Long-range proton-fluorine spin-spin coupling and 19F substituent chemical shifts (SCS) in the naphthalene ring system

1971 ◽  
Vol 24 (9) ◽  
pp. 1829 ◽  
Author(s):  
W Adcock ◽  
DG Matthews ◽  
SQA Rizvi
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Naphthalene Ring ◽  
Methyl Proton ◽  
Direct Mechanism ◽  
Spin Coupling Constants ◽  
Proton Resonances ◽  
Spin Spin Coupling

A number of acetyl-substituted fluoronaphthalenes have been synthesized and their fluorine as well as proton N.M.R. spectra have been measured. The methyl proton resonances of these derivatives appeared as a doublet which indicated long-range coupling with the fluorine. It was observed that the coupling (JMe,F) for 3-acetyl-2-fluoronaphthalene and o- fluoroacetophenone is independent of the magnitude of the 19F substituent chemical shifts (scs) which are shown to be sensitive indices of the bond-order differences in naphthalene (C 1 and C 2; C 2 and C 3) and benzene. Furthermore, the magnitude of the long-range proton-fluorine spin-spin coupling constants are solvent dependent. The data are clearly in accord with a predominant contribution of a ?direct? mechanism to the proton-fluorine 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.

C—H … O=C and C—H … H—C interactions in the side chains of 2-isopropylbenzaldehyde. A negative 5J(CHO,CH(CH3)2)

1991 ◽  
Vol 69 (6) ◽  
pp. 919-926 ◽  
Author(s):  
Ted Schaefer ◽  
Kerry J. Cox
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Aldehyde Group ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Side Chain ◽  
Side Chains ◽  
Hydrogen Atoms ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

The 1H nuclear magnetic resonance spectra of 2-isopropylbenzaldehyde in CS2/C6D12 and acetone-d6 solutions provide the chemical shifts and coupling constants of all the protons. The long-range coupling constants involving the side-chain protons yield certain sums of the populations of the four putatively planar conformations. The o-anti conformers have a fractional population of 0.55(3) in the polar and of 0.49(3) in the nonpolar solvent. The conformers in which the methine C—H bond lies cis to the aldehyde group have a fractional population of 0.83(3) in both solutions. The close approach of the methine and aldehydic hydrogen atoms in one conformer is indicated by a negative proximate coupling constant between their protons of –0.39(1) Hz. The chemical shifts of the ring and of the side-chain protons are consistent with the conformer populations deduced from the long-range coupling constants and also with the indications that the side chains do not, on average, deviate from "coplanarity" with the ring by much more or less than in the parent compounds. The C—H … H—C and C—H … O=C interactions in the o-syn and o-anti conformers are most likely repulsive and of very similar magnitude and lead to a significant deshielding of the protons in these moieties. Molecular orbital computations are also reported and are an aid in estimating the populations of the individual conformers. The STO-3G MO structures have H … H and H … O distances well below the sums of the van der Waals radii of hydrogen and oxygen atoms in the conformers with the methine C—H bond placed cis to the aldehyde group, yet these are computed to be by far the most abundant by the STO-3G as well as by AM1 algorithms. Key words: 2-isopropylbenzaldehyde, conformations of; 2-isopropylbenzaldehyde, proximate spin–spin coupling constants in; MO calculations, STO-3G, and AM1 on 2-isopropylbenzaldehyde, 1H NMR and long-range spin–spin coupling constants in 2-isopropylbenzaldehyde.

scholarly journals A relationship between some long-range 2H/1H isotope shifts in 13C nuclear magnetic resonance and long-range spin–spin coupling constants for toluene, ethylbenzene, and isopropylbenzene

1983 ◽  
Vol 61 (12) ◽  
pp. 2777-2778 ◽  
Author(s):  
Ted Schaefer ◽  
James Peeling ◽  
Timothy A. Wildman
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Ring Plane ◽  
Expectation Value ◽  
Deuterium Substitution ◽  
13C Nuclear Magnetic Resonance ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

A very good correlation exists between long-range spin–spin coupling constants involving the α-protons in toluene, ethylbenzene, and cumene, and the changes in the chemical shifts of the para and α carbons caused by deuterium substitution at the α carbon. The coupling constants depend on sin2 θ, where θ is the angle by which the α C—H bond twists out of the ring plane, and can be used to find the expectation value of sin2 θ. Consequently the observed correlation provides quantitative support for the hyperconjugative model employed by Wesener and Günther.

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...

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.

The planar conformation of 2-methylthiobenzaldehyde in solution

1983 ◽  
Vol 61 (1) ◽  
pp. 26-28
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spectral Parameters ◽  
H Nmr ◽  
Heavy Atoms ◽  
Planar Conformation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Infrared Data

The 1H nmr spectral parameters are extracted for a 4 mol% solution of 2-methylthiobenzaldehyde in CCl4 at 305 K. The long-range spin–spin coupling constants involving the aldehydic and methyl protons are consistent only with a preferred conformation in which all heavy atoms are coplanar, as are the chemical shifts of the ring and methyl protons. This conclusion contradicts previous interpretations of the dipole moment, the nmr parameters, and of the infrared data for CCl4 solutions. The present data show that the O-syn and O-anti forms of the compound are present in roughly equal proportions.

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