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.

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.

P.M.R. spectra of heteroaromatic molecules containing bridgehead nitrogen atoms. II. 5-Methyl-s-triazolo[4,3-a]quinoline and s-Triazolo[4,3-a]quinoline

1976 ◽  
Vol 29 (4) ◽  
pp. 815 ◽  
Author(s):  
ML Heffernan ◽  
GM Irvine
Keyword(s):  
Chemical Shift ◽  
Detailed Analysis ◽  
Long Range ◽  
Coupling Constants ◽  
Order Effects ◽  
Relative Sign ◽  
First Order ◽  
Multiple Resonance ◽  
Bridgehead Nitrogen ◽  
Small Chemical

A detailed analysis of the spectra of 5-methyl-s-triazolo[4,3-a]quinoline and s-triazolo[4,3-a]quinoline in CDCl3 and (CD3)2SO solution was carried out. Measurements were made over a range of temperatures, and multiple-resonance experiments carried out as aids to the confirmation of assignments. The peaks in the spectrum corresponding to H8 were observed to show non-first-order effects, arising from long-range coupling to H4, which were dependent upon the temperature at which the spectrum was obtained. It was found that these effects arose from the variation in the relatively small chemical shift between H6 and H9 and furthermore that the experimental splitting pattern could be used to determine the relative signs of J4,6 and J4,8. Confirmation was obtained that these two coupling constants have the same relative sign.

Signs of long-range amino proton – ring proton coupling constants in N-ethyl-4-chloro-2-nitroaniline

1970 ◽  
Vol 48 (8) ◽  
pp. 1343-1345 ◽  
Author(s):  
T. Schaefer ◽  
R. Wasylishen
Keyword(s):  
Long Range ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Spin Coupling Constant ◽  
Proton Resonance ◽  
Ring Proton ◽  
Multiple Resonance ◽  
Proton Coupling ◽  
Spin Spin Coupling

In N-ethyl-4-chloro-2-nitroaniline there exists a measurable indirect spin–spin coupling constant of ±0.39 ± 0.03 Hz between the methylene protons and ring proton 6. The amino proton is coupled to ring protons 5 and 6 and also to the methylene protons. Consequently, although the amino proton resonance is broad due to incompletely relaxed coupling to 14N, normal multiple resonance experiments show that 5JmH,NH = 0.67 ± 0.03 Hz and 4JoH,NH = −0.35 ± 0.03 Hz.

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

scholarly journals CSSF-CLIP-HSQMBC: measurement of heteronuclear coupling constants in severely crowded spectral regions

RSC Advances ◽  
2019 ◽  
Vol 9 (62) ◽  
pp. 36082-36087 ◽  
Author(s):  
Aitor Moreno ◽  
Kine Østnes Hansen ◽  
Johan Isaksson
Keyword(s):  
Chemical Shift ◽  
Long Range ◽  
Program Development ◽  
Coupling Constants ◽  
Selective Filtration ◽  
User Friendly ◽  
Heteronuclear Coupling

A new pulse program development, a chemical shift selective filtration clean in-phase HSQMBC (CSSF-CLIP-HSQMBC), is presented for the user-friendly measurement of long-range heteronuclear coupling constants in severely crowded spectral regions.

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.

SOLVENT EFFECTS AS AN AID IN THE ANALYSIS OF THE PROTON MAGNETIC RESONANCE SPECTRUM OF VINYL BROMIDE

1960 ◽  
Vol 38 (11) ◽  
pp. 2066-2073 ◽  
Author(s):  
T. Schaefer ◽  
W. G. Schneider
Keyword(s):  
Chemical Shift ◽  
Solvent Effects ◽  
Resonance Spectrum ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Vinyl Bromide ◽  
Proton Coupling ◽  
Geminal Proton ◽  
Geminal Coupling ◽  
Cis And Trans

By making use of specific solvent effects it has been possible to vary the relative chemical shift between the geminal protons of vinyl bromide from about +10 cycles/sec to −4 cycles/sec (at 60 Mc/sec) and to study the resultant changes in the proton resonance spectrum in the limiting region of zero chemical shift. Of particular interest is the growth and displacement of the combination lines, which appear in the resonance signals of the proton bonded to the same carbon atom as the bromine. From the variation of the six possible lines in this region it was confirmed that the cis and trans proton coupling constants must have the same sign. The intensity distribution of the lines in the geminal proton region require the geminal coupling constant to be of opposite sign to the other two.

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