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.

The Geometrical Dependence of Experimental and Theoretical Nuclear Spin–Spin Coupling Constants in the 15NH2 Fragment

1973 ◽  
Vol 51 (18) ◽  
pp. 3087-3096 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
T. Schaefer
Keyword(s):  
Benzene Ring ◽  
Nuclear Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Amino Group ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Spin Coupling Constants ◽  
Experimental Values ◽  
Spin Spin Coupling

Approximate molecular orbital theory at the INDO level of approximation has been used to examine 1J(15N,H) and 2(HNH) in ammonia as a function of the HNH angle. The couplings are very sensitive to the value of the HNH angle in the range from 110 to 120°. The computed trends are compared with those observed in other compounds containing the 15NH2 fragment. The signs and magnitudes of 1J(15N,H) and 2J(HNH) have been measured for 2-aminoacetophenone at temperatures where the amino protons are nonequivalent. The observed and calculated results suggest that the amino group lies in the plane of the benzene ring. In aniline the magnitude of 2J(HNH) lies between 1 and 2 Hz and on the basis of the trends in the calculated and experimental values the sign can be confidently taken as negative.

An increased internal rotational barrier in thiophenol caused by meta substituents

1985 ◽  
Vol 63 (9) ◽  
pp. 2471-2475 ◽  
Author(s):  
Ted Schaefer ◽  
James D. Baleja ◽  
Glenn H. Penner
Keyword(s):  
Molecular Orbital ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Theory ◽  
Mo Calculations ◽  
Orbital Theory ◽  
Spin Coupling Constants ◽  
Internal Barriers ◽  
Spin Spin Coupling

The twofold internal barriers to rotation about the C—S bond in 3,5-diX-thiophenols were determined in solution from long-range spin–spin coupling constants. They are 3.4, 4.85, 5.3, 6.45, and 7.25 ± 10% kJ/mol for X = H, CH3, OCH3, F, and Cl, respectively. In 3,5-dichloro-4-hydroxythiophenol, V2 is −0.8 kJ/mol as compared to −1.9 kJ/mol in 4-methoxythiophenol. The para substituent here dominates. The observed barriers are in rough agreement with arguments based on perturbation molecular orbital theory and with MO calculations of changes in the barrier caused by substituents. The computed values appear as nearly pure twofold barriers with very small fourfold components.

Valence bond calculation of nuclear spin-spin coupling constants. 2. Coupled valence bond perturbation theory

1979 ◽  
Vol 83 (11) ◽  
pp. 1470-1472 ◽  
Author(s):  
Bernard. Kirtman ◽  
Kathryn Barr. Kirtley
Keyword(s):  
Perturbation Theory ◽  
Nuclear Spin ◽  
Valence Bond ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

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.

Molecular orbital theory of nuclear spin coupling constants

1964 ◽  
Vol 8 (1) ◽  
pp. 1-18 ◽  
Author(s):  
J.A. Pople ◽  
D.P. Santry
Keyword(s):  
Molecular Orbital ◽  
Nuclear Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Spin Coupling Constants

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.

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