The conformational behaviour of 2-fluoro and of 2,6-difluoroacetophenone implied by proximate spin–spin coupling constants and MO calculations

1985 ◽  
Vol 63 (8) ◽  
pp. 2256-2260 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner ◽  
Timothy A. Wildman ◽  
James Peeling
Keyword(s):  
Temperature Dependence ◽  
Geometry Optimization ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Population Distributions ◽  
Carbon Carbon Bond ◽  
Acetyl Group ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The temperature dependence of [Formula: see text], the nuclear spin–spin coupling constant over five formal bonds between the methyl protons and the 19F nucleus in 2-fluoroacetophenone and 2,6-difluoroacetophenone, is modelled on the assumption that 5J is a proximate coupling and that the STO 3G MO potential functions describe the population distributions of the rotamers defined by rotation about the exocyclic sp2–sp2 carbon–carbon bond. It is assumed that 5J has a cos4 θ dependence between 0 and 90°, where θ is the angle by which the acetyl group twists out of the plane of the benzene plane. The potential function is obtained from extensive geometry optimization procedures for a range of θ values. At 305 K, nonplanar conformations are substantially populated in 2-fluoroacetophenone, according to this model, which is also consistent with the idea that the 2,6-difluoro derivative has a markedly nonplanar ground state. The model reproduces the large 5J in the monofluoro relative to the difluoro compound, as well as the much larger temperature dependence in the former.

An estimate of the spin–spin coupling constant, 1J(1H,13C), in gaseous benzene

1996 ◽  
Vol 74 (8) ◽  
pp. 1524-1525 ◽  
Author(s):  
Ted Schaefer ◽  
Guy M. Bernard ◽  
Frank E. Hruska
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Dielectric Constant ◽  
Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Gaseous Benzene

An excellent linear correlation (r = 0.9999) exists between the spin–spin coupling constants 1J(1H,13C), in benzene dissolved in four solvents (R. Laatikainen et al. J. Am. Chem. Soc. 117, 11006 (1995)) and Ando's solvation dielectric function, ε/(ε – 1). The solvents are cyclohexane, carbon disulfide, pyridine, and acetone. 1J(1H,13C)for gaseous benzene is predicted to be 156.99(2) Hz at 300 K. Key words: spin–spin coupling constants, 1J(1H,13C) for benzene in the vapor phase; spin–spin coupling constants, solvent dielectric constant dependence of 1J(1H,13C) in benzene; benzene, estimate of 1J(1H,13C) in the vapor; nuclear magnetic resonance, estimate of 1J(1H,13C) in gaseous benzene.

Signs of spin–spin coupling constants between aldehydic and ring protons in 2,6-dinitrobenzaldehyde. Evidence for a hyperconjugative contribution to JpH,CHO

1969 ◽  
Vol 47 (19) ◽  
pp. 3529-3533 ◽  
Author(s):  
C. L. Bell ◽  
S. S. Danyluk ◽  
T. Schaefer
Keyword(s):  
Aldehyde Group ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Para Position ◽  
Steric Interaction ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The spin–spin coupling constant between the aldehydic proton and the proton in the para position, JpH,HCO is negative in 2,6-dinitrobenzaldehyde. JpH,CHO is also very likely negative in 2,6-dichlorobenzaldehyde. It is suggested that steric interaction with the ortho substituents forces the aldehyde group out of a coplanar conformation and leads to an interaction of the aldehydic C–H bond with the π system of the ring. Tentative values of θ, a measure of the deviation from coplanarity, are given.

Anisotropy of indirect spin–spin coupling constants from nuclear magnetic resonance powder patterns of rigid solids. 1J(31P,199Hg) in [HgP(o-tolyl)3(NO3)2]2

1988 ◽  
Vol 66 (8) ◽  
pp. 1821-1823 ◽  
Author(s):  
Glenn H. Penner ◽  
William P. Power ◽  
Roderick E. Wasylishen
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constants ◽  
Fermi Contact ◽  
Spin Spin Coupling ◽  
Contact Mechanism ◽  
Nuclear Magnetic

The anisotropy of the indirect 31P,199Hg spin–spin coupling constant, ΔJ, in solid [HgP(o-tolyl)3(NO3)2]2 is obtained from an analysis of the 31P nuclear magnetic resonance powder pattern. The value of ΔJ, 5170 ± 250 Hz, is large and indicates that mechanisms other than the Fermi contact mechanism are important for this spin–spin coupling. The powder spectrum also indicates that the absolute sign of 1J(31P,199Hg) is positive.

Long-range 13C, 13C spin–spin coupling constants in anisole and some derivatives

1988 ◽  
Vol 66 (7) ◽  
pp. 1635-1640 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Methoxy Group ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Nuclear Magnetic

13C nuclear magnetic resonance chemical shifts and nJ(13C,13C) are reported for anisole and 16 of its derivatives, all enriched with 13C in the methoxyl group. 5J(13C,13C) is directly proportional to sin2θ, where θ is the angle by which the methoxy group twists about the C(1)—O bond. In acetone-d6 solution, 5J(C,C) is not observable for a number of 4-substituted anisoles, except for 1,4-dimethoxybenzene. For the latter, 5J(C,C) is compatible with a twofold barrier of 19.3 ± 1.1 kJ/mol hindering rotation about the C(1)—O bond. However, it is unlikely that the barrier is purely twofold in nature. The observed 5J(C,C) is also compatible with 10.5 and 6.0 kJ/mol for the twofold and fourfold components, respectively, implying a dynamical nuclear magnetic resonance barrier of less than 13 kJ/mol. While phase and solvent effects on the internal barrier in anisole are certainly substantial, it appears that a fourfold component must also be present. The apparent twofold barrier in 2,6-difluoroanisole is 5.4 ± 0.9 kJ/mol, based on 5J(C,C) and 6J(H-4,13C). The latter coupling constant is also reported for 1,2,3-trimethoxybenzene and used to deduce its conformation. The θ dependence of 3J(C,C) and 4J(C,C) is briefly discussed for symmetrical anisole derivatives. Differential 13C, 13C isotope shifts are reported for 1,4-dimethoxybenzene.

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.

Indirect Nuclear Spin-Spin Coupling Constants 1J(17O,13C) in Derivatives of Carbon Dioxide and Carbon Monoxide – Density Functional Theory (DFT) Calculations

2004 ◽  
Vol 59 (3) ◽  
pp. 286-290 ◽  
Author(s):  
Bernd Wrackmeyer
Keyword(s):  
Carbon Dioxide ◽  
Density Functional Theory ◽  
Carbon Monoxide ◽  
Density Functional ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Functional Theory ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Calculations of spin-spin coupling constants 1J(17O,13C) in carbon dioxide (1) carbon monoxide (2) and several derivatives using density functional theory (DFT) have been carried out. This coupling constant possesses a positive sign [reduced coupling constant 1K(17O,13C)<0] except for the parent acylium cation [H-CO]+ (4a). It is shown that the Fermi contact term (FC) is positive [< 0 for 1K(17O,13C)] and that there are significant contributions from spin-dipole (SD) and paramagnetic spin-orbital (PSO) interactions

The structure and internal rotational barrier of 3-phenyl-1-propyne by molecular orbital calculations and the J method

1987 ◽  
Vol 65 (7) ◽  
pp. 1496-1498 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Geometry Optimization ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Molecular Orbital Calculations ◽  
Three Solutions ◽  
Spectral Parameters ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The 1H nuclear magnetic resonance spectral parameters are reported for 3-phenyl-1-propyne dissolved in CCl4, C6D6, and in acetone-d6. The long-range spin–spin coupling constants imply very small and perhaps vanishing barriers to internal rotation about the [Formula: see text] bond in all three solutions, in contrast to benzyl cyanide in which there exist significant solvent perturbations of the internal barrier. STO 3G MO computations, utilizing geometry optimization procedures, imply an internal rotational potential of V/kJ mol−1 = −2.8 sin2 ψ − 0.6 sin2 2ψ; the angle ψ is 90° when the C≡C bond lies in a plane perpendicular to the benzene plane. 6-31G MO energies imply V/kJ mol−1 = −0.3 sin2 ψ − 0.4 sin2 2ψ, the fourfold component being larger than the twofold. A flat minimum occurs near ψ = 50°.

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