Super acids. III. Protonation of alkanes and intermediacy of alkanonium ions, pentacoordinated carbon cations of CH5+ type. Hydrogen exchange, protolytic cleavage, hydrogen abstraction; polycondensation of methane, ethane, 2,2-dimethylpropane and 2,2,3,3-tetramethylbutane in FSO3H-SbF5

Oláh, George A.; Klopman, Gilles; Schlosberg, Richard H.

doi:10.1021/ja01040a029

Cited by 274 publications

(119 citation statements)

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“…Indeed, the activation energies for protolytic cracking of neopentane with formation of methane and tert-butyl cation in an HF-SbF 5 solution is equal to 21 kcal/mol [40] and only to 14 kcal/mol in an HSO3F-SbF 5 solution [41]. The activation energy of protolytic dehydrogenation of isobutane in the HF-SbFs system reported in Ref.…”

Section: Discussionmentioning

confidence: 91%

Quantumchemical study of the isobutane cracking on zeolites

Kazansky

Frash

Santen

1996

Applied Catalysis A: General

120

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Section: Discussionmentioning

confidence: 91%

Quantumchemical study of the isobutane cracking on zeolites

Kazansky

Frash

Santen

1996

Applied Catalysis A: General

120

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“…Strong interest on alkane protonation was provoked by the work of Olah (1,2), who investigated the reaction in superacid solutions. A three-center bond structure with C, symmetry (1 in Fig.…”

Section: Introductionmentioning

confidence: 99%

A theoretical investigation of energetics and structures of CH₅⁺(CH₄)_n clusters for n = 1–4

Fois¹,

Gamba²,

Simonetta³

1985

Can. J. Chem.

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“…The structure can be viewed as a proton inserted into one of the COH bonds of methane to form a 2eO3c bond between carbon and two hydrogen atoms. At the same time ready bond-to-bond (polytopal) proton migration makes it a rather fluxional molecule (19,20), the process involving extremely low barriers (17, 18).The five-coordinate methonium radical dication, CH 5 2ϩ• , was first observed in the gas phase by charge-stripping mass spectrometry by Proctor et al (9). Later the dication was also observed in the gas phase by Stahl et al (10) and by Holmes and coworkers (11).…”

mentioning

confidence: 99%

Comparison of structures and energies of CH ₅ ^2+• with CH ₄ ^+• and their possible role in superacidic methane activation

Rasul

Prakash²,

Oláh³

1997

Proc. Natl. Acad. Sci. U.S.A.

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Contrary to previous theoretical studies at the UHF͞6-31G* level, the methonium radical dication CH 5 2؉ is not a C s symmetrical structure with a 2eO3c bond but a C 2v symmetrical structure 1 with two 2eO3c bonds (at the UHF͞6-31G**, UMP2͞6-31G**, and UQCISD(T)͞6-311G** levels). The C s symmetrical structure is not even a minimum at the higher level of calculations. The four hydrogen atoms in 1 are bonded to the carbon atom by two 2eO3c bonds and the fifth hydrogen atom by a 2eO2c bond. The unpaired electron of 1 is located in a formal p-orbital (of the sp 2 -hybridized carbon atom) perpendicular to the plane of the molecule. Hydrogen scrambling in 1 is however extremely facile, as is in other C 1 cations. It is found that the protonation of methane to CH 5 ؉ decreases the energy for subsequent homolytic cleavage resulting in the exothermic (24.1 kcal͞ mol) formation of CH 4 ؉• . Subsequent reaction with neutral methane while reforming CH 5 ؉ gives the methyl radical enabling reaction with excess methane to ethane and H 2 . The overall reaction is endothermic by 11.4 kcal͞mol, but offers under conditions of oxidative removal of H 2 an alternative to the more energetic carbocationic conversion of methane.Activation of alkanes, main components of petroleum and natural gas, is an important area of chemistry. Consequently, knowledge of the parent methane cations and dications are of great significance. There have been many experimental and theoretical studies of methane cations and dications (1-3). The methane radical cation, CH 4 ϩ• is the parent ion in mass spectrometry. In an early PNDO study by Olah and Klopman (4) the structure of CH 4 ϩ• was found to have C 2v symmetry and can be considered as CH 2 ϩ• radical cation complexed with a hydrogen molecule involving a three-center two-electron (2eO3c) bond. The 2eO3c unit is perpendicular to the plane of the molecule. High level ab initio calculations are in agreement with this conclusion (ref. 5 and references therein). Isoelectronic boron analog of CH 4 ϩ• is neutral BH 4• , also has similar C 2v symmetrical structure (6). Methane dication CH 4 2ϩ have also been observed in the gas phase (7-11). Planar C 2v symmetrical structure is preferred for the CH 4 2ϩ as shown by Wong and Radom (12). Earlier calculations predicted (13, 14) a square planar D 4h symmetrical structure for the CH 4 2ϩ dication. The sp 2 -hybridized carbon atom of CH 4 2ϩ contains a 2eO3c bond and an empty p-orbital perpendicular to the plane of the molecule.CH 5 ϩ is considered the parent of nonclassical carbocations containing a five coordinate carbon atom. Recent extensive ab initio calculations by Marx and Parrinello (15) as well as by Müller and Kützelnigg (16) reconfirmed the preferred C s symmetrical structure (17, 18) for the CH 5 ϩ cation with a 2eO3c bond as originally suggested by Olah and coworkers (19,20). The structure can be viewed as a proton inserted into one of the COH bonds of methane to form a 2eO3c bond between carbon and two hydrogen atoms. At the same time ready ...

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Super acids. III. Protonation of alkanes and intermediacy of alkanonium ions, pentacoordinated carbon cations of CH5+ type. Hydrogen exchange, protolytic cleavage, hydrogen abstraction; polycondensation of methane, ethane, 2,2-dimethylpropane and 2,2,3,3-tetramethylbutane in FSO3H-SbF5

Cited by 274 publications

References 3 publications

Quantumchemical study of the isobutane cracking on zeolites

Quantumchemical study of the isobutane cracking on zeolites

A theoretical investigation of energetics and structures of CH₅⁺(CH₄)_n clusters for n = 1–4

Comparison of structures and energies of CH ₅ ^2+• with CH ₄ ^+• and their possible role in superacidic methane activation

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Super acids. III. Protonation of alkanes and intermediacy of alkanonium ions, pentacoordinated carbon cations of CH5+ type. Hydrogen exchange, protolytic cleavage, hydrogen abstraction; polycondensation of methane, ethane, 2,2-dimethylpropane and 2,2,3,3-tetramethylbutane in FSO3H-SbF5

Cited by 274 publications

References 3 publications

Quantumchemical study of the isobutane cracking on zeolites

Quantumchemical study of the isobutane cracking on zeolites

A theoretical investigation of energetics and structures of CH5+(CH4)n clusters for n = 1–4

Comparison of structures and energies of CH 5 2+• with CH 4 +• and their possible role in superacidic methane activation

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A theoretical investigation of energetics and structures of CH₅⁺(CH₄)_n clusters for n = 1–4

Comparison of structures and energies of CH ₅ ^2+• with CH ₄ ^+• and their possible role in superacidic methane activation