The conformational dependence of in some 4-fluorophenyl derivatives of methane, ethene, and cyclohexane

1985 ◽  
Vol 63 (1) ◽  
pp. 24-29 ◽  
Author(s):  
Ted Schaefer ◽  
James Peeling ◽  
Glenn H. Penner ◽  
Alberta Lemire ◽  
Rudy Sebastian
Keyword(s):  
Carbon Atom ◽  
Spin Coupling ◽  
Carbon Nucleus ◽  
Ring Plane ◽  
Electron Coupling ◽  
Planar Form ◽  
Conformational Preferences ◽  
Vinyl Group ◽  
Spin Spin Coupling ◽  
Derivatives Of

The spin–spin coupling over six bonds between 19F and 13C nuclei on the sidechain in thirteen 4-fluorophenyl derivatives appears to be mediated by a σ–π mechanism. Its magnitude depends somewhat on the hybridization state of the carbon atom carrying the coupled nucleus, as well as on the electronegativity of substituents attached to this carbon atom. A consistent behaviour of this coupling is observed if its value is assumed to be proportional to sin2 θ, where θ is the angle by which the bond carrying the coupled carbon nucleus twists out of the ring plane. However, in 4-fluorostyrene [Formula: see text] is a π electron coupling in the planar form, so that its magnitude decreases as the vinyl group twists out of the benzene plane. The σ–π contribution to this coupling is smaller than the π component. [Formula: see text] is used to assess the conformational preferences of a number of compounds, including 4-fluoro-α-methylstyrene, 4,4′-difluorodiphenylmethane, 1,1-dichloro-2,2-bis(4-fluorophenyl)ethane, and 1-(4-fluorophenyl)-N-methylcyclohexylamine.

scholarly journals Concerning in 2-methylphenol and its derivatives. A proximate coupling

1985 ◽  
Vol 63 (3) ◽  
pp. 773-776 ◽  
Author(s):  
Ted Schaefer ◽  
Timothy A. Wildman ◽  
Rudy Sebastian
Keyword(s):  
Spin Coupling ◽  
Hydroxyl Group ◽  
Methyl Group ◽  
Proximate Mechanism ◽  
Tert Butyl ◽  
Vinyl Group ◽  
Spin Spin Coupling ◽  
Derivatives Of

In 2-chloro-6-methylphenol in CCl4 solution, [Formula: see text] the spin–spin coupling between the hydroxyl and methyl protons, is + 68(3) mHz. In this compound, the hydroxyl group lies trans to the methyl group. If the coupling becomes −120 ± 60 mHz in a cis orientation of these two groups, then the apparent vanishing of [Formula: see text] in some derivatives of 2-methylphenol is understandable, as well as its presence in other derivatives. Computations of this coupling imply its proximate mechanism and can rationalize its value of −220 ± 20 mHz in 2-tert-butyl-6-methylphenol. Analogies are noted with [Formula: see text] in 2-trifluoromethyl phenol and with a coupling in styrene, which also appears to vanish in certain orientations of the vinyl group.

Proton spin–spin coupling constants and intramolecular hydrogen bonding in bromine derivatives of 1,3-dihydroxybenzene

1976 ◽  
Vol 54 (14) ◽  
pp. 2228-2230 ◽  
Author(s):  
Ted Schaefer ◽  
J. Brian Rowbotham
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Groups ◽  
Oh Groups ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of

The conformational preferences in CCl4 solution at 32 °C of the hydroxyl groups in bromine derivatives of 1,3-dihydroxybenzene are deduced from the long-range spin–spin coupling constants between hydroxyl protons and ring protons over five bonds. Two hydroxyl groups hydrogen bond to the same bromine substituent in 2-bromo-1,3-dihydroxybenzene but prefer to hydrogen bond to different bromine substituents when available, as in 2,4-dibromo-1,3-dihydroxybenzene. When the OH groups can each choose between two ortho bromine atoms, as in 2,4,6-tribromoresorcinol, they apparently do so in a very nearly statistical manner except that they avoid hydrogen bonding to the common bromine atom.

The proximate spin–spin coupling, 5J(F,CH3), as a quantitative conformational indicator in alkylfluorobenzenes and related compounds

1986 ◽  
Vol 64 (8) ◽  
pp. 1602-1606 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Glenn H. Penner ◽  
S. R. Salman
Keyword(s):  
Nuclear Spin ◽  
Spin Coupling ◽  
Torsional Angle ◽  
Rotational Behaviour ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Spin Spin Coupling ◽  
Torsional Potentials ◽  
Derivatives Of ◽  
Related Compounds

The through-space or proximate nuclear spin–spin coupling constant, 5J(F,CH3) = 5J, between methyl protons and ring fluorine nuclei in alkylfluorobenzenes is postulated as [Formula: see text] θ being the torsional angle for the [Formula: see text] bond. A and B are obtained from the known internal rotational behaviour in 2,6-difluoroethylbenzene and the corresponding cumene derivative. The parameterization is tested on the observed 5J in derivatives of 2,4,6-tri-tert-butyl- and 2,4,6-tri-isopropyl-fluorobenzene, in 2-chloro-6-fluoroisopropylbenzene, 2,6-difluoro-α-methylstyrene, and N-methyl-8-fluoroquinolinium halides. A prediction is made for 5J in 2,6-difluoro-tert-butylbenzene. It appears that the present parameterization allows the derivation of approximate torsional potentials from proximate couplings, for example in α,α-dimethyl-2,6-difluorobenzyl alcohol.

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.

scholarly journals One and Multiple Bonds Interatomic Spin-Spin Coupling inη6-Cymene Ru(II) of 3,5-Dimethyl-, 3,5-Dicarboxylic-, and 5-Phenyl-pyrazole Derivatives

2015 ◽  
Vol 2015 ◽  
pp. 1-11
Author(s):  
Adebayo A. Adeniyi ◽  
Peter A. Ajibade
Keyword(s):  
Ruthenium Complexes ◽  
Spin Coupling ◽  
Multiple Bonds ◽  
Interatomic Distances ◽  
Spin Interactions ◽  
Fermi Contact ◽  
Shielding Tensor ◽  
Spin Spin Coupling ◽  
Hydrolysis Of ◽  
Derivatives Of

The changes in the interatomic distances and the corresponding spin-spin coupling as a result of the hydrolysis of the ruthenium complexes and the effects of different derivatives of the pyrazole ligands and the substituents methyl, carboxylic, and phenyl on the pyrazole rings were studied. A good agreement was obtained between the experimental and the theoretical proton NMR. Significant changes are observed in the isotropic and anisotropic shielding tensor of the atoms and related spin-spin coupling of their bonds due to hydrolysis of the complexes. This observation gives more insight into the known mechanism of activation of the ruthenium complexes by hydrolysis. There are no direct effects of interatomic distances on many of the computed spin-spin couplings with the exception of1J(Ru-N) which shows significant changes especially within the pair of1J(Ru-N) in the complexes with two nitrogen atoms of the bis-pyrazole moiety. The magnitude of interatomic spin-spin coupling of the Ru-X follows the order of Ru-Cl > Ru-N > Ru-C > Ru-O. The Ramsey term Fermi contact (FC) has the most significant contribution in most of the computed spin-spin interactions except in1J(Ru-Cl) and1J(N-N⁎) which are predominantly defined by the contribution from the paramagnetic spin orbit (PSO).

A proton magnetic resonance determination of the small rotational barriers about the C—Si bond in phenyl derivatives of chloro and methyl silanes

1977 ◽  
Vol 55 (3) ◽  
pp. 557-561 ◽  
Author(s):  
William J. E. Parr ◽  
Ted Schaefer
Keyword(s):  
Magnetic Resonance ◽  
Proton Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of ◽  
Low Energy Conformations

The long-range spin–spin coupling constants between protons bonded to silicon and ring protons in C6H5SiH3, C6H5SiH2Cl, C6H5SiH2CH3, C6H5SiHCl2, and C6H5SiH(CH3)2 are determined from the proton magnetic resonance spectra of benzene solutions. A hindered rotor treatment of the barrier to internal rotation about the C—Si bond, in conjunction with the coupling constants over six bonds, allows the deduction of the low-energy conformations for C6H5SiH(CH3)2 and for C6H5SiHCl2, as well as of barriers of 1.0 ± 0.2 kcal/mol. The approach becomes less reliable for C6H5SiH2CH3 and for C6H5SiH2Cl and, particularly for the latter compound, the derived barrier is very likely an upper limit only. Ab initio molecular orbital calculations of the conformational energies are reported for C6H5SiH3, C6H5SiH2Cl, and for C6H5SiHCl2.

scholarly journals The conformational behaviour of 5Jm(F,CH) in 3,5-difluoro derivatives of toluene, ethylbenzene, and cumene. Applications

1988 ◽  
Vol 66 (6) ◽  
pp. 1490-1494 ◽  
Author(s):  
Ted Schaefer ◽  
Craig S. Takeuchi ◽  
Steven Eric Sveinson
Keyword(s):  
Large Degree ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Derivatives Of

The CNDO/2 and INDO MO FPT values for 5Jm(F,CH3) in 3-fluoro- and 3,5-difluorotoluene are exactly reproduced by A cos2 θ + B sin2 θ + C sin2 (θ/2). Here θ is the angle by which the α C—H bond twists out of the benzene plane. Adjustment of A,B, and C to give an agreement with experiment for 3,5-difluorotoluene yields an equation, best considered empirical, which is tested by 5J(F,CH) in 3,5-difluoroethylbenzene and 3,5-difluoroisopropylbenzene. The equation reproduces 5J(F,CH) in these two compounds, the values of [Formula: see text] being derived from 6Jp(H,CH), the spin–spin coupling constants over six bonds between the α and para ring protons. 5J(F,CH) is obtained for the asymmetrical compounds, 2,3-difluorobenzylidene diacetate and 2-bromo-5-fluorobenzylidene diacetate. It is shown how 5J(F,CH) in the latter can discriminate between two conformers, each of which, on the basis of 6J(H,CH), will be characterized by a large degree of torsion about the [Formula: see text] bond.

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