A deuterium NMR study of guest molecular dynamics of acetone in two organic inclusion compounds

1995 ◽  
Vol 73 (12) ◽  
pp. 2196-2207 ◽  
Author(s):  
Paul S. Sidhu ◽  
Jason Bell ◽  
Glenn H. Penner ◽  
Kenneth R. Jeffrey
Keyword(s):  
Molecular Dynamics ◽  
Inclusion Compounds ◽  
Nmr Spectra ◽  
Guest Molecule ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Deuterium Nmr ◽  
Spin Lattice ◽  
Nmr Study

Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times (T1) are used to investigate the dynamics of the guest molecule, acetone, in tris(5-acetyl-3-thienyl)methane (TATM) and cyclotriveratrylene (CTV) inclusion compounds. 13C CPMAS powder NMR spectra were obtained for each clathrate, to verify inclusion. In acetone: TATM, the guest molecule is undergoing twofold reorientation about the CO bond, exchanging the two methyl groups. An activation energy of 20 (± 1.4) kJ/mol, for the two-site jump motion, was found, independently, from deuterium NMR spectra an T1 measurements. Acetone in CTV performs the same type of motion as acetone in TATM. Activation energies of 25.0 (± 3.2) kJ/mol and 24.1 (± 0.5) kJ/mol were determined using the same two techniques. both inclusion compounds, the rate of methyl rotation within the acetone molecule is greater than 108 Hz even at the lowest temperature measured (84 K). Analytical expressions for the spin-lattice relaxation time (T1), for a twofold jump, were derived. Calculated values of the effective quadrupolar coupling constant and T1min for the guests agree very well with the experimental data. The 84 K spectrum of acetone:TATM unexpectedly shows some asymmetry, the origin of which is discussed. Finally, these two clathrates are compared to the recently examined acetone: tri-ortho-thymotide inclusion compound. Key words: inclusion compounds, deuterium NMR, solid state NMR spectroscopy, molecular dynamics.

Molecular Dynamics in the Solid Trimethylamine-Borane Complex: A Deuterium NMR Study

1995 ◽  
Vol 50 (1) ◽  
pp. 81-89 ◽  
Author(s):  
Glenn H. Penner ◽  
Baiyi Zhao ◽  
Kenneth R. Jeffrey
Keyword(s):  
Molecular Dynamics ◽  
Variable Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Activation Energies ◽  
Spin Lattice Relaxation ◽  
Deuterium Nmr ◽  
Molecular Orbital Calculations ◽  
Spin Lattice ◽  
Nmr Study

Abstract The molecular dynamics of solid (CH3)3NBH3 is investigated by deuterium NMR spectroscopy. Variable temperature lineshape analyses yield activation energies of 27 ± 3, 19 ± 2, and 12.5 ± 2 kJ/mol for -CH3, -N(CH3)3 and -BH3 rotation, respectively. Analysis of the temperature depen­ dence of the spin-lattice relaxation times, T1 , gives activation energies of 33 ± 3, 15 ± 1.5, and 14 ± 1.5 kJ/mol, respectively. Direct comparison of rotational exchange rates (from lineshape simu­ lations) an of rotational correlation times (from T1 analyses) for -N(CH3)3 and -BH3 rotation indicate that the two motions are correlated in solid (CH3)3NBH3 and together constitute a whole molecule reorientation about the N-B bond. This is supported by an internal rotational barrier of 18.0 kJ/mol for-BH3 rotation, obtained from ab initio molecular orbital calculations at the MP2/6-31G* level.

A deuterium NMR study of guest molecular dynamics in tris(5-acetyl-3-thienyl) methane inclusion compounds

1996 ◽  
Vol 74 (10) ◽  
pp. 1784-1794 ◽  
Author(s):  
Paul S. Sidhu ◽  
Jason Bell ◽  
Glenn H. Penner ◽  
Kenneth R. Jeffrey
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Inclusion Compounds ◽  
Nmr Spectra ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Deuterium Nmr ◽  
Spin Lattice ◽  
Methyl Rotation

Deuterium nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times (T1) are used to investigate the guest molecular dynamics of tris(5-acetyl-3-thienyl) methane (TATM) inclusion compounds. The seven guests: acetonitrile, nitromethane, dimethyl sulfoxide, benzene, mesitylene, ortho-xylene, and para-xylene show a wide variety of motional behaviour. The reorientation of acetonitrile in TATM and nitromethane in TATM were both modelled as precession on a cone, the base of which is more elliptical in shape for nitromethane, as would be expected considering their molecular symmetries. DMSO in TATM does not undergo any reorientation other than methyl rotation at the temperatures investigated. At low temperatures, the 2H lineshape and the deuterium spin-lattice relaxation time both depend on the rate of methyl rotation. Activation barriers of 11.7 (±0.4) kJ/mol and 11.2 (±0.5) kJ/mol were found from the two techniques, respectively. Benzene undergoes sixfold reorientation about the principal molecular axis; however, the rate is still greater than 108 Hz down to 113 K. The spin-lattice relaxation time profile does not reach a minimum on decreasing temperature to 112 K, while the slope of this plot provides an activation energy of 4.1 (±0.4) kJ/mol for the sixfold reorientation. The deuterium NMR spectra of mesitylene-d9 in TATM can be simulated using a model where the guest occupies two different sites in the TATM lattice, with the guest molecules performing in-plane C3 rotation either very rapidly (k > 108 Hz) or very slowly (k < 103 Hz), with the relative populations of each changing with temperature. Another model proposed suggests the possibility that there is a continuous distribution of motional rates, the median of which is increasing with temperature. This second model is more realistic; however, too many parameters are present to consider a detailed fit. Finally, both o-xylene and p-xylene are rigidly held in the TATM clathrate, while rotation of the methyl groups is rapid. Key words: inclusion compounds, solid state deuterium NMR spectroscopy, molecular dynamics.

1H NMR Study of Molecular Motions in Thiourea Pyridinium Halide Inclusion Compounds

2003 ◽  
Vol 58 (11) ◽  
pp. 638-644 ◽  
Author(s):  
M. Grottel ◽  
A. Pajzderska ◽  
J. Wasicki
Keyword(s):  
Inclusion Compounds ◽  
Symmetry Axis ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Hindered Rotation ◽  
Pyridinium Cation ◽  
Spin Lattice ◽  
Nmr Study

The proton NMR second moment and spin-lattice relaxation time have been studied for polycrystalline inclusion compounds of thiourea pyridinium chloride, bromide, iodide and their perdeuterated analogues in a wide temperature range. The pyridinium cation reorientation around the pseudohexagonal C6’ symmetry axis over inequivalent barriers and hindered rotation of the thiourea molecule around its C=S bond have been revealed. The activation parameters of the both motions have been found.

1H and 19F NMR Study of Cation and Anion Motions in Guanidinium Fluoroantimonates

1995 ◽  
Vol 50 (8) ◽  
pp. 742-748 ◽  
Author(s):  
M. Grottel ◽  
A. Kozak ◽  
Z. Pająk
Keyword(s):  
Solid Phase ◽  
Relaxation Times ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Fluorine Nmr ◽  
Spin Lattice ◽  
Nmr Study ◽  
Guanidinium Cation

Abstract Proton and fluorine NMR linewidths, second moments, and spin-lattice relaxation times of polycrystalline [C(NH2)3]2SbF5 and C(NH2)3SbF6 were studied in a wide temperature range. For the pentafluoroantimonate, C3-reorientation of the guanidinium cation and C4-reorientation of the SbF5 anion were revealed and their activation parameters determined. The dynamical inequivalence of the two guanidinium cations was evidenced. For the hexafluoroantimonate, two solid-solid phase transitions were found. In the low temperature phase the guanidinium cation undergoes C3 reorien­ tation while the SbF6 anion reorients isotropically. The respective activation parameters were derived. At high temperatures new ionic plastic phases were evidenced.

1H and 19 F NMR Study of Cation and Anion Motions in Guanidinium Hexafluorozirconate

1996 ◽  
Vol 51 (9) ◽  
pp. 991-996 ◽  
Author(s):  
M. Grottel ◽  
A. Kozak ◽  
Z. Pająk
Keyword(s):  
Solid Phase ◽  
Relaxation Times ◽  
High Mobility ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Fluorine Nmr ◽  
Spin Lattice ◽  
Nmr Study ◽  
Wide Range ◽  
Deuterated Analogue

Abstract Proton and fluorine NMR second moments and spin-lattice relaxation times of polycrystalline guanidinium hexafluorozirconate and its deuterated analogue were studied in laboratory (60 MHz) and rotating (H1 = 20 G) frames over a wide range of temperature. An analysis of the experimental results enabled us to reveal a dynamical inequivalence of two crystallographically independent cations and an unexpected high mobility of nonspherical anion dimers. A comparison of the ions dynamics in 2:1 complex studied with the guanidinium 1:1 and 3:1 complexes has shown a significant contribution of the hydrogen bonds to the potential barriers hindering the anion reorientations. At low temperatures a proton motion in the hydrogen bond and at 400 K a solid-solid phase transition have been discerned.

Proton NMR Study of Molecular Dynamics in Hydrazinium Perchlorate

1990 ◽  
Vol 45 (2) ◽  
pp. 102-106
Author(s):  
K. Ganesan ◽  
R. Damle ◽  
J. Ramakrishna
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Temperature Minimum ◽  
Second Moment ◽  
Spin Lattice ◽  
Nmr Study

AbstractThe proton spin-lattice relaxation time T1 (at 5.4, 10 and 15 MHz) and second moment M2 (at 9.8 MHz) have been measured in hydrazinium Perchlorate (N2H5ClO4). The temperature dependence of T, shows two minima. The low temperature T, minimum has been explained in terms of NH3 reorientation about the N-N axis while the high temperature minimum is attributed to the exchange of protons within the NH2 group (180° flip about the H - N - H bisectrix). The activation energies for NH3 and NH: motions are found to be 20.5 kJ mol-1 and 39.8 kJ mol-1 , respectively. The second moment variation with temperature shows two transitions around 120 K and 210 K and has been discussed in terms of NH3/NH2 motions.

Bis(pyridine)difluoroboron, tris(pyridine)fluoroboron, and other (pyridine)haloboron cations. A systematic NMR study

1996 ◽  
Vol 74 (7) ◽  
pp. 1309-1320 ◽  
Author(s):  
Melvin J. Farquharson ◽  
J. Stephen Hartman
Keyword(s):  
Key Words ◽  
Diagnostic Test ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Nmr Study

The adducts pyr•BF2Br and pyr•BFBr2 (pyr = pyridine) form fluoroboron cations by displacement of Br− by excess pyridine, the ease of cation formation being pyr2BF2+ » pyr2BFBr+ » pyr3BF2+•Cl− can be displaced from pyr•BF2Cl and pyr•BFCl2, but much less readily, to form pyr2BF2+, pyr2BFCl+, and, under forcing conditions, a few percent of pyr3BF2+. Non-fluorine-containing mixed boron trihalide adducts of pyridine also form haloboron cations by heaviest-halide-ion displacement, for example pyr•BClI2 giving pyr2BClI+, the ease of displacement always being I− > Br− > Cl−, and displacement always occurring more readily from mixed boron trihalide adducts than from unmixed-halogen adducts. The mechanistic implications of this are discussed. ortho Substituents greatly reduce the ability of pyridine to displace heavy halide ion, so 2-methylpyridine gives 2-Mepyr2BF2+ and 2-Mepyr2BFBr+ but not 2-Mepyr2BFCl+ or 2-Mepyr3BF2+, while 2,6-dimethylpyridine does not form any haloboron cations. 19F spin-lattice relaxation times of the fluoroboron cations are much shorter than those of neutral boron trihalide adducts in the same solution, and provide a further diagnostic test for their presence. Key words: fluoroboron cations, pyridines, mixed boron trihalide adducts, fluorine-19 NMR, boron-11 NMR.

A 2D deuterium NMR study of molecular reorientation in (CH3)3E+X- onium salts

2000 ◽  
Vol 78 (1) ◽  
pp. 46-50
Author(s):  
Andrew M Wachner ◽  
Kenneth R Jeffrey ◽  
Glenn H Penner
Keyword(s):  
Rotation Axis ◽  
General Structure ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Deuterium Nmr ◽  
Two Dimensional ◽  
Molecular Reorientation ◽  
Nmr Study ◽  
Onium Salts

Two dimensional deuterium NMR measurements are reported for three different onium salts (CH3)3SeNO3-d3, (CH3)3TeI-d3, and (CH3)3SI-d9. In these molecular solids with the general structure (CH3)3E+X-, three methyl groups are attached to the E atom. There is the possibility of reorientation of the methyls about their C3 axes and reorientation of the whole tri-methyl group about the C'3 axis. From an analysis of the 2D NMR exchange spectra the angle between the E-C bonds and the rotation axis for trimethyl reorientation were determined. Exchange rates and spin lattice relaxation times are given for several temperatures, to show how the mixing times for the experiments were selected. The data presented for (CH3)3TeI-d3, demonstrate that 2D techniques are sensitive to motions on a time scale an order of magnitude slower than that accessible using 1D line shape techniques.Key words: deuterium NMR, molecular motion, onium salts, two dimensional spectra.

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