Proton Spin–Spin Coupling Constants in Isothiazole, Isoxazole, and some of their Alkyl Derivatives

1974 ◽  
Vol 52 (5) ◽  
pp. 833-837 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
J. Brian Rowbotham ◽  
Ted Schaefer
Keyword(s):  
Chemical Shifts ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Common Mechanism ◽  
Orbital Theory ◽  
Alkyl Derivatives ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms

The signs and magnitudes of the spin–spin coupling constants over three to six bonds between protons in isothiazole, isoxazole, and in 10 of their alkyl derivatives are measured and discussed in terms of the coupling mechanisms. The chemical shifts of ring protons and methyl protons appear to arise from a common mechanism originating in the ring but are not simply related to electron densities calculated by molecular orbital theory at the CNDO/2 level of approximation.

ChemInform Abstract: PROTON SPIN-SPIN COUPLING CONSTANTS IN ISOTHIAZOLE, ISOXAZOLE, AND SOME OF THEIR ALKYL DERIVATIVES

1974 ◽  
Vol 5 (22) ◽  
Author(s):  
RODERICK E. WASYLISHEN ◽  
J. BRIAN ROWBOTHAM ◽  
TED SCHAEFER
Keyword(s):  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Alkyl Derivatives ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

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.

Unexpected signs of five-bond and six-bond proton spin–spin coupling constants in some acyclic conjugated systems. Through-space couplings.

1976 ◽  
Vol 54 (14) ◽  
pp. 2235-2242 ◽  
Author(s):  
Ted Schaefer ◽  
Hyman D. Gesser ◽  
J. Brian Rowbotham
Keyword(s):  
Vinyl Ether ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Methyl Vinyl ◽  
Spin Coupling Constants ◽  
Sign Sequence ◽  
Methyl Vinyl Ether ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms

The signs and magnitudes of spin–spin coupling constants over five and/or six bonds in some N-methyl and N,N-dimethyl hydrazones, in methyl vinyl ether, 4-methoxy-3-butene-2-one, 1-methoxy-1,3-butadiene, 1-butene, and in anisole are discussed in terms of coupling mechanisms. In the hydrazones the five-bond couplings between methyl and olefinic protons are negative, while six-bond couplings between protons in methyl groups are positive, a reversal of the expected sign sequence. INDO-MO-FPT calculations are not in agreement with observation, but the disagreement may be a consequence of faulty structural assumptions. The sizeable six-bond couplings imply a negative σ–π contribution to the five-bond constants. The calculated and observed negative couplings over five bonds in methyl vinyl ether and the other molecules above emphasize their dependence on the proximity of the bonds containing the coupled nuclei and are reliable indicators of bond arrangements in these molecules.

Nuclear magnetic resonance study of carbethoxypyrroles

1970 ◽  
Vol 48 (14) ◽  
pp. 2303-2305 ◽  
Author(s):  
M. W. Roomi ◽  
H. Dugas
Keyword(s):  
Chemical Shifts ◽  
Nuclear Magnetic Resonance Study ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ring Proton ◽  
Proton Coupling ◽  
Low Field ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The chemical shifts and the ring proton coupling constants of various substituted carbethoxypyrroles are reported.The electron-withdrawing effect of the carbethoxy groups shifts the resonances of the ring substituents to low field while the inductive and mesomeric effects of the methyl groups shift the resonances to higher field. The deshielding effect is more pronounced with 2-carbethoxypyrroles than for 3-carbethoxypyrroles. The ring proton spin–spin coupling constants depend on the nature of substituents and increase with the electronegativity of the substituents. In some cases long-range coupling between the methyl side-chain protons and ring protons could be observed.

Experimental and Theoretical Estimates of Sigma and Pi Electron Contributions to Long-range Spin–Spin Coupling Constants in Coumarin and its Methyl Derivatives

1973 ◽  
Vol 51 (6) ◽  
pp. 953-960 ◽  
Author(s):  
J. B. Rowbotham ◽  
T. Schaefer
Keyword(s):  
Valence Bond ◽  
Electron System ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Orbital Theory ◽  
Coupling Path ◽  
Spin Coupling Constants ◽  
Methyl Derivatives ◽  
Spin Spin Coupling

A full analysis of the p.m.r. spectra of coumarin and five of its methyl derivatives allows the assignment of σ and π electron components to the inter-ring proton–proton spin–spin coupling constants. Magnitudes of up to 0.3 Hz are observed over a coupling path of eight bonds. The σ and π components can be combined on the basis of the appropriate valence bond structures to predict closely the observed parameters in naphthalene, suggesting only weak participation of the ether oxygen atom in the π electron system of coumarin. Calculations of the inter-ring coupling constants at the INDO and CNDO/2 levels of molecular orbital theory are helpful in the interpretation of the observed data, the agreement with experiment being quantitative in many instances. Comparison of the observed coupling constants in coumarin and styrene with the INDO results for an assumed planar form of the latter suggests that styrene exists in a nonplanar conformation.

scholarly journals Glycosaminoglycan Monosaccharide Blocks Analysis by Quantum Mechanics, Molecular Dynamics, and Nuclear Magnetic Resonance

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Sergey A. Samsonov ◽  
Stephan Theisgen ◽  
Thomas Riemer ◽  
Daniel Huster ◽  
M. Teresa Pisabarro
Keyword(s):  
Molecular Dynamics ◽  
Dihedral Angle ◽  
Chemical Shifts ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Proton Proton ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
The Impact

Glycosaminoglycans (GAGs) play an important role in many biological processes in the extracellular matrix. In a theoretical approach, structures of monosaccharide building blocks of natural GAGs and their sulfated derivatives were optimized by a B3LYP6311ppdd//B3LYP/6-31+G(d) method. The dependence of the observed conformational properties on the applied methodology is described. NMR chemical shifts and proton-proton spin-spin coupling constants were calculated using the GIAO approach and analyzed in terms of the method's accuracy and sensitivity towards the influence of sulfation, O1-methylation, conformations of sugar ring, andωdihedral angle. The net sulfation of the monosaccharides was found to be correlated with the1H chemical shifts in the methyl group of the N-acetylated saccharides both theoretically and experimentally. Theωdihedral angle conformation populations of free monosaccharides and monosaccharide blocks within polymeric GAG molecules were calculated by a molecular dynamics approach using the GLYCAM06 force field and compared with the available NMR and quantum mechanical data. Qualitative trends for the impact of sulfation and ring conformation on the chemical shifts and proton-proton spin-spin coupling constants were obtained and discussed in terms of the potential and limitations of the computational methodology used to be complementary to NMR experiments and to assist in experimental data assignment.

Carbon-13, proton spin–spin coupling constants in some 4-substituted isothiazoles and related heterocyclics

1977 ◽  
Vol 55 (4) ◽  
pp. 619-624 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Harold M. Hutton
Keyword(s):  
Perturbation Theory ◽  
Nuclear Spin ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Spin Coupling Constants ◽  
Semi Empirical ◽  
Spin Spin Coupling

Carbon-13, proton nuclear spin–spin coupling constants have been measured for a number of 4-substituted isothiazoles. The observed values are compared with those measured in other heterocyclic systems and those calculated in the parent and related heterocyclics using finite perturbation theory and semi-empirical molecular orbital theory at the CNDO/2 and INDO levels of approximation.

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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