Solvent-induced changes in 2J(H, F) for fluoroform via van der Waals interactions. Non-contact contributions to spin–spin coupling constants involving a proton?

1979 ◽  
Vol 57 (14) ◽  
pp. 1877-1880 ◽  
Author(s):  
Ted Schaefer ◽  
Harold M. Hutton ◽  
Salman R. Salman
Keyword(s):  
Van Der Waals ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Van Der Waals Interactions ◽  
Spin Orbital ◽  
Orbital Contribution ◽  
Solvent Interactions ◽  
Spin Coupling Constants ◽  
Induced Changes ◽  
Spin Spin Coupling

The spin–spin coupling between the proton and the fluorine nuclei, 2J, in fluoroform varies by 1% in a range of solvents. It is argued that 2J decreases algebraically as the van der Waals solute–solvent interactions increase in magnitude. Such a decrease is also observed for coupling constants which likely contain a substantial positive orbital contribution. If the van der Waals interactions perturb the spin–orbital term in J, then 2J in fluoroform may well contain orbital contributions, as recently calculated for 2J in methyl fluoride. In that event, the large discrepancies between observed 2J(H,F) values and those calculated by semiempirical theories of the contact term may be partially attributed to the neglect of orbital terms.

Proton and fluorine magnetic resonance studies of some benzoyl fluoride derivatives. Sensitivity of the fluorine shifts to intramolecular van der Waals interactions and steric effects

1977 ◽  
Vol 55 (22) ◽  
pp. 3936-3941 ◽  
Author(s):  
Ted Schaefer ◽  
Kirk Marat ◽  
Kalvin Chum ◽  
Alexander F. Janzen
Keyword(s):  
Magnetic Resonance ◽  
Van Der Waals ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Van Der Waals Interactions ◽  
Proton Proton ◽  
Out Of Plane ◽  
Spin Coupling Constants ◽  
The Individual ◽  
Spin Spin Coupling

The syntheses and the analyses of the high resolution proton and fluorine magnetic resonance spectra of the 3-fluoro-4-methyl-, 2-fluoro-5-chloro-, 2-fluoro-6-chloro-, 2,6-difluoro-, and of the pentafluorobenzoyl fluorides are reported. The spin–spin coupling constants over five bonds between the sidechain fluorine-19 and the ring protons are sensitive to intrinsic substituent perturbations. Their use in the deduction of conformational preferences is much more problematical than is the use of the corresponding proton–proton couplings in benzaldehyde derivatives. The 2-fluoro-6-chloro compound is nonplanar, as indicated by a finite magnitude of the long-range proton–fluorine coupling over six bonds. The nonplanarity is also indicated by a comparison of the through-space fluorine–fluorine coupling to those in the other compounds. The chemical shift of the sidechain fluorine moves to low field by over 35 ppm as the size of the two ortho substituents increases. The individual shifts are discussed in terms of intramolecular van der Waals interactions and of out-of-plane twisting of the COF group.

Revealing the specific solute–solvent interactions via the measurements of the NMR spin–spin coupling constants

2015 ◽  
Vol 1083 ◽  
pp. 175-178 ◽  
Author(s):  
Astghik A. Shahkhatuni ◽  
Aleksan G. Shahkhatuni ◽  
Nune S. Minasyan ◽  
Henry A. Panosyan ◽  
Aleksandr B. Sahakyan
Keyword(s):  
Coupling Constants ◽  
Spin Coupling ◽  
Solvent Interactions ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Density Functional Theory (DFT) Calculations of Indirect Nuclear Spin-Spin Coupling Constants 1J(31P, 13C) in λ3-Phosphaalkynes

2003 ◽  
Vol 58 (11) ◽  
pp. 1041-1044 ◽  
Author(s):  
Bernd Wrackmeyer
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Strong Dependence ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Positive Sign ◽  
Spin Orbital ◽  
Functional Theory ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The calculation of the spin-spin coupling constants 1J(31P,≡13C) of λ3-1-phosphaalkynes P≡C-R (R = H, Me, tBu, Ph, SiMe3 and NMe2) using density functional theory (DFT) have revealed a positive sign of this coupling constant in agreement with the experiment for P≡C-tBu. The calculations have shown that the Fermi contact (FC) contribution to this coupling is negative [in contrast to FC for 1J(14N,≡13C) in the corresponding nitriles], and that the positive sign of 1J(31P,≡13C) is the result of significant contributions arising from spin-dipole (SD) and paramagnetic spin-orbital (PSO) terms. Coupling constants were also calculated for some representative λ3-phosphorus compounds containing two- and three-coordinate phosphorus, indicating the strong dependence of the FC term on the geometry at the phosphorus atom.

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.

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
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