"Through-space" spin–spin coupling between thallium and fluorine in fluorophenylthallium compounds

1989 ◽  
Vol 67 (11) ◽  
pp. 1847-1850
Author(s):  
Gerald Norman Pecksen ◽  
Raymond Frederick Martin White
Keyword(s):  
Coupling Constants ◽  
Spin Coupling ◽  
Methyl Group ◽  
Fluorine Nmr ◽  
Thallium Atom ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Thallium to fluorine spin–spin coupling constants have been measured for a number of fluoro- and trifluoro-methyl-substituted mono- and di-arylthallium derivatives. The results provide evidence of "through-space" coupling in the diaryl derivatives when the fluoro- or trifluoro-methyl group is ortho to the thallium atom. Keywords: thallium, fluorine, NMR, through-space coupling.

Concerning the mechanism of in toluene and its derivatives

1983 ◽  
Vol 61 (12) ◽  
pp. 2785-2789 ◽  
Author(s):  
Ted Schaefer ◽  
Reino Laatikainen
Keyword(s):  
Coupling Constants ◽  
Spin Coupling ◽  
Similar Magnitude ◽  
Conformational Preference ◽  
Conformational Studies ◽  
Methyl Group ◽  
Ring Substituent ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of

On the basis of the observed five-bond spin–spin coupling constants between the α protons and the meta ring protons in the 2,6-difluoro derivatives of toluene, ethylbenzene, and cumene, it is argued that [Formula: see text] in toluene can be written as A[Formula: see text]. A and B are of the same sign and of very similar magnitude. In consequence, [Formula: see text] cannot be used to measure the conformational preference of the methyl group. However, [Formula: see text] and [Formula: see text] in α-substituted toluene derivatives will be useful in conformational studies. [Formula: see text] in toluene derivatives varies between 0.30 and 0.46 Hz and some patterns in its ring substituent dependence can be gleaned from some fifty precise values.

Long-range 13C,1H and 13C,19F coupling constants as indicators of the conformational properties of 4-fluoroanisole, 2,3,5,6-tetrafluoroanisole, and pentafluoroanisole

1984 ◽  
Vol 62 (8) ◽  
pp. 1592-1597 ◽  
Author(s):  
Ted Schaefer ◽  
Reino Laatikainen ◽  
Timothy A. Wildman ◽  
James Peeling ◽  
Glenn H. Penner ◽  
...  
Keyword(s):  
Long Range ◽  
Methoxy Group ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Dynamic Nmr ◽  
Methyl Group ◽  
Conformational Properties ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Rotor Model

Long-range spin–spin coupling constants over six bonds between 13C nuclei in the methyl group and ring protons or 19F nuclei in the para position are reported for 4-fluoroanisole, 2,3,5,6-tetrafluoroanisole, and pentafluoroanisole in solution. The couplings are σ–π electron mediated, as indicated by INDO MO FPT computations and by measurements on anisole, 2,6-dibromoanisole, 2,6-dichloroanisole, 2,6-dibromo-4-fluoroanisole, and 2,6-dibromo-4-methylanisole. On the basis of the measured coupling magnitudes and a hindered rotor model, it is concluded that the barrier to internal rotation about the [Formula: see text] bond in 4-fluoroanisole lies near 6 kcal/mol, is nearly zero in the tetrafluoroanisole, and is somewhat less than 1 kcal/mol in the pentafluoroanisole. In the latter, the preferred conformation is that in which the methoxy group lies in a plane perpendicular to the pentafluorophenyl plane. Some inconclusive dynamic nmr experiments on anisole, including T1ρ measurements, are briefly discussed.

Sigma and Pi Electron Contributions to Long-range Spin–Spin Coupling Constants in the Methyl Derivatives of the Fluoropyridines

1972 ◽  
Vol 50 (14) ◽  
pp. 2344-2350 ◽  
Author(s):  
J. B. Rowbotham ◽  
T. Schaefer
Keyword(s):  
Nitrogen Atom ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
Methyl Group ◽  
Spin Coupling Constants ◽  
Methyl Derivatives ◽  
Spin Spin Coupling ◽  
Derivatives Of

Seven methyl derivatives of the 3- and 4-fluoropyridines are synthesized and their p.m.r. spectra are analyzed. The nuclear spin–spin coupling constants are compared with previous results for the four methyl derivatives of 2-fluoropyridine. A model in which the nitrogen atom polarizes primarily the σ electron system of the ring, leaving the π electron contribution to the coupling mechanism relatively unaffected, qualitatively accounts for the large majority of the coupling constants. For example, the coupling over six bonds between methyl protons and a fluorine nucleus, [Formula: see text] is the same whether the fluorine atom or the methyl group is placed ortho to the nitrogen atom and is little different from its value in p-fluorotoluene. The model is consistent with significant σ electron contributions to long-range couplings over four and five bonds from methyl protons to fluorine nuclei or ring protons. Evidence is adduced for resonance structures in which fluorine conjugates with nitrogen or with ring carbon atoms. An earlier suggestion, that hyperconjugation of the methyl group with nitrogen is necessary to the interpretation of the observed couplings, is dropped. Instead, a substantial polarization of the σ electron core near C-2 and -6 is invoked but apparently does not extend appreciably beyond these atoms in the ring.

Long-range 1H, 19F spin–spin coupling constants in benzenesulfonyl fluoride and some of its derivatives. Insensitivity of 19F shifts to ortho substituents

1978 ◽  
Vol 56 (13) ◽  
pp. 1717-1720 ◽  
Author(s):  
Ted Schaefer ◽  
William J. E. Parr
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Van Der Waals Interactions ◽  
Methyl Group ◽  
Nuclear Magnetic Resonance Spectra ◽  
Replacement Technique ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Marked Dependence

The proton and 19F high resolution nuclear magnetic resonance spectra of benzenesulfonyl fluoride and of some derivatives are analyzed to yield spin–spin coupling constants between 19F and the ring protons. These parameters display a marked dependence on the ring substituents and it is not clear how their conformational behaviour can be distinguished from intrinsic substituent perturbations. The large magnitudes of the couplings over six bonds to the para protons, relative to those in benzoyl fluoride, strongly indicate the importance of conformations in which the S—F bond does not lie in the benzene plane. The methyl group replacement technique suggests that the six-bond coupling contains contributions in addition to that from a σ–π mechanism. The chemical shift of the para proton yields a π electron density at the contiguous carbon atom which is considerably smaller than in nitrobenzene, for example. The 19F shifts are much less sensitive to ortho substituents than are the 19F shifts in benzoyl fluoride derivatives, implying much smaller intramolecular van der Waals interactions in the sulfonyl compounds.

The proximate coupling constant, 5J(H,CH3), and the torsional mobility of the thiomethyl group in some thioanisole derivatives

1991 ◽  
Vol 69 (4) ◽  
pp. 620-624 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Salman R. Salman ◽  
James D. Baleja ◽  
Glenn H. Penner ◽  
...  
Keyword(s):  
Bond Order ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Torsional Motion ◽  
Coupling Constant ◽  
Methyl Group ◽  
H Nmr ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Ortho Substituent

The proximate coupling constants, 5J, between ortho and methyl protons in thioanisole and 18 of its derivatives are discussed as conformational indicators. On the assumption that 5J varies as cos4θ, for 0° ≤ θ ≤ 90°, θ being the angle by which the methyl group twists out of the aromatic plane, 5J for θ = 0° follows as −0.43 (2) Hz from the known internal barrier in thioanisole in solution. A measurement of 5J in meta- or para-substituted thioanisole derivatives then yields an approximate value for the twofold barrier to rotation about the Csp2—S bond. For derivatives containing an ortho substituent, 5J yields an estimate of the torsion angle for the thiomethyl moiety. In some instances these angles are compared with those derived from long-range 1H, 13C and 13C, 13C coupling constants. The size of the ortho substituent appears to have only a small effect on the magnitude of 5J. The major determinant of the latter appears to be the manner in which the substituent perturbs the mobile bond order of the Csp2—S bond. Key words: spin–spin coupling constants, thioanisole derivatives; 1H NMR, thioanisole derivatives; conformations, thioanisole derivatives; conformations, torsional motion of SCH3 group.

Vibrational and thermal averaging of the indirect nuclear spin-spin coupling constants of CH4, SiH4, GeH4 and SnH4

1997 ◽  
Vol 91 (5) ◽  
pp. 897-907 ◽  
Author(s):  
SHEELA KIRPEKAR ◽  
THOMAS ENEVOLDSEN ◽  
JENS ODDERSHEDE ◽  
WILLIAM RAYNES
Keyword(s):  
Nuclear Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Structural Characterization of Natural Products By Means of Quantum Chemical Calculations of NMR Parameters: New insights

2021 ◽  
Author(s):  
Fabio Luiz Paranhos Costa ◽  
Ana Carolina Ferreira de Albuquerque ◽  
Rodolfo Goetze Fiorot ◽  
Luciano Morais Lião ◽  
Lucas Haidar Martorano ◽  
...  
Keyword(s):  
Natural Products ◽  
Structural Characterization ◽  
Quantum Chemical ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nmr Parameters ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The calculation of NMR parameters for natural products was pioneered by Bifulco and coworkers in 2002. Since then, modelling 1H and 13C chemical shifts and spin-spin coupling constants for this...

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