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Osior A, Kalicki P, Kamieński B, Szymański S, Bernatowicz P, Shkurenko A. Nonclassical dynamics of the methyl group in 1,1,1-triphenylethane. Evidence from powder 1H NMR spectra. J Chem Phys 2017; 146:104504. [PMID: 28298104 DOI: 10.1063/1.4978226] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
According to the damped quantum rotation (DQR) theory, hindered rotation of methyl groups, evidenced in nuclear magnetic resonance (NMR) line shapes, is a nonclassical process. It comprises a number of quantum-rate processes measured by two different quantum-rate constants. The classical jump model employing only one rate constant is reproduced if these quantum constants happen to be equal. The values of their ratio, or the nonclassicallity coefficient, determined hitherto from NMR spectra of single crystals and solutions range from about 1.20 to 1.30 in the latter case to above 5.0 in the former, with the value of 1 corresponding to the jump model. Presently, first systematic investigations of the DQR effects in wide-line NMR spectra of a powder sample are reported. For 1,1,1-triphenylethane deuterated in the aromatic positions, the relevant line-shape effects were monitored in the range 99-121 K. The values of the nonclassicality coefficient dropping from 2.7 to 1.7 were evaluated in line shape fits to the experimental powder spectra from the range 99-108 K. At these temperatures, the fits with the conventional line-shape model are visibly inferior to the DQR fits. Using a theoretical model reported earlier, a semiquantitative interpretation of the DQR parameters evaluated from the spectra is given. It is shown that the DQR effects as such can be detected in wide-line NMR spectra of powdered samples, which are relatively facile to measure. However, a fully quantitative picture of these effects can only be obtained from the much more demanding experiments on single crystals.
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Affiliation(s)
- Agnieszka Osior
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland
| | - Przemysław Kalicki
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland
| | - Bohdan Kamieński
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland
| | - Sławomir Szymański
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland
| | - Piotr Bernatowicz
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland
| | - Aleksander Shkurenko
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland
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Bernatowicz P, Shkurenko A, Osior A, Kamieński B, Szymański S. A quantum mechanical alternative to the Arrhenius equation in the interpretation of proton spin-lattice relaxation data for the methyl groups in solids. Phys Chem Chem Phys 2015; 17:28866-78. [PMID: 26451661 DOI: 10.1039/c5cp04924e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The theory of nuclear spin-lattice relaxation in methyl groups in solids has been a recurring problem in nuclear magnetic resonance (NMR) spectroscopy. The current view is that, except for extreme cases of low torsional barriers where special quantum effects are at stake, the relaxation behaviour of the nuclear spins in methyl groups is controlled by thermally activated classical jumps of the methyl group between its three orientations. The temperature effects on the relaxation rates can be modelled by Arrhenius behaviour of the correlation time of the jump process. The entire variety of relaxation effects in protonated methyl groups have recently been given a consistent quantum mechanical explanation not invoking the jump model regardless of the temperature range. It exploits the damped quantum rotation (DQR) theory originally developed to describe NMR line shape effects for hindered methyl groups. In the DQR model, the incoherent dynamics of the methyl group include two quantum rate (i.e., coherence-damping) processes. For proton relaxation only one of these processes is relevant. In this paper, temperature-dependent proton spin-lattice relaxation data for the methyl groups in polycrystalline methyltriphenyl silane and methyltriphenyl germanium, both deuterated in aromatic positions, are reported and interpreted in terms of the DQR model. A comparison with the conventional approach exploiting the phenomenological Arrhenius equation is made. The present observations provide further indications that incoherent motions of molecular moieties in the condensed phase can retain quantum character over much broader temperature range than is commonly thought.
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Affiliation(s)
- Piotr Bernatowicz
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
| | - Aleksander Shkurenko
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland. and Functional Materials Design, Discovery and Development Research Group (FMD3), Advanced Membranes and Porous Materials Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Agnieszka Osior
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
| | - Bohdan Kamieński
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
| | - Sławomir Szymański
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
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3
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Szymański S. Spin-lattice relaxation of the methyl group protons in solids revisited: damped quantum rotation approach. J Chem Phys 2012; 137:034513. [PMID: 22830717 DOI: 10.1063/1.4734251] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Proton spin-lattice relaxation of the methyl group in solids had been one of the most thoroughly addressed theoretical problems in nuclear magnetic resonance (NMR) spectroscopy, considered at different levels of sophistication. For systems with substantial quantum tunneling effects, several quantum mechanical treatments were reported, although in practical applications the quantum models were always augmented with or replaced by the classical jump model. However, the latter has recently proved invalid in the description of NMR line shape effects in variable-temperature spectra of hindered methyl groups, while the competing theory of damped quantum rotation (DQR) was shown to be adequate. In this work, the spin-lattice relaxation issue for the methyl protons is readdressed using the latter theory. The main outcome is that, while the existing formulas for the relaxation rates remain unchanged, the crucial parameter entering them, the correlation time of the relevant random process, need to be reinterpreted. It proves to be the inverse of one of the two quantum-rate constants entering the DQR model, neither of which, when taken separately, can be related to the jump process. It can be identified with one describing the life-time broadening of the tunnel peaks in inelastic neutron scattering (INS) spectra of the methyl groups. Such a relationship between the relaxation and INS effects was reported from another laboratory long ago, but only for the low-temperature limit where thermal population of the excited torsional levels of the methyl group can be neglected. The whole spectrum of cases encountered in practical relaxation studies on protonated methyl groups is addressed for the first time. Preliminary experimental confirmation of this novel approach is reported, based on already published NMR data for a single crystal of methylmalonic acid. The once extensively debated issues of quenching of the coherent tunneling and of the classical limit in the dynamics of the methyl groups are readdressed and presented in a consistent manner.
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Affiliation(s)
- S Szymański
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland.
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Došlić N, Gomzi V, Mališ M, Matanović I, Eckert J. Fluxionality of Hydrogen Ligands in Fe(H)2(H2)(PEtPh2)3. Inorg Chem 2011; 50:10740-7. [DOI: 10.1021/ic201248z] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Nađa Došlić
- Department of Physical Chemistry, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Vjeran Gomzi
- Department of Physical Chemistry, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Momir Mališ
- Department of Physical Chemistry, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Ivana Matanović
- Department of Physical Chemistry, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Juergen Eckert
- Materials Research Laboratory, University of California, Santa Barbara, California 93106, United States
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Szymański S. Theory of damped quantum rotation in nuclear magnetic resonance spectra. III. Nuclear permutation symmetry of the line shape equation. J Chem Phys 2009; 131:244504. [PMID: 20059076 DOI: 10.1063/1.3276452] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The damped quantum rotation (DQR) theory describes manifestations in nuclear magnetic resonance spectra of the coherent and stochastic dynamics of N-fold molecular rotors composed of indistinguishable particles. The standard jump model is only a limiting case of the DQR approach; outside this limit, the stochastic motions of such rotors have no kinematic description. In this paper, completing the previous two of this series, consequences of nuclear permutation symmetry for the properties of the DQR line shape equation are considered. The systems addressed are planar rotors, such as aromatic hydrocarbons' rings, occurring inside of molecular crystals oriented in the magnetic field. Under such conditions, oddfold rotors can have nontrivial permutation symmetries only for peculiar orientations while evenfold ones always retain their intrinsic symmetry element, which is rotation by 180 degrees about the N-fold axis; in specific orientations the latter can gain two additional symmetry elements. It is shown that the symmetry selection rules applicable to the classical rate processes in fluids, once recognized as having two diverse aspects, macroscopic and microscopic, are also rigorously valid for the DQR processes in the solid state. However, formal justification of these rules is different because the DQR equation is based on the Pauli principle, which is ignored in the jump model. For objects like the benzene ring, exploitation of these rules in simulations of spectra using the DQR equation can be of critical significance for the feasibility of the calculations. Examples of such calculations for the proton system of the benzene ring in a general orientation are provided. It is also shown that, because of the intrinsic symmetries of the evenfold rotors, many of the DQR processes, which such rotors can undergo, are unobservable in NMR spectra.
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Affiliation(s)
- S Szymański
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warszawa, Poland.
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Piślewski N, Tritt-Goc J, Bielejewski M, Rachocki A, Ratajczyk T, Szymański S. Spin-lattice relaxation study of the methyl proton dynamics in solid 9,10-dimethyltriptycene (DMT). SOLID STATE NUCLEAR MAGNETIC RESONANCE 2009; 35:194-200. [PMID: 19181490 DOI: 10.1016/j.ssnmr.2008.12.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2008] [Revised: 11/25/2008] [Accepted: 12/11/2008] [Indexed: 05/27/2023]
Abstract
Proton spin-lattice relaxation studies are performed for powder samples of 9,10-dimethyltriptycene (DMT) and its isotopomer DMT-d(12) in which all the non-methyl protons in the molecule are replaced by deuterons. The relaxation data are interpreted in terms of the conventional relaxation theory based on the random jump model in which the Pauli correlations between the relevant spin and torsional states are discarded. The Arrhenius activation energies, obtained from the relaxation data, 25.3 and 24.8 kJ mol(-1) for DMT and DMT-d(12), respectively, are very high as for the methyl groups. The validity of the jump model in the present case is considered from the perspective of Haupt theory in which the Pauli principle is explicitly invoked. To this purpose, the dynamic quantities entering the Haupt model are reinterpreted in the spirit of the damped quantum rotation (DQR) approach introduced recently for the purpose of NMR lineshape studies of hindered molecular rotators. Theoretical modelling of the relevant methyl group dynamics, based on the DQR theory, was performed. From these calculations it is inferred that direct assessments of the torsional barrier heights, based on the Arrhenius activation energies extracted from relaxation data, should be treated with caution.
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Affiliation(s)
- N Piślewski
- Institute of Molecular Physics, Polish Academy of Sciences, Poznań, Poland.
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7
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Sobczyk L, Prager M, Sawka-Dobrowolska W, Bator G, Pawlukojć A, Grech E, van Eijck L, Ivanov A, Rols S, Wuttke J, Unruh T. The structure of diaminodurene and the dynamics of the methyl groups. J Chem Phys 2009; 130:164519. [DOI: 10.1063/1.3125629] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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8
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Ratajczyk T, Szymański S. Theory of damped quantum rotation in nuclear magnetic resonance spectra. II. Numerical simulations for the benzene rotor. J Chem Phys 2007; 127:184504. [DOI: 10.1063/1.2785180] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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9
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McDonald P, Vijayaraghavan D, Debenham P, Horsewill A. Pressure dependence of methyl tunnelling in solid diacetyl. Mol Phys 2006. [DOI: 10.1080/00268979300100181] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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10
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Gutsche P, Schmitt H, Haeberlen U, Ratajczyk T, Szymanski S. Fingerprints of Damped Quantum Rotation Observed in Solid-State Proton NMR Spectra. Chemphyschem 2006; 7:886-93. [PMID: 16596612 DOI: 10.1002/cphc.200500572] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
(1)H NMR spectra of the methyl group in an oriented crystal sample of methylmalonic acid with all three non-methyl protons replaced by deuterons are interpreted in terms of the damped quantum rotation (DQR) theory of NMR line shapes. The DQR approach offers a perfect theoretical reproduction of the observed spectra while the conventional Alexander-Binsch line-shape model shows evident defects in the present case. The temperature trends of the quantities characterizing the coherent and incoherent dynamics of the methyl group in the DQR approach (the effective tunnelling frequency and two coherence-damping rates) derived from the spectra are fairly reproduced using a model reported previously. The present findings provide further evidence of limitations to the validity of the common belief that molecular rate processes in condensed phases are necessarily classical.
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Affiliation(s)
- Peter Gutsche
- Max-Planck Institute for Medical Research, 69120 Heidelberg, Germany
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11
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Colmenero J, Moreno AJ, Alegría A. Neutron scattering investigations on methyl group dynamics in polymers. Prog Polym Sci 2005. [DOI: 10.1016/j.progpolymsci.2005.08.001] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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12
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Ratajczyk T, Szymański S. Theory of damped quantum rotation in NMR spectra. I. Fundamental aspects. J Chem Phys 2005; 123:204509. [PMID: 16351283 DOI: 10.1063/1.2131868] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The damped quantum rotation (DQR) theory, formulated originally for methyl-like atomic groupings, is now extended to hindered (N>3)-fold molecular rotors, such as the cyclopentadienyl, benzene, and cycloheptatrienyl rings in solid phase environments. It heightens the significance of the Pauli principle in shaping up the stochastic dynamics of such objects, reflected in NMR line shapes. The corresponding NMR line-shape equation is derived; its stochastic part is shown for the first time to have the double commutator form for any values of the quantum-mechanical (coherence-damping) rate constants entering it. Constraints on the relative magnitudes of such constants are determined under which the DQR line-shape equation is converted into the phenomenological Alexander-Binsch equation describing classical jumps of the rotor. When all the quantum rate constants happen to be equal, the phenomenological model of equal jump rates between any two of the N (equivalent) orientations of the rotor is reproduced. On the other hand, the seemingly most plausible (for N>3) nearest-neighbor hopping model does not have any peculiar grounds in the DQR approach. For the special instances of stochastic molecular motions addressed in this work, the extended DQR formalism affords a quantification of the "degree of classicality" represented by a complete set of the relevant quantum rate constants. In view of our earlier experimental findings for the methyl rotors, the very occurrence of the nonclassical DQR effects seems unquestionable even for the objects of the size of benzene. The question of under what circumstances such effects can be big enough to be detected experimentally will be addressed in Part II of this work.
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Affiliation(s)
- T Ratajczyk
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44, 01-224 Warszawa, Poland
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13
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Birczyński A, Lalowicz Z, Łodziana Z. Rotational barriers in ammonium hexachlorometallates as studied by NMR, tunnelling spectroscopy and ab initio calculations. Chem Phys 2004. [DOI: 10.1016/j.chemphys.2003.12.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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14
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Bernatowicz P, Szymański S. NMR lineshape equations for hindered methyl group: a comparison of the semi-classical and quantum mechanical models. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2003; 164:60-64. [PMID: 12932456 DOI: 10.1016/s1090-7807(03)00185-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The semiclassical and quantum mechanical NMR lineshape equations for a hindered methyl group are compared. In both the approaches, the stochastic dynamics can be interpreted in terms of a progressive symmetrization of the spin density matrix. However, the respective ways of achieving the same limiting symmetry can be remarkably different. From numerical lineshape simulations it is inferred that in the regime of intermediate exchange, where the conventional theory predicts occurrence of a single Lorentzian, the actual spectrum can have nontrivial features. This observation may open new perspectives in the search for nonclassical effects in the stochastic behavior of methyl groups in liquid-phase NMR.
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Affiliation(s)
- P Bernatowicz
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland
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15
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Prager M, Schiebel P, Grimm H. Rotational tunneling of NH4 and NH3D and dipolar interaction in (NH3.6D0.4)2PtCl6. J Chem Phys 2002. [DOI: 10.1063/1.1477185] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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16
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Würger A. Resonant coupling of free quantum rotors in inclusion compounds. PHYSICAL REVIEW LETTERS 2002; 88:063002. [PMID: 11863803 DOI: 10.1103/physrevlett.88.063002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2001] [Indexed: 05/23/2023]
Abstract
NH3 groups in certain Hofmann clathrates form almost free one-dimensional quantum rotors with energy levels E(n) = n(2)B and angular momentum n (planck constant), where n = 0, +/-1, +/-2,.... Recent neutron scattering experiments revealed a surprising temperature dependence for the linewidths of the n = 0 <--> 1, 0 <--> 2, and 1 <--> 2 transitions. We propose a novel line broadening mechanism based on rotor-rotor coupling and obtain a simple analytic expression for the widths that depends on the rotor level occupation and on the 3-proton spin degeneracies of initial and final states. Our model provides, without adjustable parameters, a good fit both to the temperature dependence of the observed widths and to their relative magnitude.
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Affiliation(s)
- Alois Würger
- Université Bordeaux 1, CPMOH, 351 cours de la Libération, 33405 Talence, France
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17
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Moreno AJ, Alegría A, Colmenero J, Frick B. Methyl Group Dynamics in Poly(methyl methacrylate): From Quantum Tunneling to Classical Hopping. Macromolecules 2001. [DOI: 10.1021/ma0100854] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- A. J. Moreno
- Departamento de Física de Materiales y Centro Mixto CSIC-UPV/EHU, Universidad del País Vasco (UPV/EHU), Apartado 1072, 20080 San Sebastián, Spain
| | - A. Alegría
- Departamento de Física de Materiales y Centro Mixto CSIC-UPV/EHU, Universidad del País Vasco (UPV/EHU), Apartado 1072, 20080 San Sebastián, Spain
| | - J. Colmenero
- Departamento de Física de Materiales y Centro Mixto CSIC-UPV/EHU, Universidad del País Vasco (UPV/EHU), Apartado 1072, 20080 San Sebastián, Spain
| | - B. Frick
- Institute Laue Langevin, BP 156X, F-38042 Grenoble, France
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Szymański S, Olejniczak Z, Detken A, Haeberlen U. Iterative lineshape analysis of quadrupolar echo spectra of a damped CD(3) quantum rotor: preliminary evidence of a novel mechanism of stochastic spin exchange. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2001; 148:277-288. [PMID: 11237633 DOI: 10.1006/jmre.2000.2252] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
It is demonstrated that the wealth of information about damped quantum rotation of CD(3) groups, contained in quadrupolar echo spectra, can be fully explored in a broad temperature range using a method of iterative analysis of the spectral lineshapes. The recently reported lineshape equation which, apart from the quantum tunneling and the dissipative Alexander--Binsch terms, contains an additional dissipative term having no classical analog is shown to be capable of describing even subtle details of the spectra of a crystal of acetylsalicylic acid--CD(3) oriented specifically in the magnetic field. Preliminary evidence of the occurrence of this novel dissipative mechanism in the system studied is reported. The results obtained seem to suggest that there is no "classical limit" in the dissipative behavior of this system.
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Affiliation(s)
- S Szymański
- Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
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20
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Clough S, McDonald PJ, Zelaya FO. The transition from free quantum tunnelling to thermally driven motion of methyl groups. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/17/25/005] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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21
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22
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Szymański S. Nuclear magnetic resonance line shapes of methyl-like quantum rotors in low-temperature solids. J Chem Phys 1999. [DOI: 10.1063/1.479289] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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23
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Rodriguez V, Sabo-Etienne S, Chaudret B, Thoburn J, Ulrich S, Limbach HH, Eckert J, Barthelat JC, Hussein K, Marsden CJ. Fluxionality and Isomerism of the Bis(dihydrogen) Complex RuH(2)(H(2))(2)(PCy(3))(2): INS, NMR, and Theoretical Studies. Inorg Chem 1998; 37:3475-3485. [PMID: 11670430 DOI: 10.1021/ic970697y] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To study the fluxionality of the bis(dihydrogen) complex RuH(2)(H(2))(2)(PCy(3))(2) (1), NMR spectra were recorded in Freons (mixture of CDCl(3), CDFCl(2), and CDF(2)Cl). 1 was found to remain fluxional at all temperatures, but the presence of CDCl(3) necessary for its solubilization induces its transformation into, first, RuHCl(H(2))(2)(PCy(3))(2) (3) and the new ruthenium(IV) dihydride RuH(2)Cl(2)(PCy(3))(2) (4). 4 is produced selectively in pure CDCl(3) but reacts further to give a mixture of chloro complexes. 4 was isolated from the reaction of 1 with aqueous HCl in Et(2)O and shows a fluxional process attributed to the interconversion between two symmetrical isomers. The activation parameters of this process were obtained by (1)H NMR line shape analysis, as well as those corresponding to the exchange between 3 and free dihydrogen. The fluxionality of the dihydrogen-hydride system is also evident at a much faster time scale than that of NMR studies in the inelastic neutron scattering observations of the rotation of the dihydrogen ligands. The geometries and relative energies of several isomers of complexes 1, 3, and 4 were studied using density functional theory (DFT) and MP2 methods, together with a few coupled-cluster (CCSD(T)) calculations. In contrast to what might have been expected, the two hydrides and the two H(2) units of 1 lie in the same plane, due to the attractive "cis effect" created by the hydrides. The two H(2) ligands adopt cis positions in the lowest-energy isomer. Rotation of the two dihydrogen ligands has been analyzed using DFT calculations. A slight preference for a C(2) conrotatory pathway has been found with a calculated barrier in good agreement with the experimental INS value. Two low-energy isomers of 4 have been characterized computationally, both of which have C(2)(v)() symmetry, consistent with the solution NMR spectra.
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Affiliation(s)
- Venancio Rodriguez
- Laboratoire de Physique Quantique, UMR IRSAMC-CNRS UMR 5626, Université Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse Cedex 4, France
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Cleemput MV, Buekenhoudt A, Gerven LV, Horsewill AJ. Quantum and classical dynamics of a methyl group with tunneling frequency 3.4 MHz studied by low field NMR. J Chem Phys 1995. [DOI: 10.1063/1.470515] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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25
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Prager M, Monkenbusch M, Ibberson RM, David WIF, Cavagnat D. Methyl rotational potentials and transferable pair potentials in toluene. J Chem Phys 1993. [DOI: 10.1063/1.464914] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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26
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van der Putten D, Diezemann G, Fujara F, Hartmann K, Sillescu H. Methyl group dynamics in α‐crystallized toluene as studied by deuteron spin–lattice relaxation. J Chem Phys 1992. [DOI: 10.1063/1.462130] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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27
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Symmetry breaking in thermally activated NH4 rotation studied by NMR level crossing spectroscopy. Chem Phys 1991. [DOI: 10.1016/0301-0104(91)85009-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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