Spin Decoupling Research Articles

Studies on the constituents of Chondria armata. 8. On the structure of domoic acid. (1)

The NMR spectrum of domoic acid (in CF3COOH) indicates signals for a methyl at 1.43 p.p.m. (d;J=6.6 c.p.s.) and at 1.94 p.p.m. (a broad singlet), and no signal for an ethyl group. The methyl signal at 1.94 p.p.m. shows a long-range I-I coupling due to spin decoupling. The NMR spectrum of trimethyl domoate (in CDCl3) shows a doublet methyl (J=7.0 c.p.s.) at 1.29 p.p.m., a methyl signal which indicates an allylic coupling at 1.79 p.p.m., and an olefinic proton signal corresponding to 3H at 5.5∼6.6 p.p.m. From its first-order analysis, the configuration of the 1, 3-hexadienyl side chain was determined as trans : trans : S-trans. The infrared spectra of both domoic acid and trimethyl domoate show absorption due to the trans-double bond. The NMR spectrum of tetrahydrodomoic acid (in CF3COOH) shows signals for a methyl bonded to a secondary carbon at 1.12 p.p.m. (d;J=6.0 c.p.s.) and at 1.22 p.p.m. (d;J=6.6 c.p.s.). It was concluded from these observations that the structure of domoic acid would be more appropriately represented as Ls-arabo-2-carboxy-4-(1-methyl-5-carboxy-trans : trans : S-trans-1, 3-hexadienyl)-3-pyrrolidineacetic acid (VIII) rather than the previously proposed Ls-arabo-2-carboxy-4-(1-methyl-2-carboxy-1, 3-hexadieny1)-3-pyrrolidineacetic acid (I).

Conformational Studies in the 2-Azabicyclo [3.2.2] nonene Series by Spin Decoupling. Structure of the N-Carbethoxyazepine-Tetracyanoethylene Adduct

Conformational Studies in the 2-Azabicyclo [3.2.2] nonene Series by Spin Decoupling. Structure of the N-Carbethoxyazepine-Tetracyanoethylene Adduct

SUBSTITUTIONAL AND CONFIGURATIONAL EFFECTS ON CHEMICAL SHIFT IN PYRANOID CARBOHYDRATE DERIVATIVES

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.

Investigation of polyacetaldehyde structure by high resolution nuclear magnetic resonance

AbstractWe examined the configurations of cationically produced amorphous polyacetaldehyde by high resolution NMR spectroscopy at high temperature in such solvents as dimethylformamide and aniline. Our results show that the polymer backbone is composed of heterotactic and isotactic triad sequences, the former predominating over the latter. Using a 60 Mcycle instrument with or without spin decoupling, we were unable to detect any syndiotactic triad sequences. In addition, the 60 Mcycle NMR spectrum of poly‐α‐deuteroacetaldehyde shows the presence of only the same two stereochemical triads as above. However, examination of polyacetaldehyde with a 100‐Mcycle instrument indicated that a small shoulder exists on the low field side of the heterotactic peak which is probably caused by a small syndiotactic triad content. We used these findings to propose a mechanism for the cationic polymerization of acetaldehyde. We suggest that acetaldehyde may exist in a dimeric form under polymerization conditions leading to a preferred incorporation of mesodimeric units into the propagating chain. Model compound studies involving α,α′‐dimethoxyethyl ether are consistent with this postulate.

Undecoupled and decoupled high resolution nuclear magnetic resonance study of poly(vinyl chloride)

AbstractHigh resolution nuclear magnetic resonance spectra of two kinds of poly(vinyl chloride) and the model compounds, meso and racemic 2,4‐dichloropentane were studied by normal and spin decoupling technique to elucidate the polymer structure. Unlike the methylene resonance of meso 2,4‐dichloropentane which has been observed as an AB type quartet, only a singlet has been observed as the methylene resonance in isotactic sequences of poly(vinyl chloride) in spin‐decoupled spectra. Two peaks of decoupled spectra of the polymer at 7.76 and 7.96 τ are due to methylene protons in isotactic and syndiotactic sequences in the diad, respectively, and the other three peaks at 5.43, 5.53, and 5.69τ correspond, respectively, to syndiotactic, heterotactic, and isotactic units in the triad. By analyzing decoupled spectra of the two kinds of polymer, parameters of local regularity have been determined. A theoretical treatment for the spectrum for four nuclei ABX2 has been applied to analysis of the methylene resonance of meso 2,4‐dichloropentane.

Application of Spin Decoupling and 100-Megacycle Spectra to Characterization of Carbohydrates. Novel Synthesis of a Cyclohexanetetrol1,2

Application of Spin Decoupling and 100-Megacycle Spectra to Characterization of Carbohydrates. Novel Synthesis of a Cyclohexanetetrol^1,2

The structure of cis, cis, cis-1,4,7-cyclononatriene determined by proton-proton spin decoupling

The structure and conformation of cis, cis, cis-1,4,7-cyclononatriene has been proved by proton-proton spin decoupling experiments carried out with both the “frozen” and rapidly inverting hydrocarbon.

TAUTOMERISM AND SITE OF PROTONATION OF 1-METHYLCYTOSINE: PROOF BY NUCLEAR MAGNETIC RESONANCE SPIN-SPIN COUPLING.

New nuclear magnetic resonance data lead to a completely unambiguous proof that the predominant tautomeric form of 1-methylcytosine is the amino form and that in acid solution the molecule protonates at 3-N. The close similarity of the nuclear magnetic resonance spectra of this compound to the spectra of the cytosine nucleosides indicates that these structures also exist in the nucleosides. These conclusions are reached on the basis of the spectra of analogs labeled with N15 and of the proton spin decoupling measurements made at low temperature.

Fluorine—Fluorine Nuclear Spin—Spin Decoupling

Fluorine—Fluorine Nuclear Spin—Spin Decoupling

159. Proton–proton spin decoupling by single sideband modulation

159. Proton–proton spin decoupling by single sideband modulation

THE USE OF A PROTON-PROTON SPIN DECOUPLING METHOD FOR THE DETERMINATION OF NUCLEAR MAGNETIC RESONANCE CHEMICAL SHIFTS

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTHE USE OF A PROTON-PROTON SPIN DECOUPLING METHOD FOR THE DETERMINATION OF NUCLEAR MAGNETIC RESONANCE CHEMICAL SHIFTSStanley L. Manatt and Daniel D. EllemanCite this: J. Am. Chem. Soc. 1961, 83, 19, 4095–4096Publication Date (Print):October 1, 1961Publication History Published online1 May 2002Published inissue 1 October 1961https://doi.org/10.1021/ja01480a035RIGHTS & PERMISSIONSArticle Views32Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (270 KB) Get e-Alerts Get e-Alerts

Spin decoupling in high resolution proton magnetic resonance

A simple unit is described which can be incorporated in a high resolution nuclear magnetic resonance spectrometer to remove the spin coupling between two groups of hydrogen nuclei in the same molecule. Applied to the molecule of propionaldehyde, the method considerably simplifies the analysis of the high resolution spectrum measured at 60 Mc/s.

Concluding remarks

I shall not attempt to make a lengthy critical assessment of all that we have heard today. We have been given a wealth of new experimental results, and have been shown some stimulating approaches on the theoretical side. Yet it might be difficult to draw any clear conclusion other than that there is a need for much more experimental work if we are to disentangle the complex of intermolecular interactions of the different kinds. Among these interactions we have discussed dipole-dipole, London dispersion (induced dipole), and quadrupole effects, spin decoupling and repulsion overlap, ‘field’ effects and ion-pair perturbations. They are manifest in the changes produced in the electronic, vibrational, rotational or nuclear spin energy levels. A solvent perturber can cause blue or red shifts of the electronic spectra by displacement of either the lower or upper electronic level concerned in the transitions. Some progress has been made in the interpretation of such shifts. We have been told about the astonishing effects of perturbing molecules upon the intensities of certain electronic absorption bands, such as the influence of minute amounts of dissolved oxygen on the absorption of benzene, where the paramagnetic disturber appears to affect the singlet-triplet transition through spin-orbital decoupling