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Kveder M, Rakvin B, You J. A quantum many body model for the embedded electron spin decoherence in organic solids. J Chem Phys 2019; 151:164124. [DOI: 10.1063/1.5124561] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Marina Kveder
- Division of Physical Chemistry, Ruder Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Boris Rakvin
- Division of Physical Chemistry, Ruder Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
| | - Jiangyang You
- Division of Physical Chemistry, Ruder Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
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2
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Beckmann PA, Ford J, Malachowski WP, McGhie AR, Moore CE, Rheingold AL, Sloan GJ, Szewczyk ST. Proton Spin-Lattice Relaxation in Organic Molecular Solids: Polymorphism and the Dependence on Sample Preparation. Chemphyschem 2018; 19:2423-2436. [PMID: 29956438 DOI: 10.1002/cphc.201800237] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2018] [Indexed: 11/07/2022]
Abstract
We report solid-state nuclear magnetic resonance 1 H spin-lattice relaxation, single-crystal X-ray diffraction, powder X-ray diffraction, field emission scanning electron microscopy, and differential scanning calorimetry in solid samples of 2-ethylanthracene (EA) and 2-ethylanthraquinone (EAQ) that have been physically purified in different ways from the same commercial starting compounds. The solid-state 1 H spin-lattice relaxation is always non-exponential at high temperatures as expected when CH3 rotation is responsible for the relaxation. The 1 H spin-lattice relaxation experiments are very sensitive to the "several-molecule" (clusters) structure of these van der Waals molecular solids. In the three differently prepared samples of EAQ, the relaxation also becomes very non-exponential at low temperatures. This is very unusual and the decay of the nuclear magnetization can be fitted with both a stretched exponential and a double exponential. This unusual result correlates with the powder X-ray diffractometry results and suggests that the anomalous relaxation is due to crystallites of two (or more) different polymorphs (concomitant polymorphism).
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Affiliation(s)
- Peter A Beckmann
- Department of Physics, Bryn Mawr College, Bryn Mawr, Pennsylvania, USA
| | - Jamie Ford
- Nanoscale Characterization Facility Singh Center for Nanotechnology, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | | | - Andrew R McGhie
- Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Curtis E Moore
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, USA
| | - Arnold L Rheingold
- Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California, USA
| | - Gilbert J Sloan
- Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Steven T Szewczyk
- Department of Materials Science and Engineering School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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Meier T, Petitgirard S, Khandarkhaeva S, Dubrovinsky L. Observation of nuclear quantum effects and hydrogen bond symmetrisation in high pressure ice. Nat Commun 2018; 9:2766. [PMID: 30018359 PMCID: PMC6050302 DOI: 10.1038/s41467-018-05164-x] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Accepted: 06/15/2018] [Indexed: 11/19/2022] Open
Abstract
Hydrogen bond symmetrisations in H-bonded systems triggered by pressure-induced nuclear quantum effects (NQEs) is a long-known concept but experimental evidence in high-pressure ices has remained elusive with conventional methods. Theoretical works predicted quantum-mechanical tunneling of protons within water ices to occur at pressures above 30 GPa, and the H-bond symmetrisation transition to occur above 60 GPa. Here we used 1H-NMR on high-pressure ice up to 97 GPa, and demonstrate that NQEs govern the behavior of the hydrogen bonded protons in ice VII already at significantly lower pressures than previously expected. A pronounced tunneling mode was found to be present up to the highest pressures of 97 GPa, well into the stability field of ice X, where NQEs are not anticipated in a fully symmetrised H-bond network. We found two distinct transitions in the NMR shift data at about 20 GPa and 75 GPa attributed to the step-wise symmetrisation of the H-bond.
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Affiliation(s)
- Thomas Meier
- Bayerisches Geoinstitut, Bayreuth University, Universitätsstraße 30, 95447, Bayreuth, Germany.
| | - Sylvain Petitgirard
- Bayerisches Geoinstitut, Bayreuth University, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Saiana Khandarkhaeva
- Bayerisches Geoinstitut, Bayreuth University, Universitätsstraße 30, 95447, Bayreuth, Germany
| | - Leonid Dubrovinsky
- Bayerisches Geoinstitut, Bayreuth University, Universitätsstraße 30, 95447, Bayreuth, Germany
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Beckmann PA, Bohen JM, Ford J, Malachowski WP, Mallory CW, Mallory FB, McGhie AR, Rheingold AL, Sloan GJ, Szewczyk ST, Wang X, Wheeler KA. Monitoring a simple hydrolysis process in an organic solid by observing methyl group rotation. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2017; 85-86:1-11. [PMID: 28260612 DOI: 10.1016/j.ssnmr.2017.01.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Revised: 12/26/2016] [Accepted: 01/24/2017] [Indexed: 06/06/2023]
Abstract
We report a variety of experiments and calculations and their interpretations regarding methyl group (CH3) rotation in samples of pure 3-methylglutaric anhydride (1), pure 3-methylglutaric acid (2), and samples where the anhydride is slowly absorbing water from the air and converting to the acid [C6H8O3(1) + H2O → C6H10O4(2)]. The techniques are solid state 1H nuclear magnetic resonance (NMR) spin-lattice relaxation, single-crystal X-ray diffraction, electronic structure calculations in both isolated molecules and in clusters of molecules that mimic the crystal structure, field emission scanning electron microscopy, differential scanning calorimetry, and high resolution 1H NMR spectroscopy. The solid state 1H spin-lattice relaxation experiments allow us to observe the temperature dependence of the parameters that characterize methyl group rotation in both compounds and in mixtures of the two compounds. In the mixtures, both types of methyl groups (that is, molecules of 1 and 2) can be observed independently and simultaneously at low temperatures because the solid state 1H spin-lattice relaxation is appropriately described by a double exponential. We have followed the conversion 1 → 2 over periods of two years. The solid state 1H spin-lattice relaxation experiments in pure samples of 1 and 2 indicate that there is a distribution of NMR activation energies for methyl group rotation in 1 but not in 2 and we are able to explain this in terms of the particle sizes seen in the field emission scanning electron microscopy images.
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Affiliation(s)
- Peter A Beckmann
- Department of Physics, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, PA 19010-2899, USA.
| | - Joseph M Bohen
- Department of Chemistry, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, PA 19010-2899, USA
| | - Jamie Ford
- Nanoscale Characterization Facility, Singh Center for Nanotechnology, University of Pennsylvania, 3205 Walnut St., Philadelphia, PA 19104-3405, USA
| | - William P Malachowski
- Department of Chemistry, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, PA 19010-2899, USA
| | - Clelia W Mallory
- Department of Chemistry, University of Pennsylvania, 231 South 34 Street, Philadelphia, PA 19104-6323, USA
| | - Frank B Mallory
- Department of Chemistry, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, PA 19010-2899, USA
| | - Andrew R McGhie
- Laboratory for Research on the Structure of Matter, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6202, USA
| | - Arnold L Rheingold
- Department of Chemistry and Biochemistry, University of California, San Diego, 5128 Urey Hall, 9500 Gilman Dr., La Jolla, CA 92093-0358, USA
| | - Gilbert J Sloan
- Laboratory for Research on the Structure of Matter, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6202, USA
| | - Steven T Szewczyk
- Department of Materials Science and Engineering, School of Engineering and Applied Science, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6202, USA
| | - Xianlong Wang
- Key Laboratory for NeuroInformation of Ministry of Education, School of Life Science and Technology, University of Electronic Science and Technology of China, 4 North Jianshe Rd., 22nd Section, Chengdu 610054, China
| | - Kraig A Wheeler
- Department of Chemistry, Eastern Illinois University, 600 Lincoln Ave., Charleston, IL 69120-3099, USA
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Beckmann PA, McGhie AR, Rheingold AL, Sloan GJ, Szewczyk ST. Solid-Solid Phase Transitions and tert-Butyl and Methyl Group Rotation in an Organic Solid: X-ray Diffractometry, Differential Scanning Calorimetry, and Solid-State 1H Nuclear Spin Relaxation. J Phys Chem A 2017; 121:6220-6230. [PMID: 28742961 DOI: 10.1021/acs.jpca.7b06265] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Using solid-state 1H nuclear magnetic resonance (NMR) spin-lattice relaxation experiments, we have investigated the effects of several solid-solid phase transitions on tert-butyl and methyl group rotation in solid 1,3,5-tri-tert-butylbenzene. The goal is to relate the dynamics of the tert-butyl groups and their constituent methyl groups to properties of the solid determined using single-crystal X-ray diffraction and differential scanning calorimetry (DSC). On cooling, the DSC experiments see a first-order, solid-solid phase transition at either 268 or 155 K (but not both) depending on thermal history. The 155 K transition (on cooling) is identified by single-crystal X-ray diffraction to be one from a monoclinic phase (above 155 K), where the tert-butyl groups are disordered (that is, with a rotational 6-fold intermolecular potential dominating), to a triclinic phase (below 155 K), where the tert-butyl groups are ordered (that is, with a rotational 3-fold intermolecular potential dominating). This transition shows very different DSC scans when both a 4.7 mg polycrystalline sample and a 19 mg powder sample are used. The 1H spin-lattice relaxation experiments with a much larger 0.7 g sample are very complicated and, depending on thermal history, can show hysteresis effects over many hours and over very large temperature ranges. In the high-temperature monoclinic phase, the tert-butyl groups rotate with NMR activation energies (closely related to rotational barriers) in the 17-23 kJ mol-1 range, and the constituent methyl groups rotate with NMR activation energies in the 7-12 kJ mol-1 range. In the low-temperature triclinic phase, the rotations of the tert-butyl groups and their methyl groups in the aromatic plane are quenched (on the NMR time scale). The two out-of-plane methyl groups in the tert-butyl groups are rotating with activation energies in the 5-11 kJ mol-1 range.
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Affiliation(s)
- Peter A Beckmann
- Department of Physics, Bryn Mawr College , 101 North Merion Avenue, Bryn Mawr, Pennsylvania 19010-2899, United States
| | | | - Arnold L Rheingold
- Department of Chemistry and Biochemistry, University of California, San Diago , 5128 Urey Hall, 9500 Gilman Drive, La Jolla, California 92093-0358, United States
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Beckmann PA, Rheingold AL. 1H and 19F spin-lattice relaxation and CH3 or CF3 reorientation in molecular solids containing both H and F atoms. J Chem Phys 2016; 144:154308. [DOI: 10.1063/1.4944981] [Citation(s) in RCA: 6] [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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7
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Beckmann PA, Moore CE, Rheingold AL. Methyl and t-butyl group rotation in a molecular solid: 1H NMR spin-lattice relaxation and X-ray diffraction. Phys Chem Chem Phys 2016; 18:1720-6. [DOI: 10.1039/c5cp04994f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We report solid state 1H nuclear magnetic resonance spin-lattice relaxation experiments and X-ray diffractometry in 2-t-butyldimethylsilyloxy-6-bromonaphthalene.
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Affiliation(s)
| | - Curtis E. Moore
- Department of Chemistry and Biochemistry
- University of California
- La Jolla
- USA
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8
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Beckmann PA. Nonexponential (1)H spin-lattice relaxation and methyl group rotation in molecular solids. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2015; 71:91-95. [PMID: 26256302 DOI: 10.1016/j.ssnmr.2015.07.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 07/14/2015] [Indexed: 06/04/2023]
Abstract
We report a quantitative measure of the nonexponential (1)H spin-lattice relaxation resulting from methyl group (CH3) rotation in six polycrystalline van der Waals solids. We briefly review the subject in general to put the report in context. We then summarize several significant issues to consider when reporting (1)H or (19)F spin-lattice relaxation measurements when the relaxation is resulting from the rotation of a CH3 or CF3 group in a molecular solid.
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Affiliation(s)
- Peter A Beckmann
- Department of Physics, Bryn Mawr College, Bryn Mawr, PA 19010, USA.
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9
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Wang X, Mallory FB, Mallory CW, Odhner HR, Beckmann PA. Solid state ¹H spin-lattice relaxation and isolated-molecule and cluster electronic structure calculations in organic molecular solids: the relationship between structure and methyl group and t-butyl group rotation. J Chem Phys 2014; 140:194304. [PMID: 24852535 DOI: 10.1063/1.4874157] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We report ab initio density functional theory electronic structure calculations of rotational barriers for t-butyl groups and their constituent methyl groups both in the isolated molecules and in central molecules in clusters built from the X-ray structure in four t-butyl aromatic compounds. The X-ray structures have been reported previously. We also report and interpret the temperature dependence of the solid state (1)H nuclear magnetic resonance spin-lattice relaxation rate at 8.50, 22.5, and 53.0 MHz in one of the four compounds. Such experiments for the other three have been reported previously. We compare the computed barriers for methyl group and t-butyl group rotation in a central target molecule in the cluster with the activation energies determined from fitting the (1)H NMR spin-lattice relaxation data. We formulate a dynamical model for the superposition of t-butyl group rotation and the rotation of the t-butyl group's constituent methyl groups. The four compounds are 2,7-di-t-butylpyrene, 1,4-di-t-butylbenzene, 2,6-di-t-butylnaphthalene, and 3-t-butylchrysene. We comment on the unusual ground state orientation of the t-butyl groups in the crystal of the pyrene and we comment on the unusually high rotational barrier of these t-butyl groups.
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Affiliation(s)
- Xianlong Wang
- Key Laboratory for NeuroInformation of Ministry of Education, School of Life Science and Technology, University of Electronic Science and Technology of China, 4 North Jianshe Rd., 2nd Section, Chengdu 610054, China
| | - Frank B Mallory
- Department of Chemistry, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, Pennsylvania 19010-2899, USA
| | - Clelia W Mallory
- Department of Chemistry, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, Pennsylvania 19010-2899, USA
| | - Hosanna R Odhner
- Department of Physics, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, Pennsylvania 19010-2899, USA
| | - Peter A Beckmann
- Department of Physics, Bryn Mawr College, 101 North Merion Ave., Bryn Mawr, Pennsylvania 19010-2899, USA
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Martínez JI, Alonso PJ, García-Rubio I, Medina M. Methyl rotors in flavoproteins. Phys Chem Chem Phys 2014; 16:26203-12. [DOI: 10.1039/c4cp03115f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
ENDOR evidence shows that methyl groups in flavin behave as quantum locked rotors.
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Affiliation(s)
- Jesús I. Martínez
- Instituto de Ciencia de Materiales de Aragón
- Universidad de Zaragoza-Consejo Superior de Investigaciones Científicas
- Facultad de Ciencias
- 50009 Zaragoza, Spain
| | - Pablo J. Alonso
- Instituto de Ciencia de Materiales de Aragón
- Universidad de Zaragoza-Consejo Superior de Investigaciones Científicas
- Facultad de Ciencias
- 50009 Zaragoza, Spain
| | - Inés García-Rubio
- Laboratory of Physical Chemistry
- ETH Zurich
- 8093 Zürich, Switzerland
- Centro Universitario de la Defensa
- 50090 Zaragoza, Spain
| | - Milagros Medina
- Departamento de Bioquímica y Biología Molecular y Celular and Instituto de Biocomputación y Física de Sistemas Complejos (BIFI)
- Universidad de Zaragoza
- 50009 Zaragoza, Spain
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11
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Beckmann PA, Conn KG, Mallory CW, Mallory FB, Rheingold AL, Rotkina L, Wang X. Distributions of methyl group rotational barriers in polycrystalline organic solids. J Chem Phys 2013; 139:204501. [DOI: 10.1063/1.4830411] [Citation(s) in RCA: 11] [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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12
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Fahey DP, Dougherty WG, Kassel WS, Wang X, Beckmann PA. Nonexponential Solid State 1H and 19F Spin–Lattice Relaxation, Single-crystal X-ray Diffraction, and Isolated-Molecule and Cluster Electronic Structure Calculations in an Organic Solid: Coupled Methyl Group Rotation and Methoxy Group Libration in 4,4′-Dimethoxyoctafluorobiphenyl. J Phys Chem A 2012; 116:11946-56. [DOI: 10.1021/jp3075892] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Donald P. Fahey
- Department of Physics, Bryn Mawr College, 101 North Merion Avenue, Bryn Mawr,
Pennsylvania 19010-2899, United States
| | - William G. Dougherty
- Department of Chemistry, Villanova University, 800 Lancaster Avenue, Villanova,
Pennsylvania 19085-1597, United States
| | - W. Scott Kassel
- Department of Chemistry, Villanova University, 800 Lancaster Avenue, Villanova,
Pennsylvania 19085-1597, United States
| | - Xianlong Wang
- School of Life Science and Technology, University of Electronic Science and Technology of China, 4 North Jianshe Road, Second Section, Chengdu, China 610054
| | - Peter A. Beckmann
- Department of Physics, Bryn Mawr College, 101 North Merion Avenue, Bryn Mawr,
Pennsylvania 19010-2899, United States
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Beckmann PA, Schneider E. Methyl group rotation,1H spin-lattice relaxation in an organic solid, and the analysis of nonexponential relaxation. J Chem Phys 2012; 136:054508. [DOI: 10.1063/1.3677183] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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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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Stocchero M, Ferrarini A, Moro GJ, Dunmur DA, Luckhurst GR. Molecular theory of dielectric relaxation in nematic dimers. J Chem Phys 2004; 121:8079-97. [PMID: 15485272 DOI: 10.1063/1.1794071] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
This paper reports a theory for the dielectric relaxation of dimeric mesogenic molecules in a nematic liquid crystal phase. Liquid crystal dimers consist of two mesogenic groups linked by a flexible chain. Recent experimental studies [D. A. Dunmur, G. R. Luckhurst, M. R. de la Fuente, S. Diez, and M. A. Perez Jubindo, J. Chem. Phys. 115, 8681 (2001)] of the dielectric properties of polar liquid crystal dimers have found unexpected results for both the static (low frequency) and variable frequency dielectric response of these materials. The theory developed in this paper provides a quantitative model with which to understand the observed experimental results. The mean-square dipole moments of alpha,omega-bis[(4-cyanobiphenyl-4'-yl]alkanes in a nematic phase have been calculated using both the rotational isomeric state model and a full torsional potential for the carbon-carbon bonds of the flexible chain. The orienting effect of the nematic phase is taken into account by a parametrized potential of mean torque acting on the mesogenic groups and the segments in the flexible chain. Results of calculations using the full torsional potential are in excellent agreement with experimental results for comparable systems. The probability density p(eq)(beta(A),beta(B)) for the orientation of the mesogenic groups (A,B) along the nematic director is also calculated. The resultant potential of mean torque is a surface characterized by four deep energy wells or sites equivalent to alignment of the terminal groups A and B approximately parallel and antiparallel to the director; of course, the reversal of the director leads to equivalent sites. This potential energy surface provides the basis for a kinetic model of dielectric relaxation in nematic dimers. Solution of the Fokker-Planck equation corresponding to this four-site model gives the time dependence of the site populations, and hence the time-correlation functions for the total dipole moment along the director. In this model the end-over-end rotation of the molecule, corresponding to simultaneous reversal of both mesogenic groups, is excluded because the activation energy is too large. Results are presented for a number of cases, in which a dipole is located on one or both of the mesogenic groups, and additionally where the groups differ in size. For the latter, under particular conditions, the correlation function exhibits a biexponential decay, which corresponds to two low frequency absorptions in the dielectric spectrum. This is exactly what has been observed for nonsymmetric nematic dimers having different groups terminating a flexible chain. Experimental results over a range of temperature for the nonsymmetric dimer alpha-[(4-cyanobiphenyl)-4'-yloxy]-omega-(4-decylanilinebenzylidene-4'-oxy)nonane can be fitted precisely to the theory, which provides new insight into the orientational and conformational dynamics of molecules in ordered liquid crystalline phases.
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Affiliation(s)
- M Stocchero
- Dipartimento di Scienze Chimiche, University of Padua, via Marzolo 1, 35131 Padua, Italy
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Koksal F, Rossler E, Sillescu H. Spin-lattice relaxation by tunnelling motions of methyl groups in four acetates. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/15/28/014] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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19
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Clough S, Heidemann A, Horsewill AJ, Lewis JD, Paley MNJ. The rate of thermally activated methyl group rotation in solids. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/15/11/026] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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20
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Clough S, Horsewill AJ, McDonald PJ. Methyl tunnelling spectroscopy and level crossing phenomena in solid acetone. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/17/6/019] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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21
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Clough S, McDonald PJ. The correlation of methyl tunnelling and thermally activated reorientation: II. ACTA ACUST UNITED AC 2000. [DOI: 10.1088/0022-3719/15/29/003] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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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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Clough S. Unification of the quantum and classical theories of methyl NMR. SOLID STATE NUCLEAR MAGNETIC RESONANCE 1999; 14:73-79. [PMID: 10437660 DOI: 10.1016/s0926-2040(99)00016-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The existing low and high temperature theories of methyl NMR are not linked because two conditions imposed on state functions in the low temperature theory are not compatible with the classical rotations on which the high temperature theory is based. The conditions do not occur in a geometrical theory of quantum phenomena in which particles and waves have separate roles. When applied to methyl dynamics, this theory covers the whole temperature range.
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Affiliation(s)
- S Clough
- Department of Physics, School of Physics and Astronomy, University of Nottingham, UK
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27
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Kuhnen A, Vermathen P, Müller-Warmuth W. Methyl tunnelling, reorientation and NMR relaxation in solid acetates. SOLID STATE NUCLEAR MAGNETIC RESONANCE 1998; 10:161-168. [PMID: 9550344 DOI: 10.1016/s0926-2040(97)00025-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Rotational excitations of methyl groups in six solid acetates have been investigated by 1H nuclear magnetic resonance (NMR) relaxation time measurements at 15 MHz and 30 MHz and at temperatures between 10 K and the melting point. Hindering barriers between 1.6 kJ/mol and 3.7 kJ/mol have been found that could be correlated to the tunnelling frequencies observed by inelastic neutron scattering. A consistent description of the relaxation rate dependences from the classical regime at high temperatures to the quantum-mechanical regime at low temperatures is possible by Haupt's equation. The rotational potentials are mainly determined by inter-molecular interaction with an important influence of water of crystallization, if present.
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Affiliation(s)
- A Kuhnen
- Institut für Physikalische Chemie, der Westfälischen Wilhelms-Universität, Münster, Germany
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Abstract
Assumptions on which NMR dynamical studies have been based for nearly 50 years are consistent with a relative quantum theory based on Minkowski spacetime. A symmetry condition required by the existence of reference frames takes over the usual role of particle permutation symmetry, leaving a quantum theory of relative motion which only involves observables.
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Affiliation(s)
- S Clough
- Department of Physics, University of Nottingham, UK
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Jahnke TK, Müller-Warmuth W, Bennati M. Anomalous proton relaxation, rotational tunnelling and barriers to methyl group rotation in solid acetyl halides. SOLID STATE NUCLEAR MAGNETIC RESONANCE 1995; 4:153-161. [PMID: 7773648 DOI: 10.1016/0926-2040(94)00042-b] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Rotational excitations of methyl groups attached to carbonyl in solid acetic acid, acetyl fluoride, acetyl chloride and acetyl bromide have been investigated by 1H nuclear magnetic resonance (NMR) relaxation times and field-cycling measurements at two frequencies and various temperatures. The tunnel splittings have been found to occur between 3.3 and 0.08 mu eV making quantum effects important for the relaxation behaviour. For the acetyl halides, similar tunnelling and NMR frequencies lead to an anomalous-looking temperature dependence of the relaxation rates. A consistent description by Haupt's equation is possible. The rotational potentials have been derived from the data and compared with those obtained from microwave spectra of the corresponding isolated molecules. The hindering potential is purely three-fold and the barrier is dominated by the functional group.
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Affiliation(s)
- T K Jahnke
- Institut für Physikalische Chemie der Westfälischen Wilhelms-Universität, Münster, Germany
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