Deuterated Samples Research Articles

ChemInform Abstract: Determination of Dipole‐Dipole Couplings in Oriented n‐Hexane by Two‐Dimensional NMR

We give here a preliminary report of a method to analyze spectra and determine structures of molecules dissolved in liquid crystals. The basic idea is the use of randomly deuterated samples (a synthetically facile undertaking) which contain a mixture of all possible isotopomers of a molecule. This approach has been used before in the analysis of some cyclic compounds in nematic liquid crystals. A highly deuterated sample will contain mostly isotopomers with just a few protons. Thus, the task of interpreting one complex spectrum is reduced to one of analyzing a large number of simple but overlapping spectra. The crucial point is the ability to recognize the individual signals which derive from the same spin system (arise from one isotopomer). This can be achieved by the combined application of two-dimensional NMR and multiple-quantum NMR techniques as is shown for the case of n-hexane.

Determination of dipole-dipole couplings in oriented n-hexane by two-dimensional NMR

We give here a preliminary report of a method to analyze spectra and determine structures of molecules dissolved in liquid crystals. The basic idea is the use of randomly deuterated samples (a synthetically facile undertaking) which contain a mixture of all possible isotopomers of a molecule. This approach has been used before in the analysis of some cyclic compounds in nematic liquid crystals. A highly deuterated sample will contain mostly isotopomers with just a few protons. Thus, the task of interpreting one complex spectrum is reduced to one of analyzing a large number of simple but overlapping spectra. The crucial point is the ability to recognize the individual signals which derive from the same spin system (arise from one isotopomer). This can be achieved by the combined application of two-dimensional NMR and multiple-quantum NMR techniques as is shown for the case of n-hexane.

H2-NMR investigation of the two-dimensional smectic F and I phases

The smectic F and I phases have been reported to be quasi-two dimensional systems. The S F phase was shown to be the first tilted version of the hexatic phase whereas the S i phase was shown to exhibit a 2D solid-like order. We have studied the terephtal-bis(4-n decylaniline) compound (TBDA) in which the S F phase surprisingly occurs at lower temperatures than the S i phase with a higher degree of positional order. To further investigate this puzzling problem we have studied the molecular behaviour by means of H 2 -NMR experiments. Two deuterated samples of TBDA have been prepared so as to allow separate investigations of the aromatic core and end-chain orderings. Concerning the aromatic part the data have been interpreted in a simple model based on the reorientations of the phenyl rings about their para-axis. This analysis suggests a possible scenerio for the intramolecular disordering and its influence on the intermolecular ordering through the smectic F and I phases Etude des relations entre l'ordre structural des phases F et I et le comportement moleculaire dans le TBBA

Infrared Spectra of Jute Fibers at Different Stages of Growth

Infrared spectra of jute fibers at different stages of growth, both at the normal and deuterated conditions, were analyzed. Peak heights at wave bands, which can be ascribed to hemicellulose and lignin, show a maximum around 20-35 days of growth, suggesting maximum formation of these substances around this period. An increase of OD content from the early stage to this period also points to this possibility. Spectra of both undeuterated and deuterated samples suggest that at maturity there is either a fall in the hemicellulose content or there is greater esterification between lignin and carbohydrate.

Wide-Line Proton Magnetic Resonance Studies of Deuterated Poly(γ-benzyl glutamate). Verification of Previous Interpretation for Side Chain Motion

The wide-line proton magnetic resonance of poly(γ-benzyl glutamate) (PBG) was studied using two deuterated samples. One was deuterated at the phenyl groups, PBG-d5, and the other, at the benzyl groups, PBG-d7. The temperature dependence of the line width and the second moment was compared with that for PBG. It was found that the use of these deuterated samples made it possible to identify the particular part of the side chain participating in the molecular motion. The results indicated that in PBG, the side chain motion is excited first at the end group and then propagates to the backbone with rise in temperature, in agreement with our previous interpretation. An attempt was made to decompose the second moment of PBG into several components.

Formula omitted] and [formula omitted] nuclear quadrupole double-resonance study of several hydroxide compounds. II. The water molecule

Using the technique of double resonance with coupled multiplets at 77 K and room temperature, 17O double-resonance signals were detected from the H 2O molecules in a number of hydrates of the alkali metal and alkaline earth metal hydroxides at natural abundance. The deuteron double-resonance signals were measured in deuterated samples at 77 K using double resonance by level crossing. The correlations between the 17O and 2H quadrupole coupling constants and the hydrogen bond strength are discussed. The 17O DRCM results for BeSO 4 · 4H 2O are included.

Formula omitted] and [formula omitted] nuclear quadrupole double-resonance study of an oxonium ion in H 2SO 4 · H 2O

Using the technique of high-sensitivity double resonance with coupled multiplets (DRCM) at 77 K, a 17O 1H dipolar fine structure was revealed for two 17O sites in H 2SO 4 · H 2O at natural abundance. The lines are assigned to H 30 + and the SOH group in HSO 4 −. To the former, the theoretical DRCM spectra fit well with the 17O maximum electric field gradient component, V zz , along a C 3 v axis and the symmetrical geometry of H30+ ion with R(OH) = 1.03 Å, R(H…H) = 1.72 Å, and HÔH angle of 113.5° indicating a slight flattening of a pyramidal ion. The 170 quadrupole coupling parameters obtained as e 2qQ h = +7513 kHz and η = 0.104 for the 17O nucleus in the tetrahedral environment of a H 30 + ion are shown to be consistent with the predictions based on a Townes and Dailey model. The 2H quadrupole double-resonance spectrum of 20% deuterated sample was measured, yielding four inequivalent 2H sites, but, for highly deuterated samples, these spectra are complicated by a strong isotope effect.

TGA-DTA, infrared and x-ray powder diffraction studies on strontium nitroprusside and its hydrates

Dehydration data for the tetra-, di- and monohydrate of strontium nitroprusside and the vibrational behaviour of the water molecules in normal and deuterated samples agree with crystal data previously reported (for the di- and tetrahydrate as single crystals) and in this paper (monohydrate as a powder). Four distinct types of water molecules are present in the three hydrates with one type (oxygen bonded to Sr 2+) in common. Other types are a non hydrogen-bonded molecule (dihydrate), a molecule bonded by a single hydrogen atom to the nitrogen atom of a cyanide group and a set of two molecules similarly bonded to the oxygen atom of the previous type (tetrahydrate). The spatial orientation of the NO groups of the nitroprusside ions in the tetrahydrate is confirmed by the observed dichroism of the corresponding stretching band.

Conformation of oxytocin studied by laser Raman spectroscopy

The peptide backbone conformation and salient structural details of oxytocin were examined by laser Raman spectroscopy. Spectra were obtained in the solid phase, water, 2H 2O, and dimethyl sulfoxide solutions. A distinct Amide I band was obtained at 1663 cm −1 for aqueous and deuterated samples and 1666 cm −1 for the solid sample. A relatively high frequency Amide III band at 1260 cm −1 was obtained. It is concluded that these Amide I and III bands arise from the “β-turn”-like conformation of oxytocin. The tyrosine side chain, according to the I 850 cm −1 / I 830cm −1 intensity ratio, is exposed to the solvent. The S-S stretching vibration at 512 cm −1 indicates the conformation of C-C-S-S-C-C in the disulfide bridge of oxytocin in the ring is gauche-gauche-gauche.

The vibrational analysis of 1,1-dimethylcyclopropane and 1,1-dimethyl-d 6-cyclopropane

The i.r. and Raman spectra of 1,1-dimethylcyclopropane and 1,1-dimethyl-d 6-Cyclopropane have been investigated from 100 to 4000 cm −1. Infrared spectra are reported in the solid and vapor states and Raman spectra are reported for all three physical states. Data from the normal and deuterated samples were used for Teller—Redlich product rule calculations as a check on correctness of the vibrational assignments. The 1 ← 0 and 2 ← 0 torsional transitions were observed and the calculated barriers to internal rotation for the solid and vapor states are 3.7 and 3.2 kcal/mole respectively.

14N nuclear quadrupole coupling constants in imidazole

All six 14N nuclear quadrupole resonances in imidazole were observed. Using deuterated samples, the EQR of the deuterium in ▪ bond and the first unambiguous identification of the quadrupole coupling constants at a bi-coordinate N site were obtained.

Structure and physical properties of aluminium alkoxides: 1. Mass spectra of aluminium isopropoxides

AbstractThe mass spectrum of aluminium isopropoxide has been investigated using an AEI‐MS 9 mass spectrometer.The results indicate that the vapour of the solid consists largely of tetramer species; dimer and trimer are possibly present also in minor quantities.Probable fragmentation schemes are deduced from comparison of mass spectra of unlabelled and deuterated samples (deuterated at the secondary carbon atom of the isopropyl group). The tetramer molecular ion loses an isopropoxy radical or, successively, a methyl radical and a molecule of acetaldehyde, followed by the elimination of di‐isopropyl ether. A mechanism for this reaction is proposed. The further fragmentation may involve the loss of propene, di‐isopropyl ether and/or aluminiumoxide isopropoxide.

VO2+ and X-Ray Produced V2+ in Tutton Salt

The electron spin resonance spectrum of the vanadyl ion (VO2+) in single crystals of Zn (NH4)2(SO4)2·6H2O is studied and the properties of x-ray produced V2+ are compared to those of the V2+ grown directly into the same host lattice. In the unirradiated samples the V–O axis is found to have three possible orientations with populations in the ratio 20:5:1. For the most populous position the spin Hamiltonian parameters at X band are S=½, gx=1.9813, gy=1.9801, gz=1.9331, Ax=0.007120/cm, Ay=0.007244/cm, Az=0.018281/cm, and Q′=7×10—5/cm with the x, y principal axes of the g and A tensor being displaced from each other by 23°20′. Furthermore, the vanadyl hyperfine lines show an additional anisotropic structure of five lines, absent in deuterated samples. The parameters for V2+ at K band in both the as-grown and irradiated crystals are S=3/2, gz=1.9717, gy=1.9733, D=—0.15613/cm, E=—0.02280/cm, and A=—0.00825/cm. A study of the effect of x-ray dose upon the line intensity is made. An impurity model of a vanadyl pentahydrate complex associated with a water moleculy vacancy is proposed.