bonds in saturated molecules and specifically in protonated alkanes is studied by means of analysis of the charge density and the bond critical points. This analysis is used in order to establish a relationship among the parameters that determine the stability order found for the different species and relate them with the carbonium ions structure. Comparing these results with the i-C 4 H 11 + allow us to study the nature of the 3c-2e bonds in alkanes in greater detail, permitting the description on the σ basicity and reactivity scales in terms of structural parameters of the carbonium ions.

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Section: D(c-h*) D(c-c)mentioning

confidence: 80%

“…The stability of the de van der Waals complexes decreased in the order 12 > 15 > 14 > 13. 12 Results and Discussion: n-C 4 H 11 + Cations. Table 1 shows the most significant topological local properties at the bond critical points (3, -1) for structures 1-3 corresponding to the 1-H-n-butonium cations.…”

Section: Methods and Calculation Detailsmentioning

confidence: 99%

Ab Initio Topological Analysis of the Electronic Density inn-Butonium Cations and Their van der Waals Complexes

et al. 2002

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“…Two of the three general isomers of C 2 H 7 + ion have been detected in the gas phase. 37 Proponium and butonium ions have been recently studied computationally by Mota and co-workers, 22,38,39 demonstrating multiple possible geometries for protonation, as well as providing useful energetics. Calculations on larger carbonium ions have been limited in accuracy and/or scope.…”

Section: Introductionmentioning

confidence: 99%

Properties of C−C Bonds inn-Alkanes: Relevance to Cracking Mechanisms

Hunter

East

2002

J. Phys. Chem. A

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The slight variations among the proton affinities and bond strengths of the C-C bonds in straight-chain n-alkanes have been determined to 1 kcal mol -1 accuracy for the first time, using computational quantum chemistry. Four computational methods (B3LYP, MP2, CCSD(T), and G2) were used to study n-alkanes (up to C 20 H 42 with B3LYP), including computations on the related alkyl radicals, carbenium ions, and carbonium ions. The proton affinities of the C-C bonds vary from 142 to over 166 kcal mol -1 , are highest for the center C-C bond, and decrease monotonically toward the end bonds. Bond strength, unlike proton affinity, is very constant (88 kcal mol -1 ), except for the R and bonds (89 and 87 kcal mol -1 , respectively). For thermal cracking, the results suggest that the most favored initiation step is the breaking of the bond of the alkane to create an ethyl radical. For Bronsted-acid-catalyzed cracking of straight-chain paraffins, if the initiation mechanism is via carbonium ions, then the results indicate that the central C-C bonds of n-alkanes will be most attractive to the Bronsted proton. However, for direct protolysis (Bronsted-mediated fission) of an n-alkane via a carbonium intermediate, the net exothermicities do not strongly discern among the C-C bonds. Trends in molecular geometry and infrared spectra features are also presented, and a signature IR band is predicted for carbonium ions that should aid in their identification.

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“…This type of reaction may involve extremely low activation barriers, as demonstrated in previous work of the group at higher level of calculations. 30,31 The hydride transfer from isopentane to 1-adamantyl cation is endothermic by 6.9 kcal mol -1 . Alternatively, if we consider the opposite reaction (DH o = -6.9 kcal mol -1 ), the calculations are in good agreement with previous gasphase equilibrium measurements from mass spectrometry, which indicated an exothercimicity of 7.6 kcal mol -1 for the HT between tert-butyl cation and adamantane, a similar system.…”

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A theoretical study of the hydride transfer between 1-Adamantyl cation and isopentane

Oliveira¹,

Rosenbach²,

Santos³

et al. 2010

J. Braz. Chem. Soc.

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Foi realizado um estudo teórico da transferência de hidreto entre o cátion 1-adamantila e isopentano, usando a teoria do funcional da densidade em nível PBE1PBE/6-31G (d,p). Os resultados indicaram que há formação de um íon carbônio como intermediário, que é mais estável que os complexos de van der Waals entre os íons carbênios e os alcanos. Os fatores entrópicos são bastante importantes e sobrepujam o termo entálpico à temperatura ambiente.A density functional teory study of the hydride transfer between 1-adamantyl cation and isopentane has been performed at the PBE1PBE/6-31G(d,p) theoretical level. The results indicate that a carbonium ion is involved as intermediate and is more stable than the van der Waals complexes between the carbenium ions and the alkanes. Entropic factors are important and overcome the enthalpic term at room temperature. Keywords: hydride transfer, carbocations, adamantane, isopentane IntroductionIntermolecular or bimolecular hydride transfer (HT) is a crucial step in acid-catalyzed hydrocarbon transformations. This reaction is involved in the propagation of the catalytic cycle of cracking 1,2 and alkylation 3 of hydrocarbons, as well as in the formation of aromatic hydrocarbons 4 in gasoline and coke, 5,6 which are carbonaceous materials deposit over the catalyst surface that may lead to loss of activity. Conceptually, HT involves the bimolecular transfer of a hydride from an alkane to a carbenium ion (Scheme 1). R⊕ + R'-H → R-H + R'⊕ Scheme 1. Schematic representation of hydride transfer reactions.In the gas phase, HT is much slower than proton transfer 7 and shows a negative temperature dependence. [8][9][10] The reaction is believed to occur via formation of a "tight" complex, 11,12 whose structure may resemble a carbonium ion, 13 formed by the interaction of the empty p-orbital of a carbenium ion with the C-H bond of the alkane. The reaction is used 14,15 to assess the carbenium ion stability in the gas phase.In condensed phase, especially on zeolites and other solid acid catalysts, there are few studies regarding hydride transfer. 16,17 Product distribution obtained from bimolecular alkane reactions is potentially interesting for the evaluation of the HT capability of solid acids. However, the validity of the results depends on the system chosen as model reaction. Indeed, variation of the hydride acceptor seems to affect the rates of hydride transfer to a considerably greater extent, than an equal change of the thermodynamic driving force caused by variation of the hydride donor. 18 In addition, some systems involve simultaneous reactions competing with HT, and may significantly affect the interpretation of the results.The 1-adamantyl cation is a stable species 19 and can be synthesized from the 1-adamantanol and fluorosulfonic acid-antimony pentafluoride. 20 On the zeolite surface, this species can be also generated from its halide. 21 In addition de Oliveira et al. 2181 Vol. 21, No. 12, 2010 to the stabilization by sC-C bond hyperconjugation, the 1-adamantyl cation has a cage ...

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The n-Butonium Cation (n-C₄H₁₁⁺): The Potential Energy Surface of Protonated n-Butane

Cited by 27 publications

References 43 publications

Ab Initio Topological Analysis of the Electronic Density inn-Butonium Cations and Their van der Waals Complexes

Ab Initio Topological Analysis of the Electronic Density inn-Butonium Cations and Their van der Waals Complexes

Properties of C−C Bonds inn-Alkanes: Relevance to Cracking Mechanisms

A theoretical study of the hydride transfer between 1-Adamantyl cation and isopentane

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