Search results for "NMR spectra"

Defect reactions of implanted Li in ZnSe observed by β-NMR

2001

Abstract Using β-radiation detected nuclear magnetic resonance (β-NMR), we investigated the microscopic behavior of implanted 8 Li in nominally undoped ZnSe crystals. From the temperature-dependent amplitudes of high-resolution NMR spectra we conclude a gradual interstitial-to-substitutional site change between 200 and 350 K . This is in accordance with earlier emission channeling results. We argue that this conversion proceeds via Lii++VZn2−→LiZn− and involves implantation related Zn vacancies.

Influence of data treatment on the shape of 2H NMR T1 curves

1993

A new interpretation of 2H T1 data of glass-forming systems in the range of the range of the caloric glass transition temperature has been proposed. It is shown that with the traditional treatment of the data the timescale of structural relaxation has an influence on the observed spin-lattice relaxation times. Avoiding this problem with a different treatment of the experimental data, it is possible to compare the 2H T1 data directly with corresponding 1H data.

Aluminum-27 double-rotation NMR investigations of SAPO-5 with variable silicon content

1995

Summary Double-rotation NMR (DOR) studies of 27 Al species in SAPO-5, a silicon aluminophosphate molecular sieve with a one dimensional channel system, have revealed a minimum of three aluminum sites resulting from the synthesis. The DOR technique was used specifically to increase the spectral resolution by removing the broadening influences from second-order quadrupolar interactions associated with the spin 5/2 27 Al nuclei. The DOR investigations of SAPO-5 crystals with variable Si/Al ratios resulted in the identification of three aluminum species, two consistent with the reported isotropic shift values for AlPO 4 -5; however, these two resonances are only observable when small quantities…

One Dimensional and Two Dimensional NMR Spectra by Modern Pulse Techniques. Herausgegeben von K. Nakanishi. University Science Books, Mill Valley (US…

1992

87RbNMR spectra of hydrogen-bondedRb3D(SO4)2andRb3H(SO4)2crystals

1999

The paraelectric and antiferroelectric phases of ${\mathrm{Rb}}_{3}{\mathrm{D}(\mathrm{S}\mathrm{O}}_{4}{)}_{2}$ and ${\mathrm{Rb}}_{3}{\mathrm{H}(\mathrm{S}\mathrm{O}}_{4}{)}_{2}$ were investigated using rubidium NMR. The angle dependence of the second order quadrupole shifted central ${}^{87}\mathrm{Rb}$ transitions was recorded at 300 K. It was found to be in full agreement with the symmetry elements of a monoclinic $A2/a$ structure. The temperature dependence of the magnitude and asymmetry of the electrical field gradient (EFG) tensors at the Rb sites was determined using powder samples and revealed no differences between protonated and deuterated specimens. The antiferroelectric transi…

Symmetry: Friend or foe?

1999

While symmetry in molecules or supramolecular complexes is desirable from the design point of view and affords simpler NMR spectra, the study of symmetrical species by NMR is often subject to ambiguities resulting from signal degeneracy. In this paper we shall discuss different ways of breaking symmetry in order to obtain additional structural information by NMR.

The combined effects of two chlorine substituents and the non-additivities of chemical shifts in aliphatic dichloro esters

1982

Carbon-13 NMR spectra were measured for 25 methyl esters of aliphatic dichlorocarboxylic acids for substituted propanoic to hexanoic acids. Observed 13C shifts are compared with calculated shift values obtained from the shifts of the corresponding monochloro esters by applying a simple sum method. The greatest failures from additivity are observed for αβ and αα substituted carbons. The combined effects of two chlorine substituents were determined, and compared with those obtained from chlorine substituent effects in monochloro esters by assuming additivity. The trends displayed by the combined effects, and also by the non-additivity effects, are discussed.

NMR Spectra of Anilines

2009

1 Introduction 2 Ring and N-Substituted Anilines 3 Multinuclear NMR Studies of p-F-Aniline Derivatives 4 Dynamic NMR of Aniline Derivatives 5 Anilines with Other (Fused) Aromatic Rings 6 NMR Relaxation Studies of Aniline Derivatives 7 Solid State NMR Studies 8 Theoretical Calculations of Aniline NMR Parameters Keywords: aniline NMR spectra; aniline (aminobenzene, phenylamine); ring and N-substituted anilines; dual-substituent-parameter (DSP) analysis; cyclic amine structures; dynamic NMR of aniline derivatives; H NMR spectroscopy as measure of donor strengths; aniline derivative NMR relaxation studies

ChemInform Abstract: 4-Fluoroanilines: Synthesis and Decomposition.

2010

Abstract Fourteen N- and/or 2-substituted 4-fluoroanilines were prepared (the series includes N–C2-bridged compounds). Some of them were found to be thermally unstable when dissolved in chloroform. Both 19 F NMR spectra and comparison of GIAO-DFT calculated and experimental 13 C chemical shifts were used to suggest decomposition products of 4-fluoroanilines.

1971

The polymerisation of ethylene was carried out in the presence of (C5H5)2TiCl2/(C2H5)2AlCl in benzene (I) and of TiCl4/(C2H5)AlCl2 in chlorobenzene (II). In the initial state of the polymerisation with I oligomers with a narrow molecular weight distribution are formed. According to their IR and NMR spectra they were identified as predominantly saturated linear hydrocarbons. The effect of a substitution of the cyclopentadienyl rings by R = CH3 and C2H5 was studied as well as the influence of aging particularly on the molecular weight distribution. The catalytic system II yields predominantly unsaturated branched oligomers with broad molecular weight distribution. The ligand effect on the str…