Long-range proton–19F spin–spin coupling interactions in phenyltrifluorosilane

1977 ◽  
Vol 55 (18) ◽  
pp. 3243-3247 ◽  
Author(s):  
William J. E. Parr ◽  
T. Schaefer ◽  
K. Marat
Keyword(s):  
Long Range ◽  
Resonance Spectrum ◽  
Base Point ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hindered Rotation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms

Analysis of the proton magnetic resonance spectrum of phenyltrifluorosilane yields the spin–spin coupling constants between the fluorine nuclei and the protons. These are compared with the analogous long-range coupling constants in benzotrifluoride, toluene, and phenylsilane and are rationalized in terms of coupling mechanisms. The coupling over six bonds is assessed as a base point for the estimation of hindered rotation about the carbon–silicon bond.

Conformational dependence of long-range spin-spin coupling constants in 2,6-dichlorobenzylfluoride

1969 ◽  
Vol 47 (19) ◽  
pp. 3688-3690 ◽  
Author(s):  
T. Schaefer ◽  
C. M. Wong ◽  
K. C. Tam
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Double Resonance ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Double resonance experiments on the proton magnetic resonance spectrum of 2,6-dichlorobenzylfluoride yield the signs of the long-range coupling constants between the ring protons and the fluorine nuclei and protons in the fluoromethyl group. The signs and magnitudes of the long-range couplings are discussed in terms of their dependence on the conformation of the fluoromethyl group.

scholarly journals Proton Magnetic Resonance Spectrum of 1-Penten-3-yne. INDO and CNDO/2 Molecular Orbital Calculations on Long-Range Spin–Spin Coupling Constants in Enynes

1972 ◽  
Vol 50 (12) ◽  
pp. 1863-1867 ◽  
Author(s):  
L. Ernst ◽  
H. M. Hutton ◽  
T. Schaefer
Keyword(s):  
Molecular Orbital ◽  
Long Range ◽  
Benzene Solution ◽  
Parent Compound ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The high resolution p.m.r. spectra of 1-penten-3-yne in carbon disulfide and in benzene solution are analyzed. Long-range spin–spin coupling constants are discussed in terms of σ and π electron contributions. Comparisons are made with the isomeric 2-methyl-1-buten-3-yne and the parent compound, vinylacetylene. The results of INDO and CNDO/2 molecular orbital calculations are compared to the experimental coupling constants. It is concluded that the π electron contribution to 5J in enyne systems is +0.6 to 0.7 Hz and that σ electron contributions are rather small, the transoid ("pseudo-zig–zag") being larger than the cisoid one. Observed allylic coupling constants in the propene derivative are compared with the calculated values, including those for propene and 2-cyanopropene, available in the literature.

The mechanisms of long-range 13C,19F and 19F,19F coupling constants in derivatives of biphenyl and fluorene. Differential isotope shifts

1986 ◽  
Vol 64 (11) ◽  
pp. 2162-2167 ◽  
Author(s):  
Ted Schaefer ◽  
James Peeling ◽  
Glenn H. Penner
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Diffraction Patterns ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms ◽  
Coupling Components

13C,19F and 19F,19F nuclear spin–spin coupling constants over n formal bonds, n = 1–9, are reported for 4-fluorobiphenyl, 4,4′-difluorobiphenyl, 4,4′-difluoro-2,2′,6,6′-tetramethylbiphenyl, 2,7-difluorofluorene, 2-fluoro-9-fluorenone, and 2,7-difluoro-9-fluorenone in acetone solutions. The signs of many of the coupling constants are deduced from second-order spectral phenomena caused by differential 13C isotope effects on the I9F nmr chemical shifts. Theoretical potentials, based on geometry-optimized STO 3G MO computations for 4-fluorobiphenyl and 4,4′-difluorobiphenyl, yield expectation values for the torsion angles about the exocyclic C—C linkage that are very close to those deduced from electron diffraction patterns. These potentials and INDO MO FPT computations of the long-range coupling constants allow a discussion of the coupling mechanisms. In Hz, 9J(F,F) = 1.3(1) cos2 θ, where θ is zero for a planar biphenyl, while 8J(C,F) = 0.8(1) cos2 θ and 7J(C,F) = −0.43(5) cos2 θ. 6J(C,F) is a composite of σ–π and π electron coupling components and is written in Hz as 0.57(1) + 0.29(1) sin2 θ. The corresponding coupling constants in the fluorene and 9-fluorenone derivatives are enhanced in magnitude relative to a hypothetical planar biphenyl derivative. It is tentatively suggested that 5J(C,F) consists of three coupling components, one negative and proportional to cos2 θ, the other two positive and independent of θ. 4J(C,F) is suggested to consist of a σ component of −1.0 Hz and a π component proportional to the atom–atom polarizability for the parent hydrocarbon.

Long-range spin–spin coupling constants between ring protons and aldehydic protons in some para-substituted benzaldehydes

1969 ◽  
Vol 47 (21) ◽  
pp. 4005-4010 ◽  
Author(s):  
S. S. Danyluk ◽  
C. L. Bell ◽  
T. Schaefer
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Proton Proton ◽  
Proton Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms ◽  
Benzaldehyde Derivatives

The long-range proton–proton coupling constants between the ring protons and the aldehydic proton are reported for a series of para-substituted benzaldehyde derivatives. It was found that JoH,CHO < 0 and JmH,CHO > 0. Furthermore, JoH,CHO increases in magnitude as the electron donating power of the sub-stituent increases. A similar trend is observed forJmH,CHO but the ratio of the increase to the magnitude of JmH,CHO is much less than for JoH,CHO. A good correlation is obtained between JoH,CHO and the sub-stituent parameters of Swain and Lupton.The coupling constant data are discussed in terms of σ and π coupling mechanisms and it is concluded that σ electron mechanisms are dominant for both JoH,CHO and JmH,CHO.

scholarly journals Signs of proton–proton and proton–fluorine spin–spin coupling constants in 2-fluoro-3-methylpyridine. Sigma and pi contributions to coupling in a nitrogen heterocycle

1969 ◽  
Vol 47 (9) ◽  
pp. 1507-1514 ◽  
Author(s):  
T. Schaefer ◽  
S. S. Danyluk ◽  
C. L. Bell
Keyword(s):  
Nitrogen Atom ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nitrogen Heterocycle ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Proton Proton ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The signs of all proton–proton and proton–fluorine spin–spin coupling constants in 2-fluoro-3-methylpyridine have been determined by double and triple resonance experiments. The signs of the longrange coupling constants, JH,CH3 and JF,CH3 are the same as in fluorotoluene derivatives. Their magnitudes are consistent with the assumption that the nitrogen atom primarily polarizes the σ bonds in the molecule, leaving the π contribution to the long-range coupling relatively unaffected.

A proton magnetie resonance and molecular orbital study of the conformational preferences of the vinylic fragment in some 2-vinylfurans and in 2-vinylthiophene

1976 ◽  
Vol 54 (20) ◽  
pp. 3216-3223 ◽  
Author(s):  
William J. E. Parr ◽  
Roderick E. Wasylishen ◽  
Ted Schaefer
Keyword(s):  
Molecular Orbital ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Orbital Theory ◽  
Molecular Orbital Study ◽  
Conformational Preferences ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The stereospecific spin–spin coupling constants over five bonds between the α-proton in the side chain and the protons in the heterocycle in 2-vinylfuran, in its β-nitro and β-aldehydic derivatives, and in 2-vinylthiophene are used to demonstrate the preponderance of the s-trans conformers in polar and nonpolar solutions. These conclusions are compared with predictions made by molecular orbital theory at the STO-3G, INDO, CNDO/2, and MINDO/3 levels. Long-range coupling constants between the protons in the side chain and protons in the heterocycle are calculated by CNDO/2 and INDO–MO–FPT and are compared with experiment. It is concluded that the five-bond couplings involving the α-proton are most sensitive to conformation and that they are transmitted mainly via a σ electron mechanism. The other long-range coupling constants are discussed in terms of σ and π electron mechanisms. The STO-3G calculations yield barriers to internal rotation of greater than 4.8 kcal/mol.

The effects of substituents on the5J long-range spin-spin coupling constants in substituted benzaldehydes

1979 ◽  
Vol 12 (9) ◽  
pp. 542-543 ◽  
Author(s):  
R. H. Contreras ◽  
D. G. de Kowalewski ◽  
A. Osella
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Substituted Benzaldehydes ◽  
Spin Spin Coupling
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