Dynamics of n-Hexane Inside Silicalite, as Studied by 2H NMR Full article
| Journal |
The Journal of Physical Chemistry B
ISSN: 1520-6106 , E-ISSN: 1520-5207 |
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| Output data | Year: 2003, Volume: 107, Number: 29, Pages: 7095-7101 Pages count : 7 DOI: 10.1021/jp0300501 | ||||||
| Tags | Activation energy; Adsorption; Anisotropy; Chemical bonds; Conformations; Diffusion; Isomerization; Molecular dynamics; Molecular orientation; Nuclear magnetic resonance spectroscopy; Reduction; Silicon compounds | ||||||
| Authors |
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| Affiliations |
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Funding (2)
| 1 | Russian Foundation for Basic Research | 00-03-22002 |
| 2 | International Association for the Promotion of Co-operation with Scientists from the New Independent States of the Former Soviet Union | 96-1177 |
Abstract:
Perdeuterated n-hexane, adsorbed in silicalite, has been found to exhibit a 2H NMR spectrum that represents a superposition of three Pake-powder patterns. Two Pake-powder patterns, with the spectral parameters CQ = 23.5 kHz and η = 0 and CQ = 30.1 kHz and η = 0 (CQ represents quadrupole constants and η is the asymmetry parameter), belong to different methylene groups and one powder pattern, with CQ = 7.0 kHz and η = 0.7, arises from the methyl groups. The observed line shapes have been concluded to arise from the fast anisotropic translational and rotational motions of the alkane in the silicalite channels. The reduction of the quadrupole constants, in comparison to that in rigid n-hexane, and the appearance of an asymmetry parameter for the methyl groups have been interpreted in terms of three modes of motion exhibited by n-hexane inside the channel system: (a) rotation of the molecule about the channel axis; (b) trans/gauche conformational isomerization around nonterminal C−C bonds and rotation of the methyl groups around terminal C−C bonds; and (c) fast interchange of the adsorbed molecules between both straight and zigzag channels and along zigzag channels with an effective angle of ∼90° between adjacent sites of the molecule location during successive jumps. The proportion percentage of trans/gauche conformations is estimated to be 78/22, which exceeds that in gas phase or liquids. This demonstrates that constraining effects of the narrow silicalite pore walls retain the molecules in a more elongated conformation, compared to that in a gas phase or liquid. The rotation of a methyl group around a terminal C−C bond has been estimated to occur with a characteristic time of ∼40 ps at 300 K and an activation energy of 9.4 kJ/mol. The reorientation of methylene groups, corresponding either to conformational isomerization or to translational diffusion, occurs 1 order of magnitude slower, with a characteristic time of ∼300 ps and an activation energy of 7.5 kJ/mol.
Cite:
Stepanov A.G.
, Shubin A.A.
, Luzgin M.V.
, Shegai T.O.
, Jobic H.
Dynamics of n-Hexane Inside Silicalite, as Studied by 2H NMR
The Journal of Physical Chemistry B. 2003. V.107. N29. P.7095-7101. DOI: 10.1021/jp0300501 WOS Scopus РИНЦ ANCAN OpenAlex
Dynamics of n-Hexane Inside Silicalite, as Studied by 2H NMR
The Journal of Physical Chemistry B. 2003. V.107. N29. P.7095-7101. DOI: 10.1021/jp0300501 WOS Scopus РИНЦ ANCAN OpenAlex
Dates:
| Submitted: | Jan 14, 2003 |
| Accepted: | Apr 22, 2003 |
| Published print: | Jul 1, 2003 |
Identifiers:
| Web of science: | WOS:000184242600025 |
| Scopus: | 2-s2.0-0042705220 |
| Elibrary: | 13429001 |
| Chemical Abstracts: | 2003:491626 |
| Chemical Abstracts (print): | 139:179769 |
| OpenAlex: | W1988706956 |