Molecular motion of benzene, n-hexane, and cyclohexane in potassium zeolite L studied by deuterium NMR

Journal Article · Thu Aug 24 04:00:00 EDT 1989 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100354a044· OSTI ID:7171276

Silbernagel, B G; Garcia, A R; Newsam, J M; Hulme, R ^[1]

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1. Exxon Research and Engineering Co., Annandale, NJ (USA)

The molecular motions of perdeuterated benzene, n-hexane, and cyclohexane sorbed at loading levels of 1 molecule per channel lobe (or, equivalently, per unit cell) in potassium zeolite L have been examined by {sup 2}H nuclear magnetic resonance (NMR) for 100 K {le} T {le} 350 K. Benzene (C{sub 6}D{sub 6}) gives a broad signal with, for T < {approx} 150 K, a quadrupolar splitting of half of the static value, interpreted in terms of rapid reorientation in the molecular plane. This mode of motion is consistent with the location of benzene in capping positions above channel wall site potassium cations observed at 78 K by powder neutron diffraction. For temperatures above {approx} 250 K, a less broad component (interpreted as indicating activated benzene site hopping) develops. Sorbed n-hexane (C{sub 6}H{sub 14}) also shows no evidence for isotropic motion. Two distinct spectral components, associated respectively with the methyl and methylene deuterons, are observed. The magnitudes of the {sup 2}H quadrupolar coupling strengths can be interpreted solely in terms of torsional rotations about the carbon-carbon bonds. The temperature dependence of the {sup 2}H spin-lattice relaxation processes suggests an activation energy of {approx} 2 kcal mol{sup {minus}1} for these C-C bond rotations, consistent with earlier studies of bond rotation in alkanes. Sorbed cyclohexane (C{sub 6}D{sub 12}) shows a transition in the dynamical behavior (on the time scale of the {sup 2}H NMR experiment) in the vicinity of 280 K. Close to 280 K , a narrow signal is observed consistent with effectively isotropic reorientations, but both above and below 280 K there is a significant residual quadrupole interaction. The narrow component decreases rapidly with temperature, becoming unobservable below 230 K.

• OSTI ID: 7171276
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 93:17; ISSN JPCHA; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020000 -- Petroleum
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400000* -- Chemistry
400102 -- Chemical &amp; Spectral Procedures
400202 -- Isotope Effects
Isotope Exchange
&amp; Isotope Separation
ALKANES
AROMATICS
BENZENE
CYCLOALKANES
CYCLOHEXANE
DATA
DATA ANALYSIS
EXPERIMENTAL DATA
HEXANE
HYDROCARBONS
INFORMATION
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOTOPE EFFECTS
MATERIALS
MEASURING INSTRUMENTS
MEASURING METHODS
MINERALS
MOBILITY
NUMERICAL DATA
ORGANIC COMPOUNDS
ZEOLITES