Concerning a relationship between long-range ring proton – methyl proton coupling constants and mobile bond order

1968 ◽  
Vol 46 (4) ◽  
pp. 654-656 ◽  
Author(s):  
D. J. Blears ◽  
S. S. Danyluk ◽  
T. Schaefer
Keyword(s):  
Linear Relationship ◽  
Long Range ◽  
Bond Order ◽  
Coupling Constants ◽  
Methyl Proton ◽  
Methyl Group ◽  
Potential Barriers ◽  
Proton Coupling ◽  
Induced Changes ◽  
Excitation Parameters

Long-range proton – methyl proton coupling constants in propene, mesitylene, 9-methylphenanthrene, and acenaphthene appear to be linearly related to the square of the mobile bond order between the carbon atoms bonded to the methyl group and the proton. However, substituent-induced changes in the charge on and hybridization state of the carbon atoms, in excitation parameters and in potential barriers to rotation of the methyl group, may also affect the coupling. Such changes must be considered in the application of a possible linear relationship.

An Investigation of Substituent Effects on Coupling Constants to Vinyl Protons in Styrene Derivatives

1974 ◽  
Vol 52 (19) ◽  
pp. 3415-3423 ◽  
Author(s):  
William F. Reynolds ◽  
Ian R. Peat ◽  
Gordon K. Hamer
Keyword(s):  
Long Range ◽  
Substituent Effects ◽  
Phenyl Group ◽  
Coupling Constants ◽  
Vinyl Proton ◽  
Model Compounds ◽  
Proton Coupling ◽  
Phenyl Proton ◽  
Styrene Derivatives ◽  
Induced Changes

Experimental long-range phenyl proton–vinyl proton coupling constants in 4-substituted styrenes are substituent independent. This is also predicted by INDO–finite perturbation theory calculations of these coupling constants. Comparison with calculated and experimental long-range coupling constants for 4-substituted benzaldehydes suggests that the previously reported substituent dependence for the latter coupling constants arises from substituent-induced changes in molecular geometry.Geminal vinyl coupling constants in 4-substituted styrenes, α-methylstyrenes, and α-t-butylstyrenes are substituent dependent with substituent effects increasing as phenyl and vinyl groups are twisted out of planarity. These trends are reproduced by INDO–FPT calculations. It is concluded that the substituent effects are primarily transmitted through space.Both experimental and calculated vinyl 13C–1H coupling constants show strong stereospecific substituent effects. From the pattern of results (particularly the greater field dependence for JC(β)H(9) than JC β)H(8)) it is concluded that these coupling constants.also reflect through-space substituent effects. This is supported by calculations on model compounds with no intervening phenyl group.

DOUBLE AND TRIPLE RESONANCE EXPERIMENTS ON 2-BROMO-5-CHLOROTOLUENE: SIGNS OF THE RING AND RING-METHYL PROTON COUPLING CONSTANTS

1966 ◽  
Vol 44 (22) ◽  
pp. 2743-2747 ◽  
Author(s):  
G. Kotowycz ◽  
T. Schaefer
Keyword(s):  
Coupling Constants ◽  
Para Position ◽  
Triple Resonance ◽  
Triple Resonance Experiments ◽  
Methyl Proton ◽  
Methyl Group ◽  
Meta Position ◽  
Proton Coupling ◽  
Polarization Mechanism ◽  
Exchange Polarization

Tickling and decoupling (triple resonance) techniques show that the ortho, meta, and para proton coupling constants have the same sign in 2-bromo-5-chlorotoluene. If the ortho coupling in the ring is positive, then decoupling experiments show that the methyl proton couplings to the ring protons in the ortho and para position to the methyl group are negative, while that to the meta position is positive. These signs are in agreement with the σ–π exchange polarization mechanism.

Relative signs of six proton coupling constants in isopropenylacetylene. The effect of the acetylenic group on the chemical shift of the protons

1967 ◽  
Vol 45 (10) ◽  
pp. 1165-1171 ◽  
Author(s):  
H. M. Hutton ◽  
T. Schaefer
Keyword(s):  
Chemical Shift ◽  
Magnetic Anisotropy ◽  
Long Range ◽  
Triple Bond ◽  
Coupling Constants ◽  
Vector Model ◽  
Methyl Group ◽  
Multiple Resonance ◽  
Proton Coupling ◽  
Acetylenic Group

The relative signs of the six proton coupling constants in isopropenylacetylene have been determined by multiple resonance techniques. The signs of the long-range couplings agree with those predicted by the Dirac vector model. The geminal ethylenic proton coupling is taken as positive. It is concluded that the methyl group does not interact with the triple bond via a hyperconjugative mechanism. The ethylenic protons are less shielded than in propene, whereas the opposite is expected on the basis of the magnetic anisotropy of the triple bond. This apparent anomaly can be rationalized quantitatively with a model given by Castellano and Lorenc and all four shifts relative to propene are predicted satisfactorily.

Assignment of carbon-13 NMR spectra and sign determination of long range carbon-13—proton coupling constants with SPI

1974 ◽  
Vol 6 (8) ◽  
pp. 445-447 ◽  
Author(s):  
A. A. Chalmers ◽  
K. G. R. Pachler ◽  
P. L. Wessels
Keyword(s):  
Long Range ◽  
Nmr Spectra ◽  
Coupling Constants ◽  
Proton Coupling ◽  
Sign Determination

An Investigation of Long-range Proton–Proton Coupling Constants in Phenylacetylene Derivatives

1972 ◽  
Vol 50 (13) ◽  
pp. 2035-2040 ◽  
Author(s):  
C. J. MacDonald ◽  
G. K. Hamer ◽  
I. R. Peat ◽  
W. F. Reynolds
Keyword(s):  
Hyperfine Interaction ◽  
Long Range ◽  
Excellent Agreement ◽  
Quantitative Estimation ◽  
Theoretical Calculations ◽  
Experimental Results ◽  
Coupling Constants ◽  
Proton Proton ◽  
Proton Coupling

Signs and magnitudes of long-range coupling constants in three phenylacetylene derivatives have been determined. Values of the coupling constants are discussed in terms of the McConnell formulation and compared with results of MO–INDO–FPT calculations. Coupling constants are dominated by π contributions. Estimated values of hyperfine interaction constants for acetylene and methylacetylene groups are respectively QCC≡CH = −12 and QCC≡CCH = +12 G. The theoretical calculations are in excellent agreement with experimental results. Both approaches allow quantitative estimation of nine bond couplings in 4-vinylphenylacetylene.

Long range carbon-proton coupling constants in pyridine

1974 ◽  
Vol 6 (3) ◽  
pp. 181-183 ◽  
Author(s):  
Goh Miyajima ◽  
Kensuke Takahashi ◽  
Hiroshi Sugiyama
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Proton Coupling

Structures and conformations of somed-glycero-pent-2-enopyranosyl derivatives and determination of the relative signs of some associated long-range proton coupling constants

Tetrahedron ◽  
1967 ◽  
Vol 23 (5) ◽  
pp. 2395-2412 ◽  
Author(s):  
B. Coxon ◽  
H.J. Jennings ◽  
K.A. McLaughlan
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Proton Coupling
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