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.

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.

P.M.R. spectra of heteroaromatic molecules containing bridgehead nitrogen atoms. III. Pyrrolo[2,1-c][1,2,4]benzotriazine

1976 ◽  
Vol 29 (4) ◽  
pp. 827 ◽  
Author(s):  
ML Heffernan ◽  
GM Irvine
Keyword(s):  
Acetic Acid ◽  
Acid Solution ◽  
Long Range ◽  
Acetic Acid Solution ◽  
Dimethyl Sulphoxide ◽  
Coupling Constants ◽  
Relative Sign ◽  
Favourable Case ◽  
Bridgehead Nitrogen

The detailed assignment and analysis of the p.m.r. spectra of solutions of pyrrolo[2,1-c][1,2,4]benzotriazine in dimethyl sulphoxide at 80� and 100�, and in acetic acid at 60�, was carried out. The presence and approximate magnitudes of several inter-ring long-range coupling constants were deduced by comparison of the experimental and theoretically calculated spectra. Spin-tickling experiments were used to determine the relative sign combinations of the intra-ring coupling constants of the protons 1-3 and 6-9 in the particularly favourable case of the acetic acid solution of pyrrolo[2,1-c][1,2,4]benzotriazine. All coupling constants were found to have the same sign, presumably positive.

P.M.R. spectra of heteroaromatic molecules containing bridgehead nitrogen atoms. I. Tetrazolo[1,5-a]quinoline and 5-Methyltetrazolo[1,5-a]quinoline

1976 ◽  
Vol 29 (4) ◽  
pp. 799 ◽  
Author(s):  
ML Heffernan ◽  
GM Irvine
Keyword(s):  
Nitrogen Atom ◽  
Long Range ◽  
Coupling Constants ◽  
Triple Resonance ◽  
Relative Sign ◽  
Coupling Constant ◽  
Triple Resonance Experiments ◽  
Aromatic Molecules ◽  
Bridgehead Nitrogen

This paper is the first of a series dealing with the analysis of the 100-MHz p.m.r, spectra of hetero-aromatic molecules containing a bridgehead nitrogen atom as part of the conjugated system, e.g. pyrrolo[l,2-a]quinoline. The spectra of the aza-substituted derivatives tetrazolo[l,5-a]quinoline and 5-methyltetrazolo[l,5-a]quinoline in Me2SO and CDCl3 solutions are analysed in detail. Special attention was directed to the determination of the long-range inter-ring coupling constants and their relative signs by multiple-resonance techniques. The analysis of the spectrum of the 5-methyl compound was considerably simplified by decoupling of the methyl protons from the remainder. Evidence was found for a five-bond long-range coupling constant, J4,6, and a seven-bond coupling constant, J4,8 both having a magnitude around 0.3 Hz. Selective double and triple resonance experiments indicated that the relative sign of both of these long-range coupling constants was positive.

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.

SUBSTITUTIONAL AND CONFIGURATIONAL EFFECTS ON CHEMICAL SHIFT IN PYRANOID CARBOHYDRATE DERIVATIVES

1965 ◽  
Vol 43 (7) ◽  
pp. 2059-2070 ◽  
Author(s):  
R. U. Lemieux ◽  
J. D. Stevens
Keyword(s):  
Chemical Shift ◽  
Long Range ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Equatorial Orientation ◽  
Free Energies ◽  
Bonding Interaction ◽  
Conformational Properties ◽  
Good Agreement ◽  
Shielding Effects

The effects of long-range and virtual long-range coupling on the observed spectra of acetylated hexopyranoses and pentopyranoses are examined. Use is made of both spin decoupling and specific deuteration for the assignment of signals. It is seen that specific solvent effects on chemical shift can be superior to increasing the applied magnetic field for the resolution of the signals of closely related protons. The alteration of virtual long-range coupling effects in these ways can be useful in the diagnosis of spectra. Empirical rules are derived for estimating the long-range shielding effects which occur on changing configurations. It is seen that the inversion of a center can lead to deshielding of axial protons and to shielding of equatorial protons at other centers relative to the chemical shifts observed in reference compounds wherein all the acetoxy groups are in equatorial orientation. The effects in several cases result in equatorial protons giving their signal to higher field than chemically similar but axial protons. The conformational properties of pentopyranose tetraacetates as estimated from chemical shifts and coupling constants are seen to be in good agreement with expectations based on non-bonding interaction free energies. As expected, 2-deoxy-β-D-ribopyranose triacetate has the 1C-conformation when dissolved in chloroform.

13C and some 15N N.M.R. spectra of heteroaromatic molecules containing bridgehead nitrogen atoms

1980 ◽  
Vol 33 (3) ◽  
pp. 499 ◽  
Author(s):  
AJ Jones ◽  
P Hanisch ◽  
ML Heffernan ◽  
GM Irvine
Keyword(s):  
Electronic Structures ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Methyl Substitution ◽  
First Order ◽  
Degree Of Aromaticity ◽  
Bridgehead Nitrogen ◽  
High Degree ◽  
Free Pair

The carbon-13 and (in part) nitrogen-15 chemical shifts of 1,2,3- triazaindolizine and seven three ringed analogues of indolizine have been analysed and enable deductions to be made concerning the extent that the free pair of electrons on the bridgehead nitrogen atom contributes to the delocalized electronic structures. Analogies between these molecules and indolizine are noted in that all the systems possess a high degree of aromaticity. Additivity relationships for nitrogen and methyl substitution are compared with those previously reported for other heteroaromatic molecules. Comparison of previously published 100-MHz and the present-work 270-MHz proton n.m.r. results enabled 13C spectral assignments to be confirmed by selective 1H irradiation experiments, since coupling constant analyses did not provide unambiguous assignments in all cases. One-, two-, three- and four-bond 13C-1H coupling constants are reported for most carbon atoms where first-order spectral analysis was possible. Several examples of non-first-order behaviour are presented and attempts to reconcile the occurrence of this behaviour are outlined.

scholarly journals Application of multiplet structure deconvolution to extract scalar coupling constants from 1D NMR spectra

2021 ◽  
Author(s):  
Damien Jeannerat ◽  
Carlos Cobas
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Second Order ◽  
Coupling Constants ◽  
Scalar Coupling ◽  
Order Effects ◽  
Robust Method ◽  
Multiplet Structure ◽  
First Order ◽  
Coupling Structure

Abstract. Multiplet structure deconvolution provides a robust method to determine the values of the coupling constants in first-order 1D NMR spectra. Functions simplifying the coupling structure for any spins and for doublet with unequal amplitudes were introduced. The chemical shifts of the coupling partners causing mild second-order effects can, in favourable cases, be calculated from the slopes measured in doublet structures. Illustrations demonstrate that deconvolution can straightforwardly analyse multiplet posing difficulties to humans and, in some cases, extract coupling constants from unresolved multiplets.

NMR Spectroscopic Studies of Thialene (Cyclopenta[b]thiapyran) and Isothialene (Cyclopenta[c]thiapyran)

1993 ◽  
Vol 58 (1) ◽  
pp. 113-120 ◽  
Author(s):  
Robert F. X. Klein ◽  
Václav Horák ◽  
Arthur G. Anderson
Keyword(s):  
Chemical Shift ◽  
Bond Order ◽  
Spectroscopic Studies ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Vicinal Coupling Constant ◽  
Spectral Parameters ◽  
First Order ◽  
Nmr Techniques ◽  
C Nmr

1H and 13C NMR spectral parameters are reported for the S-pseudoazulenes thialene (cyclopenta[b]thiapyran) (I) and isothialene (cyclopenta[c]thiapyran) (II). Both compounds display complex first order spectra, with thialene having 10 and isothialene 14 of 15 possible coupling constants. Complete unambiguous assignments of all protons and non-quaternary carbons were made via 2-dimensional NMR techniques and PPP-SCF π-electron density/chemical shift and π-bond order/vicinal coupling constant correlations.

C13 SPLITTINGS IN SOME SUBSTITUTED BENZENES

1962 ◽  
Vol 40 (9) ◽  
pp. 1758-1762 ◽  
Author(s):  
H. M. Hutton ◽  
W. F. Reynolds ◽  
T. Schaefer
Keyword(s):  
Long Range ◽  
Electron Acceptors ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Substituted Benzenes ◽  
First Order ◽  
Proton Coupling

C13 sidebands in the proton spectra of some symmetrically substituted benzenes have been used to obtain carbon–hydrogen coupling constants as well as proton coupling constants.A long-range carbon–hydrogen coupling constant has also been found. Substituents which act as electron acceptors in an inductive manner are found to increase the C13H coupling constants by as much as 20 c.p.s. The patterns of the sidebands are discussed and possible errors in first-order analyses are indicated.

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