Signs of long-range proton–fluorine spin–spin coupling constants in 2-amino-5-bromobenzotrifluoride

1968 ◽  
Vol 46 (4) ◽  
pp. 652-654 ◽  
Author(s):  
D. J. Blears ◽  
S. S. Danyluk ◽  
T. Schaefer
Keyword(s):  
Long Range ◽  
Bond Order ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Trifluoromethyl Group ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The signs of the spin–spin coupling constants between the fluorine nuclei in the trifluoromethyl group and the ring protons in 2-amino-5-bromobenzotrifluoride are reported. [Formula: see text] and [Formula: see text] are negative while [Formula: see text] is positive. These signs are in agreement with fluorine contact shifts in certain Ni(II) chelates and therefore provide evidence for hyperconjugation of the CF3 group with the ring. The magnitude of [Formula: see text] is rather larger than expected on the basis of a relationship between the square of the bond order between the relevant ring carbons and the size of the coupling.

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.

Long-range spin–spin coupling constants as an indicator of conformational preferences in ethyl and trifluoroethyl vinyl ethers

1977 ◽  
Vol 55 (15) ◽  
pp. 2835-2838 ◽  
Author(s):  
Ted Schaefer ◽  
William J. E. Parr
Keyword(s):  
Vinyl Ether ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ethyl Vinyl Ether ◽  
Spectroscopic Techniques ◽  
Ethyl Vinyl ◽  
Conformational Preferences ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The observed and calculated, negative, long-range spin–spin coupling constants over five bonds between olefinic and methylene protons in ethyl vinyl ether and in 2,2,2-trifluoroethyl vinyl ether are consistent with predominant s-cis planar conformations. The five-bond couplings are sensitive to the proximity of the bonds containing the coupled nuclei and are unobservably small in 1-butene where the H,H distances are somewhat larger than in the ethers. The present results concur with the arguments based on other spectroscopic techniques.

Molecular orbital computations and 1H nuclear magnetic resonance measurements of the bending motion of xanthene in the gas and in solution

1990 ◽  
Vol 68 (9) ◽  
pp. 1548-1552 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Long Range ◽  
Solvent Mixture ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ambient Temperatures ◽  
Folding Angle ◽  
Analytical Functions ◽  
Planar Molecule ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

STO-3G and 4-31G MO computations are reported for a range of values of the folding angle in xanthene, the dihedral angle between the benzene planes. Unlike 9,10-dihydroanthracene but like dibenzo-p-dioxin, its "parent" molecules, the inversion or puckering potential for xanthene is calculated to be rather flat. The molecular energies between a folding angle of 180° (planar molecule) and 120° are reproduced by analytical functions of [Formula: see text], θ being the folding angle. The long-range spin–spin coupling constants between the methylene protons and the aromatic protons at 300 K are reported for xanthene dissolved in a CS2/C6D12 solvent mixture and in acetone-d6 solution. These conformationally sensitive coupling constants are consistent with the theoretical puckering potentials and therefore with substantial "butterfly" motion at ambient temperatures. The computed geometries of xanthene are also given and briefly discussed. Keywords: xanthene, MO computations on inversion; xanthene, long-range spin–spin coupling constants; xanthene, internal motion; xanthene, inversion potentials.

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