Magnetic Equivalence Research Articles

A Cell-Renormalization Treatment of a Single Polymer Chain

A “cell-scattering transformation” is proposed as a method for a cell-renormalization treatment of a single polymer chain without reference to the magnetic equivalence. In order to demonstrate the basic idea, the one-dimensional random walk problem is treated. Applicability of the method to more practical polymer problems is also discussed.

Magnetic equivalence of the hemes in hemoglobin Zürich.

The magnetic susceptibilities of solutions of deoxyhemoglobin Zürich and deoxyhemoglobin A have been found quite close together, in contrast to previous findings. Therefore, any magnetic inequivalence between alpha- and beta-hemes must be confined to finer details.

Chemical shift equivalence and magnetic equivalence in conformationally mobile molecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChemical shift equivalence and magnetic equivalence in conformationally mobile moleculesRobert M. Silverstein and Robert T. LaLonde Cite this: J. Chem. Educ. 1980, 57, 5, 343Publication Date (Print):May 1, 1980Publication History Received3 August 2009Published online1 May 1980Published inissue 1 May 1980https://doi.org/10.1021/ed057p343RIGHTS & PERMISSIONSArticle Views533Altmetric-Citations5LEARN 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 (2 MB) Get e-Alerts Get e-Alerts

NMR Spectra of the [AX2]2and [A[X]2]2Types: The X Transitions when |JAX| is Large, as in the Case of Tetrafluorodiazadiphosphetidines

AbstractExplicit expressions for X transition frequencies in NMR spectra of [A[X]2]2spin systems are derived for the case where one of the (A. X) coupling constants is much larger in magnitude than any of the other couplings, as is commonly encountered for molecules containing PF2groups. The spectra to be expected are compared with those for the corresponding magnetic equivalence [AX2]2case. Emphasis is placed on the determination of relative signs of coupling constants, and examples of spectra for fluorinated diazadiphosphetidines are discussed.

A proton magnetic resonance study of ligand exchange on pentakis(N,N-dimethylformamide) dioxouranium(VI)ion

Proton magnetic resonance studies show that UO 2(DMF) 2+ 5, pentakis(N,N-dimethylformamide)dioxouranium(VI) ion, is the greatly predominant dioxouranium(VI) species in mixed solutions of DMF and d 2-methylene chloride. The virtual independence of the rate of intermolecular exchange of DMF of free DMF concentration over a 20.3 fold concentration range is interpreted in terms of a dissociative exchange mechanism. A typical set of kinetic data for this process is k ex(220K) = 199 ± 11 s −1, ΔH ♯ = 31.9 ± 0.3 kJ mol −1 and ΔS ♯ = −53.4 ± 1.5 J K −1 mol −1, where the observed exchange rate = 5 k ex[UO 2(DMF) 2+ 5], and the concentrations of UO 2(DMF) 2+ 5, DMF and d 2-methylenechloride are respectively 0.008648, 0.04323 and 15.05 mol dm −3. The observed magnetic equivalence of the methyl groups in bound DMF over the experimental temperature range 170–300 K is shown to arise as a consequence of the cis and trans DMF methyl groups experiencing significantly different magnetic shielding modifications upon coordination to the dioxouranium(VI) ion probably in part as a consequence of the magnetic anisotropy of that ion.

Magnetic equivalence and nonequivalence of methylene groups adjacent to an asymmetric center in a series of .gamma.-phenyl-.gamma.-butyrolactones

Magnetic equivalence and nonequivalence of methylene groups adjacent to an asymmetric center in a series of .gamma.-phenyl-.gamma.-butyrolactones

FT NMR of nonequilibrium states of complex spin systems. II. Weakly coupled systems

Since the Fourier transform NMR spectrum of a nonequilibrium state may be different from the slow-passage spectrum, a theory is developed which describes the phenomenon in any weakly coupled system, including those with magnetic equivalence. Liouville space techniques are used to derive simple expressions for the line intensities as a function of flip angle, in terms of Legendre polynomials. The theory uses F 2 representations directly and is applicable to any weakly coupled system. The results are tabulated for A m X n systems, m, n = 1, 2, 3, and 6. The theory is still applicable when. the weak coupling approximation starts to break down and line intensities are perturbed. It is shown that if the nonequilibrium intensities are corrected by a simple factor, as in the equilibrium case, these systems may be treated as if they were weakly coupled. In practice, the theory may be used to extrapolate to the slow-passage, zero flip angle spectrum. Furthermore, different parts of a degenerate line may be separated by means of the flip angle dependence. As an illustration, a nonequilibrium state was created among the protons in ethyl acetate. The experimental flip angle dependence of its spectra is well represented by the theory.

An unusual magnetic equivalence in the proton magnetic resonance of dialkylbenzamides

An unusual magnetic equivalence in the proton magnetic resonance of dialkylbenzamides

Iterative least-squares nmr lineshape fitting with use of symmetry and magnetic equivalence factorization

A iterative least-squares procedure for the lineshape fitting of high-resolution NMR spectra making use of symmetry and magnetic equivalence factorization is outlined. Parameter refinements of large spin systems are speeded up substantially by the aid of first-order perturbation theory. The program NMRCON handling up to six different chemical shifts is described. Three examples illustrate the application of the program.

Ni(II) Complexes with bis(β-Acylvinyl)amines and (8-Quinolyl-β-acylvinyl)amines

The title complexes have been obtained and shown by elemental analysis, IR and PMR spectra to be octahedral. The trans structure has been assigned to bis(β-acylvinyl)amine complexes based on magnetic equivalence of geminal methyl groups in appropriately substituted representatives of this group of compounds. The (8-quinolyl-β-acylvinyl)-amine complexes may have either trans or s-cis (meso) configuration.

ChemInform Abstract: TETRACYANOETHYLENE COMPLEXES OF NI(0) AND CO(‐1) CONTAINING ISOCYANIDES AND NITROSYL

AbstractDie in kristallinem Zustand beständigen Ni‐ und Co‐Komplexe (I) und (II) werden durch Substitutionsreaktionen entsprechender Tetrakis‐[isocyanid]‐Ni‐ und Nitrosylcarbonyl‐bis‐[isocyanid]‐Co‐Komplexe mit Tetracyanäthylen in Petroläther dargestellt.

Conformation of tetranactin in solution.

AbstractThe conformation of tetranactin, an ionophore, in chloroform was investigated by infrared and Raman spectra and by proton and 13C magnetic resonances. The infrared spectra show that the structure of its K+ complex in the solution is quite similar to that in crystals. The proton spin–spin coupling constants are explained well by assuming that the crystalline structure is retained in solution. The spin–lattice relaxation times of the 13C nuclei of the K+ complex indicate that its framework is rigid. The correlation time of the overall reorientation of the molecule was calculated to be 9 X 10−11 sec. On the other hand, the conformation of the complexed form in chloroform differs from that in crystals. Despite the geometrical nonequivalence of the four subunits in the crystalline state, the nuclear magnetic resonance spectra show their magnetic equivalence in the solution. The proton spin–spin coupling constants have values that are averaged by rapid internal rotation. The spin–lattice relaxation times of the 13C nuclei in its framework are unexplained by the overall reorientation of the molecule, and reveal the existence of internal motion in the framework. The rate of the local motion of the framework is between 102–1010 sec−1. By comparison of the infrared spectra, it can be said that the mean conformation of the fluctuated framework of the uncomplexed tetranactin in the solution is similar to that of nonactin in the crystalline form, which has an S4 symmetry axis through the center of the macrocyclic ring.

Tetracyanoethylene Complexes of Ni(0) and Co(−1) Containing Isocyanides and Nitrosyl

Abstract The magnetic equivalence of the isocyanides in Ni(RNC)3(TCNE) and Co(NO)(RNC)2(TCNE) is more likely to be due to the free rotation of TCNE in solution than to the dissociative exchange of ligands.

Troublesome concepts in NMR spectrometry

Offers definitions, explanations, and suggests references for NMR topics, including spin system, set of nuclei, chemical shift equivalence, magnetic equivalence, and virtual coupling.

Conformations of highly hindered aryl ethers—VIII Interannular HF coupling in diphenyl ethers

AbstractA novel type of interannular coupling (6JH,F = 1.0 to 1.3 Hz) has been observed in some fluorodinitrodiphenyl ethers between the fluorine(s) on one ring ortho to the ether linkage and a proton ortho to it on the other ring. 1H and 19F chemical shift and coupling constant data support the previous conclusion that these ethers preferentially adopt a twist (propeller) conformation. On account of the geometrical disposition of the six bonds between the interacting nuclei and the latter's spatial proximity in this conformation, direct coupling through‐space is indicated. Concerted libration around the ether bonds brings about magnetic equivalence of the o‐fluoro substituents on one ring and causes equal coupling to be observed to the o‐proton on the other ring. The possiblity that the coupling is mediated by an intervening π‐cloud is suggested as an alternate mechanism for indirect coupling. The observed interannular transmission of spin information provides evidence in favor of a recent proposal made concerning the mode of action of the thyroid hormones.

New approach to general theory of electrical machines using magnetic equivalent circuits

First, the nature of equivalent circuits and the alternative electric or magnetic equivalents for any electromagnetic system are examined. In the remaining Sections, steady-state and symmetrical sudden short-circuit conditons are analysed for the3-phase synchronous, the 3-phase induction and the compounded d.c. machine, using the magnetic-equivalent representation. Results are obtained more easily than by the conventional procedure. Also, since the method of analysis is the same for each of the cases considered, results obtained for one type of machine can often be applied to another and the approach is truly general.

Untersuchungen der Symmetrieverhältnisse in äquatorial koordinierten 2:1‐Arylazo‐CoIII‐Komplexen mit Hilfe der Protonenresonanz

AbstractThe magnetic equivalence of ligand protons was examined with aid of NMR. spectroscopy for a large number of 1:2 CoIII‐complexes of tridentated azo dyestuffs forming a representative cross section of the whole class of substances. It was established by this investigation that ligands with a moderately polarised azo group have a particular inclination to form asymmetrical complexes in which the protons of the two ligands are not magnetically equivalent. On the other hand, ligands having a non‐polarised or a strongly polarised azo group tend to form symmetrical complexes. In three cases both symmetrical and asymmetrical complexes were isolated. As in previous investigations [1], up to a total of 5 complexes were again observed, which indicates at least two causes governing the symmetry conditions. The phenomena described here could be explained with an alternative coordination of the two azo nitrogen atoms. On the basis of the NMR. results, however, preference is given to an exchange of the azo with the hydrazone form.

NMR spectra of symmetric molecules. I. The spin Hamiltonian for twofold symmetry

Symmetrized spin operators and an appropriate symmetrized basis greatly simplify the calculation of the NMR spectra of molecules with twofold symmetry. The Hamiltonian is factored to the full extent permitted by the twofold symmetry and any magnetic equivalence that is present. Equations are given to permit the calculation of all necessary matrix elements directly from the spin quantum numbers. Even for molecules with symmetrically equivalent pairs of magnetically equivalent groups, the usual laborious expansion of the symmetrized basis in terms of the original unsymmetrized basis is eliminated.

Exchange Averaging of Methylol Groups Attached to Phosphorus

Variable temperature 1H n.m.r. spectra of pyridine solutions of tetrakis(hydroxymethyl)phosphonium chloride indicate that chemical exchange of methylol groups of the salt with those of the small amount of tris(hydroxymethyl)phosphine formed is the cause of their magnetic equivalence at elevated temperatures. Triethylamine transforms the salt into the phosphine and at least two other phosphorus species which may result from reaction of formaldehyde at oxygen of the phosphine.

Fluorine-19 nuclear magnetic resonance studies of methyl-substituted piperidylfluorophosphoranes

19 F n.m.r. data are presented for 2-methyl-,3-methyl-, and 4-methyl-piperidylfluorophosphoranes in which the magnetic equivalence or non-equivalence of the axial or equatorial fluorine atoms is dependent on the position of the methyl group on the piperidyl ring and position of the ring with reference to the trigonal bipyramidal structure.