Proton affinities of some polyfluoroalkanes in comparison to the unsubstituted alkanes. The estimation of the proton affinities of polytetrafluoroethylene and polyethylene by applying theoretical methods

Otto, André; Prescher, Dietrich; Gey, E.; Schrader, Sigurd

doi:10.1016/s0022-1139(99)60355-4

Cited by 8 publications

(6 citation statements)

References 33 publications

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“…But for polymer materials with traps, E  is the trap depth. The C-C bond breaking energy is reported to be about 3.8 eV [39], and our experimental results show that the dc breakdown strength E dc is 354kV/mm for sample LDPE-Al-0.5. x is estimated to be 10.7nm according to equation (1).…”

Section: Influence Of Free Volume Onmentioning

confidence: 48%

Influence of hydrostatic pressure on dielectric properties of polyethylene/aluminum oxide nanocomposites

Wang

et al. 2014

IEEE Trans. Dielect. Electr. Insul.

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The effect of hydrostatic pressure on the dielectric characteristics of polyethylene/aluminum oxide nanocomposites is reported in the present work. Nanocomposite specimens with a thickness of 0.2mm were placed in a hydrostatic press at pressures ranging from 50 to 200 MPa. Then, ac and dc breakdown and dielectric spectroscopy measurements were carried out on the original and treated specimens. In comparison to the dielectric properties of the original specimens, the results of the treated specimens demonstrate some interesting dielectric behaviors. For example, the breakdown strengths of the treated specimens are enhanced, and the permittivity and dielectric loss are reduced after the hydrostatic pressure treatments. It is found that the movements of molecular chains and polar groups are restricted especially in the interfacial region, leading to the reduction in permittivity and dielectric loss of specimens after hydrostatic pressure treatment. The improvement in breakdown properties is due to the reduction in free volume or a more uniform size distribution of free volume in the nanocomposites after hydrostatic pressure treatments.Index Terms -hydrostatic pressure, interfacial region, free volume, breakdown, nanocomposites.

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Section: Influence Of Free Volume Onmentioning

confidence: 48%

Influence of hydrostatic pressure on dielectric properties of polyethylene/aluminum oxide nanocomposites

Wang

et al. 2014

IEEE Trans. Dielect. Electr. Insul.

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“…Proponium and butonium ions have been recently studied computationally by Mota and co-workers, ,, 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. ,,,− Several computational studies have investigated the catalytic carbonium initiation mechanism directly, by attempting to model actual catalytic events involving carbonium ion formation, ,,,− ,− and although these models all suffer from incomplete treatment of long-range effects, they have resulted in one intriguing suggestionthat carbonium ions in condensed phases are not intermediates but transition states . Three of the outstanding questions regarding the carbonium initiation mechanism are the following: why does the proton attack some alkanes but not others, where on an alkane does the catalytic proton attack, and how exactly do these carbonium ions produce carbenium ions?…”

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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“…25,26 Solutionphase carbonium ions have never been directly detected, although one was first proposed 27 in 1952 and the idea has been greatly popularized by Olah, following his initial reactions of alkanes with superacids, 2,[28][29][30] and by Haag and Dessau, who incorporated them into catalytic cracking mechanisms. 5,31 Many theoretical chemistry studies of these intermediates have appeared; the ones since 1997 have studied these species either in isolation [32][33][34][35][36][37][38][39][40][41][42][43][44][45] or in contact with small catalyst models. [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60] Theoretical simulations of alkane reactions involving carbonium ions have been reviewed recently, [61][62][63] but the current theoretical knowledge of the H + + C x f C x-y + C y + reaction mechanism is still significantly inadequate.…”

Section: Introductionmentioning

confidence: 99%

“…Carbonium ions (protonated alkanes, acyclic C x H 2 x +3 + ) are gas-phase ions of very short lifetimes, originally detected and studied via mass spectrometry experiments. − Only two gas-phase infrared spectra have been reported to date. , Solution-phase carbonium ions have never been directly detected, although one was first proposed in 1952 and the idea has been greatly popularized by Olah, following his initial reactions of alkanes with superacids, ,− and by Haag and Dessau, who incorporated them into catalytic cracking mechanisms. , Many theoretical chemistry studies of these intermediates have appeared; the ones since 1997 have studied these species either in isolation − or in contact with small catalyst models. − …”

Section: Introductionmentioning

confidence: 99%

A Mechanistic Study of the Brønsted-Acid Catalysis ofn-Hexane → Propane + Propene, Featuring Carbonium Ions

2002

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A hypothetical five-step catalytic cycle for Brønsted-mediated fission of an all-trans n-alkane was examined using density functional theory. Optimized geometries and transition states were determined for catalystreactant complexes, using three different monodentate catalyst ions (NH 4 + , H 3 O + , and H 2 F + ). Despite the wide variety of catalyst acidities, protonated hexane appears as an intermediate (not a transition state) in each case. The protonated cyclopropane structure is the most likely initial form of the dissociated product ion. The predicted intermediates were seen to vary with catalyst acidity. The complete energy profiles of this model catalytic cycle are provided and fitted to a cosine expansion, which allows for generation of the energy profile for any Brønsted catalyst and any n-alkane only on the basis of the proton affinities of the n-alkane and the conjugate base of the catalyst. Remarks on the applicability to zeolites and ionic liquid catalysts are given.

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Proton affinities of some polyfluoroalkanes in comparison to the unsubstituted alkanes. The estimation of the proton affinities of polytetrafluoroethylene and polyethylene by applying theoretical methods

Cited by 8 publications

References 33 publications

Influence of hydrostatic pressure on dielectric properties of polyethylene/aluminum oxide nanocomposites

Influence of hydrostatic pressure on dielectric properties of polyethylene/aluminum oxide nanocomposites

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

A Mechanistic Study of the Brønsted-Acid Catalysis ofn-Hexane → Propane + Propene, Featuring Carbonium Ions

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