Proton Resonance Spectra Research Articles

Proton resonance spectra of some unsaturated carboxylic acids

The proton resonance spectra of some α-β unsaturated carboxylic acids in aqueous solutions in the pH range 0–9 have been measured and are discussed with reference to the ionization sequences. The shifts produced by adding Co2+ ions are interpreted in terms of complex formation.

Proton resonance spectra of N,N-dimethylaniline and deuterated derivatives

Proton resonance spectra of N,N-dimethylaniline and deuterated derivatives

Cyclopentadienides of ytterbium (III) and ytterbium (II)

The reaction of anhydrous ytterbium (III) chloride with sodium cyclopentadienide followed by crystallization from tetrahydrofuran (THF) gives the tetrahydrofuranate Yb(C 5H 5) 3 · C 4H 8O (I), which can easily be converted into the ammoniate Yb(C 5H 5) 3 · NH 3 (II) by treatment with the stoichiometric amount of ammonia. Ytterbium tricyclopentadienide free from any additional Lewis base can only be obtained by using Fischer's method consisting of reacting YbCl 3 with KC 5H 5 in toluene. The emerald-green diamagnetic Yb(C 5H 5) 2 (IV) was prepared by reducing Yb(C 5H 5) 2Cl with finely dispersed sodium metal. Infra-red, visible and ultra-violet absorption spectra and proton resonance spectra confirm the proposed formulations. All the available data strongly suggest the view that the bonding between the ytterbium and the C 5H 5 − rings is essentially ionic in character in all the compounds described in this paper.

Optically active co-ordination compounds. Part VII. Tris-complexes of (+)-hydroxymethylenecamphor

The tris-complexes of (+)-hydroxymethylenecamphorate with chromium(III), cobalt(III), and rhodium(III) have been investigated in detail. The geometrical-optical isomers obtained pure are characterised by studies of electronic, and proton resonance spectra, and Cotton effect. The isomers obtained from cobalt(III) are D-1,2,3-(–)[Co(+hmc)3] and D-1,2,6-(–)-[Co(+hmc)3], while the sole isolable product containing chromium(III) is D-1,2,6-(+)-[Cr(+hmc)3], though an unstable L-isomer may also exist. However, with rhodium(III), the isomers D-1,2,6-(–)-[Hh(+hmc)3] and an L-isomer, probably L-1,2,6(+)-[Rh(+hmc)3] were isolated. A distinction is made between kinetic and thermodynamic control of stereoselectivity in complexes. The absolute configurations of all the isolated isomers of [M(+hmc)3] are given. The variation of optical rotatory power of (–)-[Co(+hmc)3] as a function of solvent is presented, and correlated with properties of the solvent and of the complex, in particular its absorption spectrum.

Proton resonance spectra and tacticity of poly-2-vinylpyridine

Proton resonance spectra and tacticity of poly-2-vinylpyridine

Proton and fluorine N.M.R. spectra of fluorobenzene

Proton and fluorine resonance spectra of fluorobenzene have been obtained under high resolution using a Varian spectrometer operating at 100 Mc/s and 94·1 Mc/s respectively. These have been analysed by treating the molecule as a six-spin system off the type AB 2 C 2 X with C 2v symmetry. The best parameters available were used to solve the secular equation using an IBM 1620 computer. Carbontetrachloride, chlorform, dioxan and benzene were used as solvents and spectra were obtained at different concentrations. Both 1H and 19F spectra show concentration dependence. Splittings of the spectra due to the natural abundance of 13C were observed. The coupling constants J 13C-H and J 13C-F have the values 160·0±2·0 c/s and 265·5±2·0 c/s respectively.

Nuclear magnetic resonance spectra of protons and structure of azines and phenylhydrazones

1. The high-resolution PMR spectra of azines, phenyl- and methylphenyl-hydrazones of aliphatic ketones and aldehydes were obtained and deciphered. 2. On the basis of an analysis of the data obtained, conclusions were drawn on the hydrazone structure of the compounds studied in the free state. 3. Using the data obtained and the theory of the magnetic anisotropy of aromatic rings, calculations were made of the probable configuration of the acetaldazine, dimethylketazine, acetone phenyl- and methylphenyl-hydrazones, and acetaldehyde methylphenylhydrazone molecules. 4. A study of the influence of temperature on the PMR spectrum of acetone methylphenylhydrazone within the interval from −14 to +80° indicated the absence of free rotation of the phenyl radical around the C-N bond.

Rotational isomerism

A calculation of the energies of the dipolar and quadrupolar electric fields of a 1,2-disubstituted ethane and their dependence on the dielectric constant of the medium gave results in good agreement with experiment for the energy differences between the rotational isomers in the gas and liquid phases. The theory is used to derive the proton-proton and proton-fluorine coupling constants of the rotational isomers of 1-chloro-2-bromo, 1-chloro-2-fluoro and 1-bromo-2-fluoro ethane from the solvent dependence of the proton resonance spectra. Notable deviations from this classical theory are found with aromatic solvents and are due to specific interactions of the solvents with the more polar rotational isomer. The theory also shows that the energy difference between the rotational isomers in the liquid phase is not constant but a function of temperature, and the determination of the coupling constants of the individual isomers from the temperature dependence of the spectrum is shown to be critically dependent on the assumptions made concerning this energy difference. The coupling constants obtained show the effects of the orientation of the substituents in that J g HH in the trans isomer (5·1–5·5 c.p.s.) is almost twice that in the gauche isomer (2·7–2·2 c.p.s.). J t HF equals 53 c.p.s., a much larger value than has hitherto been reported. Consideration of these and other couplings in similar ethane-like fragments leads to the conclusions that J t is much more dependent on the substituents on the carbon atoms than J g. The latter is only dependent on the nature of the substituents which are in a trans orientation to the coupling nuclei.

Nuclear magnetic resonance spectra of some inorganic ring systems. Part 1.—Proton resonance spectra of 1,3-diaza-2-thiacyclopentanes

The proton magnetic resonance spectra of the ring systems (I) and (II) below show that there is a non-equivalence of the protons in both the ring-methylene and ethyl-methylene groups for all compounds, with the exception of the ring-methylene protons in (II). The non-equivalence in each case is attributed to the presence of the sulphoxide or sulphone group. The asymmetry at the sulphur atom, causing the absence of a plane of symmetry in the five-membered ring, is the primary cause of ring-methylene non-equivalence. The absence of a plane of symmetry containing the N—R bond makes the side-chain methylene protons non-equivalent, but an additional factor may be the restricted rotation about the C—N bond. The spectra are analyzed to evaluate chemical shifts and coupling constants, and a theoretical spectrum is computed for the methylene signals of (I)(R = Et).

Proton resonance spectra and stereochemical configuration of poly(vinyl acetate) and its model compounds

Proton resonance spectra and stereochemical configuration of poly(vinyl acetate) and its model compounds

Nuclear Spin Relaxation and Double Resonance in HD Gas

Nuclear magnetic double-resonance experiments were performed on a gaseous sample containing a mixture of HD and C${\mathrm{O}}_{2}$ at high pressure by observing the spin-spin multiplet in the proton-resonance spectrum and irradiating either the deuteron transitions or some of the proton transitions. The spectra show features arising from spin relaxation in HD. These features are analyzed by using the density-matrix theory of double resonance, assuming "strong"- and "weak"-collision models for the system. The equation of motion of the spin density matrix is exactly of the same form for both collision models, the only distinction coming from the dependence of the correlation times on the transformation properties of the lattice operators and on the quantum numbers characterizing the lattice states. The results of the analysis of HD double-resonance spectra indicate that the collisions in this case are "strong." The cross products between lattice terms which transform identically but belong to two different relaxation mechanisms make significant contributions to some of the correlation functions involved and thereby affect the final results.

Spektroskopische untersuchungen an organometallischen verbindungen : XXXIII. 1H-NMR-spektren von σ-cyclopentadienylen von metallen der IV. Gruppe

The proton resonance spectra of metal σ-cyclopentadienyls of Group IV at various temperatures are reported and discussed in terms of a valency tautomerism.

REACTIONS OF AMIDES AND RELATED COMPOUNDS: I. N.M.R. (PROTON) INVESTIGATION OF N,N-DIMETHYLFORMAMIDE – LEWIS ACID ADDUCTS AND REMARKS ON THE RELATIVE STRENGTH OF LEWIS ACIDS

The proton resonance spectra of a number of Lewis acid – N,N-dimethylformamide adducts in 2-nitropropane and methylene chloride solutions have been investigated and an attempt has been made to correlate the relative strength of Lewis acids with the chemical shift of the methyl protons. The order obtained for the relative strength of Lewis acids shows good agreement with the results obtained by other methods. The complex formation has taken place on the carbonyl oxygen of the N,N-dimethylformamide in all cases. The DMF – Lewis acid mole ratios were 1:1 in ZnCl2, AlCl3, PF5, BiCl3, InCl3, AsF5, SbCl5, SbF5, BF3, BCl3, BBr3. The 2:1 DMF – Lewis acid complexes of ZnCl2, SnCl4, SnBr4, Snl4, TiCl4, ZrBr4 have also been investigated.

Assignment of the proton magnetic resonance spectra of some tris-(diethylphenylphosphine) complexes of Re(III), Re(IV), Ir(III) and Rh(III)

Proton resonance spectra are reported for ReCl3(PMe2Ph)3, ReCl3(PEt2Ph)3, ReCl4(PEt2Ph)2, IrCl3(PEt2Ph)3, RhCl3(PEt2Ph)3 and for the free phosphine ligand. The spectra are assigned on the basis of diamagnetic behaviour for Ir(III) and Rh(III), paramagnetic behaviour for Re(III) and Re(IV), and meridial octahedral structures (C 2v symmetry) for the M(III) complexes. Spectral peculiarities are: (i) ‘virtual coupling’ of protons in alkyl groups to the two mutually trans phosphorus atoms in the diamagnetic complexes; (ii) large shifts arising from contact or pseudo contact mechanism in the paramagnetics; (iii) lack of phosphorus-hydrogen and small (<7 c/s) hydrogen-hydrogen couplings in the paramagnetics, and (iv) inequivalent methylene protons in the ethylphosphine complexes.

49. Conformational studies of six-membered heterocyclic compounds. Part I. The proton resonance spectra of some substituted 1,3-dithians

49. Conformational studies of six-membered heterocyclic compounds. Part I. The proton resonance spectra of some substituted 1,3-dithians

39. The A2B2 proton resonance spectrum of 2-methyl-1,3-dioxolan

The first page of this article is displayed as the abstract.

Computer Analysis of NMR Spectra: Magnetic Equivalence Factoring

An extension of the NMR analysis method of Swalen and Reilly is described. The Hamiltonian matrix is factored to reduce it to minimal dimension by taking advantage of magnetic equivalence. Significant improvements are obtained in computation speed, computer program capacity, and convenience of use. Other extensions of the method provide a thorough statistical assessment of the resulting parameter estimates, and permit a solution even when some of the energy levels do not participate in any of the assigned transitions. The method has been tested by analyzing the 60-Mc/sec proton resonance spectra of propane (A6B2) and isobutane (A9B). The chemical shifts, downfield from internal tetramethylsilane, and the coupling constants are: CH3CH2CH3; δ(CH3) = 0.912±0.005 ppm, δ(CH2) = 1.350±0.005 ppm, J = 7.35±0.02 cps: (CH3)3CH; δ(CH3) = 0.900±0.005 ppm, δ(CH) = 1.738±0.005 ppm, J = 6.73±0.05 cps.

Proton resonance study of antiferromagnetic FeCl 2.4H 2O

The proton resonance spectrum of FeCl 2.4H 2O has been examined in the temperature range 4.2°K to 0.35°K. We find: 4.2—1.1°K-lines characteristic of the paramagnetic state; 1.1—0.7°K — no lines; 0.7—0.35°K — lines characteristic of the antiferromagnetic state. Using the observed local fields and symmetry arguments a structure for the antiferromagnetic spin arrangement is proposed.

Studies on Nickel(II) Complexes. VI. The Conformational Equilibria of Bis(o-hydroxynaphthaldimine) Complexes

The existence of a planar ⥨ tetrahedral structural equilibrium in solutions of three isomeric groups of bis(o-hydroxynaph-thaldiminej—Ni(II) complexes has been established from studies of magnetic susceptibilities, ligand field spectra, and proton magnetic resonance spectra. Like the related salicylaldimine complexes, 1 these naphthaldimine complexes manifest isotropic hyperfine contact shifts in their proton resonance spectra. The assignment of these spectra is discussed. The sign of the contact shifts and spin densities are shown to be in agreement with a qualitative valence bond model of spin delocalization. The use of the contact shift effect in obtaining cis spin-spin coupling constants is illustrated for one o-hydroxynaph-thaldimine system.

Proton resonance spectra and tacticities of some poly(methyl vinyl ethers)

AbstractMethyl vinyl ether has been polymerized by BF3 etherate catalyst under a variety of conditions to obtain polymers of different molecular weights and tacticities. Some properties of these polymers have been compared with those of a sample prepared with a special stereoregulating catalyst at the Hercules Powder Company. The proton magnetic resonance spectra of poly(methyl vinyl ether) in several solvents have been investigated and it has been possible to assign the absorptions by the methoxyl protons to particular steric configurations of the polymer chain. These data have been used to compare the tacticities of the different polymer samples and to establish that good steric control in the propagation reaction is possible with a soluble BF3 etherate catalyst.