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Peter A Beckmann - One of the best experts on this subject based on the ideXlab platform.
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methyl and t Butyl Group rotation in a molecular solid 1h nmr spin lattice relaxation and x ray diffraction
Physical Chemistry Chemical Physics, 2016Co-Authors: Peter A Beckmann, Curtis E Moore, Arnold L. RheingoldAbstract:We report solid state 1H nuclear magnetic resonance spin-lattice relaxation experiments and X-ray diffractometry in 2-t-Butyldimethylsilyloxy-6-bromonaphthalene. This compound offers an opportunity to simultaneously investigate, and differentiate between, the rotations of a t-Butyl Group [C(CH3)3] and its three constituent methyl Groups (CH3) and, simultaneously, a pair of ‘lone’ methyl Groups (attached to the Si atom). The solid state 1H relaxation experiments determine activation energies for these rotations. We review the models for the dynamics of both ‘lone’ methyl Groups (ones whose rotation axes do not move on the NMR time scale) and models for the dynamics of the t-Butyl Group and its constituent methyl Groups (whose rotation axes reorient on the NMR time scale as the t-Butyl Group rotates).
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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
Journal of Chemical Physics, 2014Co-Authors: Xianlong Wang, Frank B Mallory, C W Mallory, Hosanna R Odhner, Peter A BeckmannAbstract: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 1H 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 1H 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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a proton spin lattice relaxation rate study of methyl and t Butyl Group reorientation in the solid state
Solid State Nuclear Magnetic Resonance, 2010Co-Authors: Laura C Popa, Arnold L. Rheingold, Peter A BeckmannAbstract:We have measured the solid state nuclear magnetic resonance (NMR) 1H spin-lattice relaxation rate from 93 to 340 K at NMR frequencies of 8.5 and 53 MHz in 5-t-Butyl-4-hydroxy-2-methylphenyl sulfide. We have also determined the molecular and crystal structures from X-ray diffraction experiments. The relaxation is caused by methyl and t-Butyl Group rotation modulating the spin-spin interactions and we relate the NMR dynamical parameters to the structure. A successful fit of the data requires that the 2-methyl Groups are rotating fast (on the NMR time scale) even at the lowest temperatures employed. The rotational barrier for the two out-of-plane methyl Groups in the t-Butyl Groups is 14.3+/-2.7 kJ mol(-1) and the rotational barrier for the t-Butyl Groups and their in-plane methyl Groups is 24.0+/-4.6 kJ mol(-1). The uncertainties account for the uncertainties associated with the relationship between the observed NMR activation energy and a model-independent barrier, as well as the experimental uncertainties.
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the relationship between crystal structure and methyl and t Butyl Group dynamics in van der waals organic solids
Journal of Chemical Physics, 2004Co-Authors: Peter A Beckmann, C S Paty, Elizabeth Allocco, Maria Herd, Carolyn Kuranz, Arnold L. RheingoldAbstract:We report x-ray diffractometry in a single crystal of 2-t-Butyl-4-methylphenol (TMP) and low-frequency solid state nuclear magnetic resonance (NMR) proton relaxometry in a polycrystalline sample of TMP. The x-ray data show TMP to have a monoclinic, P21/c, structure with eight molecules per unit cell and two crystallographically inequivalent t-Butyl Group (C(CH3)3) sites. The proton spin-lattice relaxation rates were measured between 90 and 310 K at NMR frequencies of 8.50, 22.5, and 53.0 MHz. The relaxometry data is fitted with two models characterizing the dynamics of the t-Butyl Groups and their constituent methyl Groups, both of which are consistent with the determined x-ray structure. In addition to presenting results for TMP, we review previously reported x-ray diffractometry and low-frequency NMR relaxometry in two other van der Waals solids which have a simpler structure. In both cases, a unique model for the reorientational dynamics was found. Finally, we review a similar previously reported analy...
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methyl and t Butyl Group reorientation in planar aromatic solids low frequency nuclear magnetic resonance relaxometry and x ray diffraction
Journal of Chemical Physics, 2003Co-Authors: Peter A Beckmann, Frank B Mallory, Carolyn A Buser, Kathleen Gullifer, Clelia W Mallory, Gene Rossi, Arnold L. RheingoldAbstract:We have synthesized 3-t-Butylchrysene and measured the Larmor frequency ω/2π (= 8.50, 22.5, and 53.0 MHz) and temperature T (110–310 K) dependence of the proton spin–lattice relaxation rate R in the polycrystalline solid [low-frequency solid state nuclear magnetic resonance (NMR) relaxometry]. We have also determined the molecular and crystal structure in a single crystal of 3-t-Butylchrysene using x-ray diffraction, which indicates the presence of a unique t-Butyl Group environment. The spin-1/2 protons relax as a result of the spin–spin dipolar interactions being modulated by the superimposed reorientation of the t-Butyl Groups and their constituent methyl Groups. The reorientation is successfully modeled by the simplest motion; that of random hopping describable by Poisson statistics. The x-ray data indicate near mirror-plane symmetry that places one methyl Group nearly in the aromatic plane and the other two almost equally above and below the plane. The NMR relaxometry data indicate that the nearly in...
Arnold L. Rheingold - One of the best experts on this subject based on the ideXlab platform.
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methyl and t Butyl Group rotation in a molecular solid 1h nmr spin lattice relaxation and x ray diffraction
Physical Chemistry Chemical Physics, 2016Co-Authors: Peter A Beckmann, Curtis E Moore, Arnold L. RheingoldAbstract:We report solid state 1H nuclear magnetic resonance spin-lattice relaxation experiments and X-ray diffractometry in 2-t-Butyldimethylsilyloxy-6-bromonaphthalene. This compound offers an opportunity to simultaneously investigate, and differentiate between, the rotations of a t-Butyl Group [C(CH3)3] and its three constituent methyl Groups (CH3) and, simultaneously, a pair of ‘lone’ methyl Groups (attached to the Si atom). The solid state 1H relaxation experiments determine activation energies for these rotations. We review the models for the dynamics of both ‘lone’ methyl Groups (ones whose rotation axes do not move on the NMR time scale) and models for the dynamics of the t-Butyl Group and its constituent methyl Groups (whose rotation axes reorient on the NMR time scale as the t-Butyl Group rotates).
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a proton spin lattice relaxation rate study of methyl and t Butyl Group reorientation in the solid state
Solid State Nuclear Magnetic Resonance, 2010Co-Authors: Laura C Popa, Arnold L. Rheingold, Peter A BeckmannAbstract:We have measured the solid state nuclear magnetic resonance (NMR) 1H spin-lattice relaxation rate from 93 to 340 K at NMR frequencies of 8.5 and 53 MHz in 5-t-Butyl-4-hydroxy-2-methylphenyl sulfide. We have also determined the molecular and crystal structures from X-ray diffraction experiments. The relaxation is caused by methyl and t-Butyl Group rotation modulating the spin-spin interactions and we relate the NMR dynamical parameters to the structure. A successful fit of the data requires that the 2-methyl Groups are rotating fast (on the NMR time scale) even at the lowest temperatures employed. The rotational barrier for the two out-of-plane methyl Groups in the t-Butyl Groups is 14.3+/-2.7 kJ mol(-1) and the rotational barrier for the t-Butyl Groups and their in-plane methyl Groups is 24.0+/-4.6 kJ mol(-1). The uncertainties account for the uncertainties associated with the relationship between the observed NMR activation energy and a model-independent barrier, as well as the experimental uncertainties.
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the relationship between crystal structure and methyl and t Butyl Group dynamics in van der waals organic solids
Journal of Chemical Physics, 2004Co-Authors: Peter A Beckmann, C S Paty, Elizabeth Allocco, Maria Herd, Carolyn Kuranz, Arnold L. RheingoldAbstract:We report x-ray diffractometry in a single crystal of 2-t-Butyl-4-methylphenol (TMP) and low-frequency solid state nuclear magnetic resonance (NMR) proton relaxometry in a polycrystalline sample of TMP. The x-ray data show TMP to have a monoclinic, P21/c, structure with eight molecules per unit cell and two crystallographically inequivalent t-Butyl Group (C(CH3)3) sites. The proton spin-lattice relaxation rates were measured between 90 and 310 K at NMR frequencies of 8.50, 22.5, and 53.0 MHz. The relaxometry data is fitted with two models characterizing the dynamics of the t-Butyl Groups and their constituent methyl Groups, both of which are consistent with the determined x-ray structure. In addition to presenting results for TMP, we review previously reported x-ray diffractometry and low-frequency NMR relaxometry in two other van der Waals solids which have a simpler structure. In both cases, a unique model for the reorientational dynamics was found. Finally, we review a similar previously reported analy...
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Remote Rotamer Control: The Effect of a 4‐tert‐Butyl Group on the Coordination Chemistry of TpR Ligands
European Journal of Inorganic Chemistry, 2003Co-Authors: Arnold L. Rheingold, Louise M. Liable-sands, James A. Golan, Swiatoslaw TrofimenkoAbstract:Three novel homoscorpionate ligands containing a tert-Butyl Group in the 4-position have been synthesized: hydrotris(4-tert-Butylpyrazol-1-yl)borate (Tp4tBu), hydrotris(4-tert-Butyl-3-p-tolylpyrazol-1-yl)borate (TpTol,4tBu), and hydrotris(4-tert-Butyl-3-isopropylpyrazol-1-yl)borate (TpiPr,4tBu). The 4-tert-Butyl Group does not alter the coordination chemistry of the first two ligands, relative to their 4-H analogues, however, the coordination chemistry of the third ligand is dramatically changed, making it a “tetrahedral enforcer”. The complexes Co[Tp4tBu][TpNp] (1), Tl[TpTol,4tBu] (2), Rh[TpTol,4tBu](CO)2 (3), Co[TpiPr,4tBu]Cl (4), Co[TpiPr,4tBu]N3 (5) and Co[TpiPr,4tBu]NCS (6) have been structurally characterized. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
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methyl and t Butyl Group reorientation in planar aromatic solids low frequency nuclear magnetic resonance relaxometry and x ray diffraction
Journal of Chemical Physics, 2003Co-Authors: Peter A Beckmann, Frank B Mallory, Carolyn A Buser, Kathleen Gullifer, Clelia W Mallory, Gene Rossi, Arnold L. RheingoldAbstract:We have synthesized 3-t-Butylchrysene and measured the Larmor frequency ω/2π (= 8.50, 22.5, and 53.0 MHz) and temperature T (110–310 K) dependence of the proton spin–lattice relaxation rate R in the polycrystalline solid [low-frequency solid state nuclear magnetic resonance (NMR) relaxometry]. We have also determined the molecular and crystal structure in a single crystal of 3-t-Butylchrysene using x-ray diffraction, which indicates the presence of a unique t-Butyl Group environment. The spin-1/2 protons relax as a result of the spin–spin dipolar interactions being modulated by the superimposed reorientation of the t-Butyl Groups and their constituent methyl Groups. The reorientation is successfully modeled by the simplest motion; that of random hopping describable by Poisson statistics. The x-ray data indicate near mirror-plane symmetry that places one methyl Group nearly in the aromatic plane and the other two almost equally above and below the plane. The NMR relaxometry data indicate that the nearly in...
Christian Schroder - One of the best experts on this subject based on the ideXlab platform.
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effect of a tertiary Butyl Group on polar solvation dynamics in aqueous solution a computational approach
Journal of Physical Chemistry B, 2017Co-Authors: Esther Heid, Christian SchroderAbstract:The current computational study investigates the changes in solvation dynamics of water when introducing hydrophobic side chains to the molecular probe N-methyl-6-oxyquinolinium betaine. High-precision transient fluorescence and absorption measurements published in the companion article (10.1021/acs.jpcb.7b05031) revealed an influence of hydrophobic side chain alterations on the observed solvation dynamics of a chromophore in water. As the influence of shape, size, and structure of chromophores on the time-dependent Stokes shift was so far thought to play a role only in slowly rotating solvents compared to the solute or if the hydrogen bonding ability of the solute changes, this finding is quite unexpected. Analysis of the time-dependent Stokes shift obtained from nonequilibrium simulations corroborates experimental retardation factors and activation energies, and indicates that solute motion, namely vibration, is mainly responsible for the observed retardation of solvation dynamics. The faster dynamics a...
Masahiko Hayashi - One of the best experts on this subject based on the ideXlab platform.
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simple preparation of β amino alcohols possessing a tert Butyl Group at the α carbon
ChemInform, 2012Co-Authors: James T. Zacharia, Takanori Tanaka, Yumiko Uesaka, Masahiko HayashiAbstract:Among the title compounds, derivatives (Ic) and (Id) which bear the tert-Butyl Group at the α-carbon, are shown to be efficient catalysts for the asymmetric addition of diethylzinc to benzaldehyde.
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Simple Preparation of β‐Amino Alcohols Possessing a tert‐Butyl Group at the α‐Carbon.
ChemInform, 2012Co-Authors: James T. Zacharia, Takanori Tanaka, Yumiko Uesaka, Masahiko HayashiAbstract:Among the title compounds, derivatives (Ic) and (Id) which bear the tert-Butyl Group at the α-carbon, are shown to be efficient catalysts for the asymmetric addition of diethylzinc to benzaldehyde.
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Simple Preparation of β-Amino Alcohols Possessing a tert-Butyl Group at the α-Carbon
Synthesis, 2012Co-Authors: James T. Zacharia, Takanori Tanaka, Yumiko Uesaka, Masahiko HayashiAbstract:Simple preparation of β-amino alcohols possessing a tert -Butyl Group at the α-carbon was achieved. These β-amino alcohols proved to work effectively as catalysts in the enantioselective alkylation of aldehydes.
N P Ernsting - One of the best experts on this subject based on the ideXlab platform.
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effect of a tertiary Butyl Group on polar solvation dynamics in aqueous solution femtosecond fluorescence spectroscopy
Journal of Physical Chemistry B, 2017Co-Authors: Mario Gerecke, Celin Richter, Martin Quick, Ilya N Ioffe, Rainer Mahrwald, Sergey A Kovalenko, N P ErnstingAbstract:We monitor the time-dependent Stokes shift (TDSS) of fluorescence from the zwitterionic probe N-methyl-6-oxyquinolinium betaine in water. A spectral relaxation time τsolv = 0.57 ps (at 20.5 °C) is attributed to a solvation process involving water in the hydration layer. In this article we show that a tertiary Butyl Group, when attached to the chromophore, slows the dynamics to τsolv = 0.76 ps and increases the corresponding activation energy by 5 kJ/mol. In a companion paper (10.1021/acs.jpcb.7b05039), simulations suggest that the observed slow-down indicates coupling of solute vibrations to hydration water. Thus, a new angle on a thoroughly researched topic, solvation dynamics, has been opened.
