Long-range proton-fluorine spin-spin coupling. Further evidence for a 'direct' mechanism

1973 ◽  
Vol 26 (12) ◽  
pp. 2659 ◽  
Author(s):  
W Adcock ◽  
SQA Rizvi
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Variable Temperature ◽  
Strong Support ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
Direct Mechanism ◽  
Spin Spin Coupling

A variable temperature p.m.r. study of outho- and peri-acetyl substituted fluoro-naphthalenes (including o-fluoroacetophenone) has been carried out. Further, 1-fluoro- 8-methylnaphthalene (previously unknown) has been synthesized and its p.m.r. spectra has been measured at various temperatures. The data, together with 19F substituent chemical shifts (SCS) for ortho-substituted cyanofluoronaphthalenes, provide further strong support for a through-space coupling mechanism (JMe,F).

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.

Proton magnetic resonance spectra of some benzo[b]thiophens. An investigation of substituent effects in a heteroaromatic system

1968 ◽  
Vol 21 (7) ◽  
pp. 1853 ◽  
Author(s):  
B Caddy ◽  
M Martin-Smith ◽  
RK Norris ◽  
ST Reid ◽  
S Sternhell
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Spin Coupling ◽  
Heteroaromatic System ◽  
Spin Spin Coupling ◽  
Magnetic Resonance Spectra

N.m.r. data for 19 5-substituted and 13 polysubstituted benzo[b]thiophens are tabulated. The influence of the substituents at C5 on the chemical shifts of H4 and H6 is discussed. Long-range interproton spin-spin coupling between H3 and H7, and between H2 and H6, is general in benzo[b]thiophens. The vicinal coupling J6,7 in 5-substituted benzo[b]thiophens varies directly and linearly with the electronegativity of the substituents at C5.

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.

Long-range spin-spin coupling in 1,4-benzoquinones and some related compounds

1966 ◽  
Vol 19 (4) ◽  
pp. 617 ◽  
Author(s):  
RK Norris ◽  
S Sternhell
Keyword(s):  
Long Range ◽  
Chemical Shifts ◽  
Point Of View ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Halogen Atoms ◽  
Methyl Methyl ◽  
Negative Coupling ◽  
Spin Spin Coupling ◽  
Related Compounds

N.m.r, data for fifteen 1,4-benzoquinones, four 1,4-naphthoquinones, and six cyclohex-2-ene-1,4-diones are tabulated. From these, and previously available data, it is possible to obtain characteristic ranges for methyl-allylic coupling constants (c 1.3 c/s) and methyl-methyl homoallylic coupling constants (c. 1.3 c/s) for this for this series of compounds as well as values for other long-range and vicinal interactions, including a negative coupling across five bonds. On the basis of both chemical shifts and coupling constants it was concluded that 1,4-benzoquinones have little aromaticity from the N.M.R. point of view. The halogen atoms in 5,6-dihalogenocyclohex-2-ene-1,4-diones appear to be tram diaxial.

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.

Sigma and Pi Electron Contributions to Long-range Spin–Spin Coupling Constants in the Methyl Derivatives of the Fluoropyridines

1972 ◽  
Vol 50 (14) ◽  
pp. 2344-2350 ◽  
Author(s):  
J. B. Rowbotham ◽  
T. Schaefer
Keyword(s):  
Nitrogen Atom ◽  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
Methyl Group ◽  
Spin Coupling Constants ◽  
Methyl Derivatives ◽  
Spin Spin Coupling ◽  
Derivatives Of

Seven methyl derivatives of the 3- and 4-fluoropyridines are synthesized and their p.m.r. spectra are analyzed. The nuclear spin–spin coupling constants are compared with previous results for the four methyl derivatives of 2-fluoropyridine. A model in which the nitrogen atom polarizes primarily the σ electron system of the ring, leaving the π electron contribution to the coupling mechanism relatively unaffected, qualitatively accounts for the large majority of the coupling constants. For example, the coupling over six bonds between methyl protons and a fluorine nucleus, [Formula: see text] is the same whether the fluorine atom or the methyl group is placed ortho to the nitrogen atom and is little different from its value in p-fluorotoluene. The model is consistent with significant σ electron contributions to long-range couplings over four and five bonds from methyl protons to fluorine nuclei or ring protons. Evidence is adduced for resonance structures in which fluorine conjugates with nitrogen or with ring carbon atoms. An earlier suggestion, that hyperconjugation of the methyl group with nitrogen is necessary to the interpretation of the observed couplings, is dropped. Instead, a substantial polarization of the σ electron core near C-2 and -6 is invoked but apparently does not extend appreciably beyond these atoms in the ring.

scholarly journals Long-range spin–spin coupling in N-methyl 2-carbomethoxy-4,6-dinitroaniline

1970 ◽  
Vol 48 (6) ◽  
pp. 934-941 ◽  
Author(s):  
J. A. McCubbin ◽  
R. Y. Moir ◽  
G. A. Neville
Keyword(s):  
Magnetic Resonance ◽  
Carbonyl Group ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Chemical Shifts ◽  
Relative Magnitude ◽  
Spin Coupling ◽  
Spin Spin Coupling ◽  
Derivatives Of ◽  
Shielding Effects

Long-range coupling [Formula: see text] between the amino proton and the C-5 ring proton of N-methyl 2-carbomethoxy-4,6-dinitroaniline (1) was established unequivocally by comparison of the proton magnetic resonance spectra of the 3-d and 5-d analogs of 1 together with the N-deutero derivatives of the above compounds. Deuterium decoupling experiments indicated that meta-deuterium coupling was of the order of band resolution (< 0.2 Hz). Elucidation of the source of long-range coupling with the amino proton enabled the chemical shifts of the aromatic protons to be assigned. The relative magnitude of these chemical shifts is discussed in terms of the shielding effects operative in the predominant conformer in which the amino hydrogen is intramolecularly hydrogen bonded to the oxygen of the ester carbonyl group.

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.

Electric moments and conformation of substituted fluoroformates in benzene solutions

1968 ◽  
Vol 46 (10) ◽  
pp. 1645-1648 ◽  
Author(s):  
E. Bock ◽  
D. Iwacha ◽  
H. Hutton ◽  
A. Queen
Keyword(s):  
Dipole Moment ◽  
Long Range ◽  
Fluorine Atom ◽  
Dipole Moments ◽  
Experimental Results ◽  
Spin Coupling ◽  
Coupling Mechanism ◽  
Methyl Ethyl ◽  
Hydrocarbon Group ◽  
Spin Spin Coupling

The dipole moments of methyl-, ethyl-, n-propyl-, n-butyl-, n-amyl-, and phenyl-fluoroformate were determined in dilute benzene solutions at 25 °C. The experimental results suggest that the conformation of the fiuoro-esters is similar to the conformation of the chloro-esters and differs from the conformation of the normal esters; viz. the ester hydrocarbon group and the fluorine atom are cis to each other. Results of fluorine and proton n.m.r. measurements on these molecules support the conclusions based on the dipole moment data if a "through-space" coupling mechanism is assumed for the long range spin–spin coupling JH–F1−5.

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