Determination of configurational isomers in polybutadienes by <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR spectroscopy

The NMR spectra (600 MHz) of polybutadienes containing different amounts of cis-1,4, trans- 1,4 and 1,2 units are analyzed. The critical consideration of signal assignment and the comparison of ¹H and ¹³C NMR data reveal that there are significant limitations to the quantitative characterization of polybutadienes with the use of NMR spectroscopy.     

Structure of Galactomannans from <Emphasis Type="Italic">Gleditsia delavayi</Emphasis> and <Emphasis Type="Italic">G. aquatica</Emphasis> by <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR Spectroscopy

The structure of galactomannans isolated from seeds of G. delavayi and G. aquatica was studied by ¹H and ¹³C NMR spectroscopy. It was found that the galactomannans consisted mainly of β-1-4-bound mannopyranoses, a part of which was substituted on the C-6 hydroxyl by terminal units of α-galactopyranose.__________Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 12–13, January–February, 2005.     

Long-range <Superscript>19</Superscript>F-<Superscript>1</Superscript>H spin-spin coupling as an indication of conformational equilibrium of fluoro-substituted aryl vinyl sulfides

Long-range ¹⁹F-¹H spin-spin coupling with participation of vinyl group protons, observed in the ¹H NMR spectra of fluoro-substituted aryl vinyl sulfides, indicates that these compounds exist as equilibrium mixtures of s-cis and s-trans rotational isomers.     

Through space spin-spin coupling <Superscript>19</Superscript>F-<Superscript>1</Superscript>H as the base for comparative analysis of conformational equilibrium in fluorine-substituted aryl vinyl selenides and sulfides

The analysis of long-range spin-spin coupling ¹⁹F-¹H and the other conformation-dependent parameters of ¹H NMR spectra shows that aryl vinyl selenides like aryl vinyl sulfides exist as mixtures of s-cis and s-trans rotational isomers. The combined data of ¹H and ¹³C NMR spectra reveal the increase in the torsional angle ϑ at the bond X-CH=CH₂ (X = S, Se) in selenides compared to sulfides due to diminished interaction energy of the unshared electron pairs of selenium with the π*-orbitals of the double bond as compared to analogous interaction in sulfides.     

Quantitative <Superscript>2</Superscript>H NMR spectroscopy

The selectivity of deuterium distribution between the nonequivalent positions in 3-carene (1), 4-α-acetyl-2-carene (2), and 4-(1-hydroxyethyl)-2-carene (3) has been measured by ²H-{¹H} NMR spectroscopy at the natural abundance of deuterium. These “H/D-isotope portraits” were shown to be typical of terpenes and terpenoids produced in plants via the biosynthetic DXP pathway. The mechanism of acylation of 1 was studied by the density functional theory method (PBE functional, TZ2p basis set). The six-membered ring in compound 1 is planar. However, the endo attack of electrophiles on this ring is more favorable both kinetically and thermodynamically. It was shown both experimentally and theoretically that the elimination of a hydrogen atom in the second reaction step proceeds stereoselectively at the C(2) atom from the anti position with respect to the three-membered ring and occurs with pronounced nucleophilic assistance from the carbonyl group. For Part 2, see Ref. 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1657–1664, August, 2008.     

Potential and Limitations of 2D <Superscript>1</Superscript>H–<Superscript>1</Superscript>H Spin-Exchange CRAMPS Experiments to Characterize Structures of Organic Solids

Summary.  A brief overview of our recent results concerning the application of 2D CRAMPS experiments to investigate a wide range of materials is presented. The abilities of the 2D ¹H–¹H spin-exchange technique to characterize the structure of organic solids as well as the limitations resulting from segmental mobility and from undesired coherence transfer are discussed. Basic principles of ¹H NMR line-narrowing and procedures for analysis of the spin-exchange process are introduced. We focused to the qualitative and quantitative analysis of complex spin-exchange process leading to the determination of domain sizes and morphology in heterogeneous multicomponent systems as well as the characterization of clustering of surface hydroxyl groups in polysiloxane networks. Particular attention is devoted to the determination of the ¹H–¹H interatomic distances in the presence of local molecular motion. Finally we discuss limitations of the ¹³C–¹³C correlation mediated by ¹H–¹H spin exchange to obtain structural constraints. The application of Lee-Goldburg cross-polarization to suppress undesired coherence transfer is proposed. Corresponding author. E-mail: brus@imc.cas.cz Received May 28, 2002; accepted (revised) July 1, 2002     

Quantification of chondroitin sulfate and dermatan sulfate in danaparoid sodium by <Superscript>1</Superscript>H NMR spectroscopy and PLS regression

Danaparoid sodium (the active pharmaceutical ingredient in Orgaran; Merck Sharp and Dohme) is a biopolymeric non-heparin drug used as anticoagulant and antithrombotic agent approved for the prophylaxis of post-operative deep-vein thrombosis, which may lead to pulmonary embolism in patients undergoing, e.g., elective hip replacement surgery. It consists of a mixture of three glycosaminoglycans (GAGs): heparan sulfate (HS), dermatan sulfate (DS), and chondroitin sulfate (CS). Currently, the CS and DS content are quantified by means of a time-consuming enzymatic method. In this paper the use of ¹H NMR in combination with multivariate regression (partial least-squares, PLS) is proposed as a new method. In order to evaluate the proposed method, a series of danaparoid sodium samples were analyzed and the results were compared with those obtained by the enzymatic method (reference method). The results showed that the proposed ¹H NMR method is a good alternative for analysis of CS and DS in danaparoid sodium. Accuracy of ±0.7% (w/w) and ±1.1% (w/w) for CS and DS was obtained by the ¹H NMR method and accuracy of ±1.0% (w/w) and ±1.3% (w/w) by the enzymatic method. Furthermore, the use of ¹H NMR in combination with PLS results in a fast quantification. The analysis time is reduced to 35 min per sample instead of 60 h for a maximum of 16 samples.     

High-Resolution <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR of Glycyrrhizic Acid and Its Esters

Resonances for protons and C atoms in the ¹H and ¹³C NMR spectra of glycyrrhizic acid and its esters were assigned using high-resolution ¹H (600 MHz) and ¹³C (150 MHz) NMR methods. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 347–350, July–August, 2005.     

2-Amino-4-aryl-1-arylideneaminoimidazoles and Acylation Products: A Multinuclear (<Superscript>1</Superscript>H, <Superscript>13</Superscript>C, <Superscript>15</Superscript>N) NMR Study

Summary. The structure of 2-amino-4-aryl-1-arylideneaminoimidazoles in DMSO-d₆ solution was investigated by means of NMR spectroscopic methods (¹H, ¹³C, ¹⁵N). From these data the (E)-configuration at the excocyclic C=N bond and a strong preference for the conformer with the imidazole H-5 and the N=CH proton being spatially close (s-trans regarding the N–N bond) can be concluded. Reaction of the title compounds with acetic anhydride leads to mono and diacylation at the 2-amino group, whereas treatment with pivalic anhydride exclusively affords the corresponding monoacyl product. The mono- and diacylation products exhibit similar configurational and conformational properties as the parent compounds.     

Prototropic processes in benzaurins. <Superscript>19</Superscript>F and <Superscript>1</Superscript>H NMR spectra of fluoro- and methylsubstituted 4-hydroxyphenyl-diphenylcarbinols,related fuchsones and benzaurins

Tautomerism of benzaurins and hydration are studied. ¹H and ¹⁹F chemical shifts have been determined for a number of substituted 4-hydroxyphenyl-diphenyl carbinols containing fluorine in a 3-, 3*- or 4*-position, and for similar compounds containing additional methyl groups in a position of 3, 3** or 4**. The same data have been obtained for the fuchsones prepared by dehydration of the above carbinols. On this basis chemical shifts of fluorine in different positions have been evaluated as a monitor of the transformation of 4-hydroxyphenyl group to the semiquinone moiety. The ¹⁹F NMR can be used to monitor the transformation of 4**-fluorobenzaurin and the related 3,3*-disubstituted and 3,3*,5,5*-tetramethylsubstituted compounds to the corresponding carbinols due to the addition of a water molecule and to study the tautomerism of the two latter benzaurins as well as that of 3,3*,4**trifluorobenzaurin. Furthermore, fluorine and methyl group chemical shifts are sensitive to syn-anti-isomerism in substituted fuchsones.     

Complete <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR signal assignments and chemical shift calculations of four 1,2,4-oxadiazole-based light-emitting liquid crystals

In this article, we describe the complete ¹H and ¹³C NMR signal assignments of four 1,2,4-oxadiazoles possessing light-emitting liquid crystal properties. These results were obtained by using one- and two-dimensional NMR techniques as well as GIAO (PCM) calculations at B3LYP/6-311++G(d,p) level for compounds 1 and 2a–d. The computed values are in good agreement with the ones obtained experimentally. In addition, some previously unexplained thermotropic features of compounds 2a–d could be clarified with the help of the geometry optimization calculations carried out by us.     

A new 9,10-dihydrophenanthrenedione from <Emphasis Type="Italic">Cannabis sativa</Emphasis>

The structure of a new 9,10-dihydrophenanthrenedione, which was isolated from the leaves and branches of Cannabis sativa L., was elucidated as 9,10-dihydro-2,3,5,6-tetramethoxyphenanthrene-1,4-dione (1) on the basis of MS, ¹H NMR, and ¹³C NMR methods, especially 2D NMR techniques (HMBC and NOESY).     

Determination of the molecular weight of polyoxypropylenepolyols by <Superscript>1</Superscript>H NMR spectroscopy

Commercial and laboratory samples of polyoxypropylenepolyols were studied by ¹H NMR spectroscopy at operating frequencies of 100 and 500 MHz. Various methods depending on the solvent used were suggested for determining the equivalent weight (molecular weight of the polyether per terminal hydroxy group). The ¹H NMR data are compared to the data obtained by chemical methods and gel permeation chromatography.     

<Superscript>1</Superscript>H NMR spectra of water contained in solutions of poly(<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone) and its modification products in CDCl<Subscript>3</Subscript>

¹H NMR spectra in CDCl₃ of poly(N-vinylpyrrolidone), epoxidized poly(N-vinyl-pyrrolidone), and products derived from the latter by modification with amino acids (glycine, β-alanine, γ-aminobutyric acid, and ε-aminocaproic acid) were examined. The ¹H NMR spectra of the modified polymers contain signals for water protons due to different centers of water sorption. These signals differ in chemical shift and integral intensity and indicate a changed spatial packing of the polymer as the result of its modification. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2377–2380, October, 2005.     

Hydrogen‐Assisted Unique Incorporation of 1,4‐Divinylbenzene in Copolymerization with Propylene Using an Isospecific Zirconocene Catalyst

Summary: Propylene was copolymerized with 1,4‐divinylbenzene (1,4‐DVB) using rac‐Me₂Si(2‐Me‐4‐Ph‐Ind)₂ZrCl₂ and MAO in the presence of hydrogen. ¹H NMR spectra of the obtained copolymer confirmed the successful incorporation of 1,4‐DVB. ¹³C NMR analysis revealed a unique copolymer structure with the incorporated 1,4‐DVB units predominantly forming 1,4‐substituted phenyl repeating units in the polymer main chain. A plausible mechanism involving spontaneous insertion of terminal styryl into Zr‐H species was proposed to rationalize the unique incorporation of 1,4‐DVB.

Copolymerization of propylene with 1,4‐divinylbenzene in the presence of hydrogen.     

Co<Superscript>II</Superscript> and Rh<Superscript>I</Superscript> complexes with <Emphasis Type="Italic">C</Emphasis><Subscript>2</Subscript>-symmetric chiral diamines of the dioxolane series

The reaction of di-μ-chlorobis(1,5-cyclooctadiene)dirhodium with (4S, 5S)-2,2-dimethyl-4,5-bis(methylaminomethyl)-1,3-dioxolane (1) gave the complex [Rh(cod)(1)]Cl (cod is 1,5-cyclooctadiene). The composition of the complexes CoCl₂ · L₂ and [Rh(cod)(L₂)]X (L₂ = 1, (4S,5S)-2,2-dimethyl-4,5-bis(aminomethyl)-1,3-dioxolane, and (4S, 5S)-2,2-dimethyl-4,5-bis(dimethylaminomethyl)-1,3-dioxolane; X = Cl, TfO) was studied using IR and ¹H NMR spectroscopy. In the Rh^I cyclooctadienediamine complexes, the diene molecule forms a stronger bond with the metal atom than that in the cyclooctadienediphosphine analogs. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2270–2274, October, 2005.     

Study on the structure of epoxidized <Emphasis Type="Italic">trans</Emphasis>-1,4-polyisoprene synthesized by heterogeneous and homogeneous method using <Superscript>13</Superscript>C NMR<Superscript>1</Superscript>

A structure study of epoxidized trans-1,4-polyisoprene (ETPI) synthesized by heterogeneous method is carried out using ¹³C-NMR. In this paper, we present a new analytical method for assigning overlapping ¹³C-NMR signals of ETPI in terms of the triad of trans-1,4-isoprene and epoxidized units. The monomer unit sequence distributions in epoxidized fractions of heterogeneous ETPI are detected and compared with those of ETPI synthesized by homogeneous method. Results prove that in less epoxidized polymer (16%), monomer unit sequence distributions in epoxidized fractions of heterogeneous ETPI are randomly distributed. And when the epoxy content is higher than 23%, a certain degree of block structure appears. What’s more, with the increasing of epoxy content, more block structure appears.     

Hydridosilazanes hydrolysis-condensation reactions studied by <Superscript>1</Superscript>H and <Superscript>29</Superscript>Si liquid NMR spectroscopy

Hydridosilazane compounds containing Si–N and Si–H bonds can be used as precursors of SiO_x materials. The hydrolysis-condensation reactions of tetramethyldisilazane, as a polyhydridosilazane model compound, were investigated by ¹H and ²⁹Si liquid NMR spectroscopy. These reactions were carried out at room temperature for up to 120 min in presence of water. The identified products are short linear siloxane species (hydride terminated polydimethylsiloxanes M^HD_xM^H) and cyclosiloxanes. Silicon hydride persistence in the reactional mixture suggested that silazane group is more sensitive to hydrolysis reaction than silicon hydride group. Moreover, additional experiments evidenced that the low steric hindrance of the silicon hydride influences the silazane hydrolysis kinetic. Hence the presence of ammonia released during silazane hydrolysis reaction was demonstrated to be a catalyst of the silicon hydride hydrolysis reaction.     

<Superscript>1</Superscript>H and <Superscript>7</Superscript>Li NMR in defect cobaltite Li<Subscript>0.6</Subscript>CoO<Subscript>2</Subscript>

Within a temperature range of 120–330 K, ⁷Li NMR spectra in Li_0.6CoO₂ are obtained. It is shown that as the temperature increases, both smooth and stepwise variation of ⁷Li NMR contact shifts occurs. The observed effects are explained by the occupation of the excited levels of cobalt ions. The stepwise change of the resonance line width depending on the temperature is revealed. It is driven by the features of the diffusive motion of lithium ions. The calculation of the ¹H NMR line shape provides the determination of the ratio of one-, two-, and three-spin proton clusters in Li_0.6CoO₂·xH₂O.     

DFT calculations of <Superscript>14</Superscript>N, <Superscript>17</Superscript>O,and <Superscript>2</Superscript>H NQR parameters: Investigation of hydrogen bond interactions in sulfapyridine crystalline structure

DFT calculations of electric field gradient (EFG) tensors at the sites of ¹⁴N, ¹⁷O, and ²H nuclei are carried out to characterize the hydrogen bond (HB) interactions in the sulfapyridine crystal structure. One-molecule (monomer) and hydrogen-bonded hexameric cluster models of sulfapyridine are constructed according to available X-ray coordinates where the proton positions are optimized. Then, EFG tensors are calculated for both monomer and target molecule in the hexameric cluster of sulfapyridine to show the effect of HB interactions on the tensors. The calculated EFG tensors are converted to the experimentally measurable nuclear quadrupole resonance (NQR) parameters: quadrupole coupling constant (C _Q ) and asymmetry parameter (η _Q ). The results reveal different contribution of various nuclei to N-H⋯N and N-H⋯O HB interactions in the cluster where the N2 and O1 have major contributions. The computations are performed with B3LYP and B3PW91 functionals DFT method and 6-311+G* and 6-311++G** standard basis sets using the Gaussian 98 package.