Temperaturabhängigkeit der Phosphor-HFS bei Iminophosphoran- Radikalen / Temperature Dependence of ESR-Phosphorus Coupling Constants of Iminophosphorane Radicals

1975 ◽  
Vol 30 (9) ◽  
pp. 1175-1180
Author(s):  
K. Scheffler ◽  
S. Hieke ◽  
R. Haller ◽  
H. B. Stegmann
Keyword(s):  
Temperature Dependence ◽  
Internal Rotation ◽  
Free Electron ◽  
Esr Spectra ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Temperature Dependent ◽  
Potential Barriers ◽  
Phosphorus Nucleus

ESR-spectra of iminophosphorane radicals exhibit a strong temperature dependent coupling constant of the phosphorus nucleus. This splitting is described by a superposition of π-σ- and hyperconjugative interactions with the free electron. Because of hindered internal rotation of the iminophosphorane group the hyperconjugation term becomes temperature dependent. Differences in the phosphorus data of ortho- and para-iminophosphorane radicals respectively may be explained by a change of the potential barriers hindering the internal rotation

19F Nuclear Quadrupole Coupling in some Halomethanes

1986 ◽  
Vol 41 (1-2) ◽  
pp. 171-174 ◽  
Author(s):  
M. Frank ◽  
F. Gubitz ◽  
W. Ittner ◽  
W. Kreische ◽  
A. Labahn ◽  
...  
Keyword(s):  
Angular Distribution ◽  
Simple Model ◽  
Temperature Dependence ◽  
Coupling Constants ◽  
Temperature Dependent ◽  
Distribution Method ◽  
Quadrupole Coupling ◽  
Time Differential ◽  
Nuclear Quadrupole

The 19F quadrupole coupling constants in CF4, CHF3, CClF3 and CHClF2 are reported. The measurements were carried out temperature dependent using the time differential perturbed angular distribution method (TDPAD). The temperature dependence can be satisfactorily described in the framework of the Bayer-Kushida theory. A simple model is used to explain the appearance of H-F and Cl-F coupling constants in CHF3/CHClF2 and CClF3, respectively.

EFFECTS OF TEMPERATURE-DEPENDENT COUPLING CONSTANT EVOLUTION ON THE UNIFICATION SCALE

1987 ◽  
Vol 02 (07) ◽  
pp. 479-485 ◽  
Author(s):  
K. ENQVIST ◽  
K. KAJANTIE
Keyword(s):  
Gauge Coupling ◽  
Coupling Constants ◽  
Thermal Bath ◽  
Coupling Constant ◽  
Temperature Dependent ◽  
Cosmological Context ◽  
Effects Of Temperature

We discuss how the evolution of gauge coupling constants is affected by a thermal bath, the existence of which is natural to assume in a cosmological context. The temperature dependent renormalization prescription induced by the thermal bath can cause sizeable effects, and the unification scale is shifted from the value computed from the coupling constant evolution in vacuum.

Internal barriers to rotation in 2,6-difluoroisopropyl and 2,6-difluoroethylbenzenes. Overlap of dynamic nuclear magnetic resonance (DNMR) and the J method

1982 ◽  
Vol 60 (20) ◽  
pp. 2611-2616 ◽  
Author(s):  
Ted Schaefer ◽  
Richard P. Veregin ◽  
Reino Laatikainen ◽  
Rudy Sebastian ◽  
Kirk Marat ◽  
...  
Keyword(s):  
Internal Rotation ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Temperature Dependent ◽  
Carbon Carbon Bond ◽  
Barrier Region ◽  
Yield Formula ◽  
Internal Barriers ◽  
Dynamic Nuclear Magnetic Resonance ◽  
Spin Spin Coupling

The temperature-dependent 19F nmr spectra of 2,6-difluoroisopropylbenzene yield [Formula: see text], ΔH≠, and ΔS≠ as 6.93 (5) kcal/mol, 6.1(1) kcal/mol, and −5.0(8) cal/mol K, respectively, for the internal rotation of the isopropyl group about the sp2–sp3 carbon–carbon bond. The long-range spin–spin coupling constant over six bonds, 6JpH,CH, combined with the J method gives a twofold internal potential barrier of 5.0 ± 1.6 kcal/mol at 305 K. Although in this barrier range the J method suffers from large errors, the two methods yield comparable values for the barrier height. The lineshape method is inapplicable to 2,6-difluoroefhylbenzene. The J method finds the preferred conformation and a twofold barrier of 6.0 ± 2 kcal/mol, again in a barrier region where this method is inaccurate. Relative to hydrogen, the fluorine substituents cause substantial increases in the barriers to internal rotation. Signs of the stereospecific couplings, 4JoF,CH, are determined.

THE CRYSTAL FIELD EFFECTS ON THE PHASE DIAGRAMS OF THE SPIN-2 BILAYER BETHE LATTICE

2008 ◽  
Vol 22 (27) ◽  
pp. 4877-4898 ◽  
Author(s):  
ERHAN ALBAYRAK ◽  
SEYMA AKKAYA ◽  
SABAN YILMAZ
Keyword(s):  
Phase Transitions ◽  
Phase Diagrams ◽  
Crystal Field ◽  
Ground State ◽  
Bethe Lattice ◽  
Interlayer Coupling ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Temperature Dependent ◽  
Field Interaction

The bilayer spin-2 Ising model on the Bethe lattice is investigated by taking into account the intralayer coupling constants of the two layers J1 and J2, interlayer coupling constant between the layers J3 and crystal field interaction Δ by using the exact recursion equations in a pairwise approach. The ground state (GS) phase diagrams of the model are obtained on the (J2/|J1|, J3/q|J1|) planes for given Δ values and on the (Δ/qJ, J3/qJ) plane when J1 = J2 = J, and thus 33 distinct GS configurations are found. The temperature-dependent phase diagrams are obtained for J1 > 0, J2 > 0, and for J3 > 0 or J3 < 0 on the (kT/J1, J3/J1) planes for given Δ/qJ1 and J2/J1 and on the (Δ/J, kT/J) plane for given J3/J when J1 = J2 = J for the coordination number q = 3. It was found that the system exhibits both first- and second-order phase transitions and tricritical points. The paramagnetic phases are also classified by studying the thermal variations of the quadrupolar moments.

Konformationsuntersuchungen durch Elektronenspinresonanz Two-Jump-prozesse in Benzyl-phosphonium Salzen / Conformation Studies by Electron Spin Resonance Two-Jump Process in Benzyl-phosphonium Salts

1976 ◽  
Vol 31 (12) ◽  
pp. 1620-1629
Author(s):  
Klaus Scheffler ◽  
Klaus Hieke ◽  
Paul Schüler ◽  
Hartmut B. Stegmann
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Jump Process ◽  
Esr Spectra ◽  
Coupling Constants ◽  
Phosphonium Salts ◽  
Hindered Rotation ◽  
Limit Value ◽  
Spin Resonance ◽  
Phosphorus Nucleus

AbstractThe ESR spectra of 4-oxyl-benzyl-phosphonium-bromide radicals show a temperature dependence of the methylene protons and the phosphorus nucleus coupling constants which is explained by a hindered rotation of the phenoxyl ring of the radicals. Furthermore compounds with different phosphor substituents exhibit the phenomenon of a two jump process. This effect is described by an isomerisation of two symmetric radical conformations. Activation energies for this process are found to be around 7 kcal/Mol. The conformation of the radicals can be discussed as staggered ethane analogues. A lower limit value for the hyperconjugation Bᴾ -parameter is proposed.

2-Phenyladamantane as a model for axial phenylcyclohexane. 1H NMR and molecular orbital studies of motion about the Csp2—Csp3 bond

1991 ◽  
Vol 69 (3) ◽  
pp. 503-508 ◽  
Author(s):  
Ted Schaefer ◽  
Christian Beaulieu ◽  
Rudy Sebastian
Keyword(s):  
Internal Rotation ◽  
Nmr Spectra ◽  
Opposite Sign ◽  
Symmetry Plane ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Key Words 2 ◽  
H Nmr ◽  
Carbon Carbon Bond ◽  
Internal Mobility

The 1H NMR spectra of the aromatic groups of 2-phenylcyclohexane and 2-phenyladamantane, in CS2/C6D12 solution at 300 K, are analyzed to yield the long-range coupling constants between the α and ring protons. The coupling over six bonds is related to the internal rotational potential about the Csp2—Csp3 bond in these molecules. It is confirmed that the equatorial isomer of phenylcyclohexane has the parallel conformer, that in which the aromatic plane lies in the symmetry plane bisecting the cyclohexane moiety, as the most stable. The apparent twofold barrier to rotation about the exocyclic carbon–carbon bond follows as 7.1 kJ/mol from the six-bond coupling constant. For 2-phenyladamantane, the six-bond coupling constant strongly implies that the perpendicular conformer, perhaps slightly skewed, is that of lowest energy and that the apparent twofold barrier to rotation about the Csp2—Csp3 bond is about 7.5 kJ/mol. Insofar as 2-phenyladamantane mimics axial phenylcyclohexane, these results confirm recent conclusions about the conformation of the latter and provide evidence for its internal mobility. Geometry-optimized AMI and STO-3G MO computations are reported for the internal motion in both isomers of phenylcyclohexane. The former agree best with experiment for the equatorial isomer, but both imply a significant fourfold, of opposite sign to the twofold, component of the internal rotational potential. For the axial isomer, the two sets of computations find a skewed perpendicular conformer as most stable, in rough agreement with force-field results. However, the barrier to rotation about the Csp2—Csp3 bond is computed as small and AMI has the parallel conformer as more stable than the perpendicular. Key words: 2-phenyladamantane, 1H NMR and internal rotation; phenylcyclohexane, 1H NMR and internal rotation; MO computations, 2-phenyladamantane and phenylcyclohexane.

The conformational behaviour of 2-fluoro and of 2,6-difluoroacetophenone implied by proximate spin–spin coupling constants and MO calculations

1985 ◽  
Vol 63 (8) ◽  
pp. 2256-2260 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner ◽  
Timothy A. Wildman ◽  
James Peeling
Keyword(s):  
Temperature Dependence ◽  
Geometry Optimization ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Population Distributions ◽  
Carbon Carbon Bond ◽  
Acetyl Group ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The temperature dependence of [Formula: see text], the nuclear spin–spin coupling constant over five formal bonds between the methyl protons and the 19F nucleus in 2-fluoroacetophenone and 2,6-difluoroacetophenone, is modelled on the assumption that 5J is a proximate coupling and that the STO 3G MO potential functions describe the population distributions of the rotamers defined by rotation about the exocyclic sp2–sp2 carbon–carbon bond. It is assumed that 5J has a cos4 θ dependence between 0 and 90°, where θ is the angle by which the acetyl group twists out of the plane of the benzene plane. The potential function is obtained from extensive geometry optimization procedures for a range of θ values. At 305 K, nonplanar conformations are substantially populated in 2-fluoroacetophenone, according to this model, which is also consistent with the idea that the 2,6-difluoro derivative has a markedly nonplanar ground state. The model reproduces the large 5J in the monofluoro relative to the difluoro compound, as well as the much larger temperature dependence in the former.

Temperature dependence of the 59Co quadrupole coupling constant in K3Co(CN)6

1980 ◽  
Vol 58 (1) ◽  
pp. 68-73 ◽  
Author(s):  
J. A. J. Lourens ◽  
E. Smit
Keyword(s):  
Temperature Dependence ◽  
Structural Phase ◽  
Intermediate Frequency ◽  
Quadrupole Coupling Constant ◽  
Coupling Constants ◽  
Positive Contribution ◽  
Coupling Constant ◽  
Quadrupole Coupling ◽  
Bond Stretching ◽  
Modes Of Vibration

Expressions are presented for calculating the effects of bond-stretching and rotational modes of vibration on the temperature dependence of quadrupole coupling constants in crystals. Contributions to the motional averaging of the electric field gradient tensor arising from point charges, point dipoles, and overlap of closed wave functions are evaluated and the resulting expressions applied to analyse the temperature variation of the 59Co quadrupole coupling constant in K3Co(CN)6. Both stretching and rotational internal modes of vibration of the Co(CN)6 octahedron had to be taken into account to analyse the data. In particular, an intermediate frequency mode of wavenumber 414 cm−1 has been found to make a substantial and positive contribution to the shift in coupling constant arising from the low (~ 100 cm−1) and intermediate frequency (~ 400 cm−1) modes. The remainder of the shift (~ 90%) has been attributed to a rotary mode of wavenumber 26 cm−1. The extracted temperature dependence of this mode points to the possible existence of a structural phase transition in K3Co(CN)6 below 100 K.

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