Structure of initial and ultimate chain units of polydienes obtained with rare-earth catalysts as revealed by H nuclear magnetic resonance spectroscopy

The structure of initial and ultimate chain units in polybutadiene and polyisoprene was studied by means of ²H nuclear magnetic resonance spectroscopy. Polydienes were prepared with a neodymium catalyst; quenching was performed with deuteromethanol. The enrichment of quenched ultimate units by trans-1,4 structures at the expense of cis-1,4 structures at high polymer yields was observed. When using diisobutylaluminium deuteride DAl(i-Bu)₂, as chain transfer agent, it was shown that the principal site of chain transfer reaction was the Al-D bond. The initial unit of polybutadiene was predominantly of trans-1,4 structure.     

红外和核磁共振法鉴定聚醚型聚酯的组成结构

利用红外吸收光谱及核磁共振波谱仪的一维和二维技术对一种未知聚合物试样进行鉴定。由核磁共振二维技术分析得出聚醚酯的序列结构及其分布。结果表明:该未知聚合物试样为聚醚酯弹性体,由对苯二甲酸、间苯二甲酸、新戊二醇、乙二醇、聚四氢呋喃醚共聚而成。     

FTIR和^13C—NMR研究球笼烯钕系聚丁二烯链结构

用ＦＴＩＲ和１３Ｃ－ＮＭＲ法测定了Ｎｄ（ｎａｐｈ）３－Ａｌ（ｉ－Ｂｕ）３－Ｃ６０衍生物催化体系及添加Ｃ６０合成的聚丁二烯的链节含量。结果表明,球笼烯钕系聚丁二烯的顺－１,４链节达９８．８％,反－１,４链节为０．８％;当添加的Ｃ６０用量为Ｃ６０／Ｂｄ＝１．６×１０－４（摩尔比）时,顺－１,４链节降至９３．６％,反－１,４链节升至４．６％,反－１,４链节ＩＲ特征吸收峰较普通钕系聚丁二烯向高频移动了６ｃｍ－１,这表明Ｃ６０分子与Ｂｄ共同参与了向活性中心竞争配位过程。     

Enzyme-catalyzed polymerization of 8-hydroxyquinoline-5-sulfonate by in situ nuclear magnetic resonance spectroscopy

In this report, we describe the use of in situ NMR spectroscopy to elucidate the mechanism of horseradish peroxidase-catalyzed oxidative free-radical coupling of phenols. We demonstrate the potential of the technique for the polymerization of 8-hydroxyquinoline-5-sulfonate (HQS). Based on the structural changes, we establish the involvement of ortho- and para-position protons (to the hydroxyl group) in the oxidative free-radical coupling polymerization with their relative preferences. For example, in HQS, we establish that the positions 2, 4, and 7 are involved in the chemical bonding with the order of preference being 7 ≥ 2 > 4. Analyses of ¹³C-NMR data suggest the formation of C—C- and C—O—C-type coupling bonds during enzymatic polymerization. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1257–1264, 1998     

Isotope-specific analysis of neutron-irradiated lithium aluminate ceramics by nuclear magnetic resonance spectroscopy

The effects of neutron irradiation on lithium aluminate ceramics and the transport and incorporation of tritium into surrounding components are primary concerns in the development of materials for use in tritium production. The high specific activity and volatility of the tritium in activated samples greatly increase the challenges of experimental analysis. This paper reports the determination of structural forms and concentrations of ³H and ⁶Li in irradiated and nonirradiated LiAlO₂ by nuclear magnetic resonance spectroscopy. The experiments find tritium uniformly distributed in hydroxyl groups bridging aluminum centers and lithium in four- and six-coordinated sites. These results demonstrate that measurements can be performed in a nondestructive, safe manner to obtain isotope-selective, quantitative information even on highly hazardous materials.     

C nuclear magnetic resonance spectral analysis of stereosequences in ethylene-propylene copolymer

A number of split peaks dependent on both comonomer sequences and stereosequences were observed in the ¹³C nuclear magnetic resonance (n.m.r.) spectrum of ethylene-propylene (E-P) copolymer. The ¹³C chemical shifts of methylene carbon in stereoisomers of the respective hexad comonomer sequences were predicted by a chemical-shift calculation using the gamma effect on ¹³C chemical shifts and Mark's rotational isomeric state model for E-P copolymer. Assignments of the split peaks that arise from different hexad stereosequences were given by comparison between the observed and calculated chemical shifts. Reference was made to the hexad assignments of comonomer-sequence-dependent peak splittings determined in our previous calculation of ¹³C n.m.r. chemical shifts of stereoregular E-P copolymers. The tacticities were estimated for successive (not separated by ethylene units) propylene units in the hexad sequences.     

Quantitative assessment of alkyl chain branching in alcohol-based surfactants by nuclear magnetic resonance

Surfactants with branched hydrophobes have gained considerable interest, since these can be used in formulations for laundry cleaning at a wide range of conditions. The claims range from improved dissolution rate to hardness tolerance and stain removing efficacy. In contrast to the historically known heavily branched surfactants, novel branched surfactants are less compromised by increased biodegradability. These properties find their basis in the structural characteristics of the hydrophobe, such as number, position, and type of alkyl chain branches. Our current understanding of structure-property relations, however, is hampered by the lack of generic methodology needed to obtain structural data on hydrophobe branching. A nuclear magnetic resonance (NMR) approach was developed by which we could obtain a comprehensive set of quantitative hydrophobe branching parameters in alcoholbased surfactants. The ¹³C and ¹H NMR spin systems of hydrophobe branched species were assigned by means of twodimensional NMR techniques. These assignments allowed the quantitative assessment of these branched species by straight-forward signal integration in the ¹H and ¹³C NMR spectra. The quantified NMR data can be used to understand product performance and the biodegradation of surfactants with branched hydrophobes.     

核磁共振法测定涤纶长丝含油率

采用核磁共振仪测试涤纶长丝含油率,初步探讨了其在生产过程中的应用。结果表明:与传统洗涤法相比,核磁共振法具有快速、简便、试样不需制备、不称重、不需溶剂的优点,且测试精密度和准确度高。     

Hydrogenation of low‐molar‐mass,OH‐telechelic polybutadienes. II. Nuclear magnetic resonance and infrared spectrometric determination of hydroxyl end groups before and after hydrogenation by diimide

¹H nuclear magnetic resonance (¹H‐NMR), ¹³C‐NMR, and infrared spectroscopies were used to determine concentrations (c_OH, in mmol/g) of the secondary hydroxyl end groups in the low‐molar‐mass, OH‐telechelic polybutadienes, and their hydrogenated analogs. Mean OH‐functionality (f_OH ≤ 2), that is, an average number of OH groups per one polymer chain, was calculated from c_OH for each sample and each method, and the results were compared with those obtained by a conventional acetic anhydride titration method. It has been found that with molar masses of the samples studied (2310 to 3410 g/mol), the differences between individual spectrometric methods are usually not higher than approximately 10%, which corresponds to an expected relative experimental error. Certain differences in f_OH between individual methods are discussed. No systematic change of f_OH after virtually total hydrogenation of the olefinic double bonds of the polymeric substrate by diimide was observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3214–3224, 1999     

Monitoring a progressing transesterification reaction by fiber-optic near infrared spectroscopy with correlation to 1H nuclear magnetic resonance spectroscopy

Biodiesel is a promising alternative diesel fuel obtained from vegetable oils, animal fats, or waste oils by transesterifying the oil or fat with an alcohol such as methanol. In an extension of previous work, fiber-optic near infrared spectroscopy was used to quantitatively monitor the transesterification reaction (6-L scale) of a vegetable oil (soybean oil) to methyl soyate. The results were correlated with ¹H nuclear magnetic resonance spectroscopy. The method described here can be applied to the transesterification of other vegetable oils.     

Determining the blend level of mixtures of biodiesel with conventional diesel fuel by fiber-optic near-infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy

Biodiesel, defined as the alkyl esters (usually methyl esters) of vegetable oils, is miscible with conventional diesel fuel at all blend levels. Until the present time, no rapid and reliable analytical method has existed for determining the blend level of biodiesel in conventional diesel fuel. In the present work, near-infrared (NIR) and nuclear magnetic resonance (NMR) spectroscopies were used to determine the blend level of biodiesel in conventional diesel fuel. Several regions in the NIR region (around 6005 cm⁻¹ and 4800–4600 cm⁻¹) are suitable for this purpose. The method is rapid and easy to use, and does not require any hardware changes when using the same instrument for monitoring the biodiesel-producing transesterification reaction and determining biodiesel fuel quality. In ¹H NMR spectroscopy, the integration values of the peaks of the methyl ester moiety and the aliphatic hydrocarbon protons in biodiesel and conventional diesel fuel were used for determining blend levels. The results of NIR and NMR blend level determinations are in good agreement.     

The study of natural epoxy oils and epoxidized vegetable oils by13C nuclear magnetic resonance spectroscopy

The¹³C nuclear magnetic resonance spectra ofVernonia galamensis seed oil and of epoxidized palm super olein, soybean oil and linseed oil have been recorded and interpreted. The chemical shifts of the major signals are assigned and semi-quantitative results are derived. The spectroscopic procedure provides a useful method of analyzing oils that contain epoxy acids. The epoxide function differs from a double bond in its influence on the chemical shifts of nearby carbon atoms.     

Conifer seed oils: Distribution of Δ5 acids between α and β chains by13C nuclear magnetic resonance spectroscopy

Nine seed oils from three different conifer families, already examined by gas chromatography and known to contain diene, triene, and tetraene C₁₈ and C₂₀Δ5 acids, have been reexamined by high-resolution¹³C nuclear magnetic resonance spectroscopy. The Δ5 acids are apparent only in the α-chains. This location is independent of chainlength, double-bond number, and the species considered and is probably a general factor of conifer seed oils. The spectra confirm the presence of oleic, linoleic, α-linolenic, and of Δ5 acids and give quantitative information about (total) n-6, n-3, and Δ5 acids that is in accord with that obtained by gas chromatography.     

The composition of hydrogenated fats by high-resolution13C nuclear magnetic resonance spectroscopy

The high-resolution¹³C nuclear magnetic resonance spectra of twelve hydrogenated fats have been examined. Each spectrum contains 50–100 signals and reveals much about the nature of the acyl chains of both double-bond position and configuration. The signals for the ω1, ω2 and ω3 carbon atoms give information on thecis andtrans isomers of the Δ15, Δ14, Δ13 and Δ12 18:1 esters, respectively. Allylic signals distinguish betweencis andtrans esters, and the proportion of totalcis to totaltrans isomers can be obtained from these. Olefinic signals are the most informative, and most of these have been assigned. This leads to a semi-quantitative estimate of the various 18:1 isomers present. Assignments are based mainly on information already in the literature, but some were confirmed after urea fractionation of the acids from a hydrogenated oil in whichcis andtrans monoene acids were separately concentrated.     

Elaidic acid in rat liver identified by gas chromatography and nuclear magnetic resonance spectroscopy

Fatty acid composition has been commonly determined by gas chromatography (GC). In the most commonly used methods, the lipids must be converted into methyl esters or other derivatives of the fatty acids before being analyzed by GC. Nuclear magnetic resonance (NMR) spectroscopy has become one of the most promising methods to determine organic structures, providing useful data for analyzing the fatty acid composition of edible vegetable oils. The major advantage of NMR is that identification of each fatty acid is carried out by evaluation of particular signals. We report in this work the fatty acid profile of rat liver after consumption of diets containing different concentrations of partially hydrogenated vegetable fat. The fatty acid composition was identified by GC, and trans fatty acids were also identified by ¹³C NMR spectroscopy. The results obtained by the ¹³C NMR method were close enough to those obtained by conventional GC.     

Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy

High-resolution nuclear magnetic resonance (NMR) spectroscopy provides useful data for analyzing fatty acid compositions of edible vegetable oils. Quantitation of each fatty acid was carried out by evaluation of particular peaks. According to the ¹H NMR method, terminal methyl protons, divinyl protons, and allyl protons are useful to calculate linolenic acid, linoleic acid, and oleic acid, respectively. The ω-2 carbon, divinyl carbon, and allylic carbons were used for calculation of these acids by the ¹³C NMR method. Compositional results obtained by NMR coincided well with those of the conventional gas chromatography (GC) method. Results from ¹³C NMR were in better agreement with those from GC than were the results obtained by the ¹H NMR method.     

Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy

High-resolution nuclear magnetic resonance (NMR) spectroscopy provides useful data for analyzing fatty acid compositions of edible vegetable oils. Quantitation of each fatty acid was carried out by evaluation of particular peaks. According to the ¹H NMR method, terminal methyl protons, divinyl protons, and allyl protons are useful to calculate linolenic acid, linoleic acid, and oleic acid, respectively. The ω-2 carbon, divinyl carbon, and allylic carbons were used for calculation of these acids by the ¹³C NMR method. Compositional results obtained by NMR coincided well with those of the conventional gas chromatography (GC) method. Results from ¹³C NMR were in better agreement with those from GC than were the results obtained by the ¹H NMR method.     

Oxidation in fish lipids during thermal stress as studied by 13C nuclear magnetic resonance spectroscopy

¹³C Nuclear magnetic resonance spectroscopy has been applied to elucidate the mechanism of lipid oxidation occurring during thermal treatment of fish. Effects of temperature and time of processing have been studied by means of a model system of lipids, extracted from salmon (Salmo salar) muscle, to simulate industrial conditions of canning. Unsaturated fatty acids located at the sn-2 position of the glycerol moiety were the most prone to oxidative damage. Regarding the mechanism of the reaction, results inferred from olefinic and methylenic resonances indicated a higher susceptibility of the allylic sites closest to the carbonyl group, followed by those placed near the methyl terminal group. Unsaturations located in the middle of the carbon chain did not show much damage. The glyceryl region provided an unusual resonance at 53.4 ppm, which could be assigned to a hydroxylic compound formed during process.     

Nuclear magnetic resonance spectroscopy and reversed-phase high-performance liquid chromatography of peracetylated digalactosyldiacylglycerols

A simple method for the peracetylation of digalactosyldiacylglycerols is described. The peracetylated compounds were isolated by thin-layer chromatography and subjected to nuclear magnetic resonance spectroscopy for structure elucidation. The proton signals at acetylated sites are shifted downfield compared to the nonderivatized compounds, resulting in improved resolution. The peracetylated compounds were also subjected to molecular species analysis by reversed-phase high-performance liquid chromatography. The chromatography behavior of the peracetylated compounds was similar to that of triacylglycerols, displaying narrow and symmetrical peaks yielding a highly resolved molecular species profile.     

Radiation degradation of epoxidized natural rubber studied by solid‐state nuclear magnetic resonance and infrared spectroscopy

The mechanism of radiation‐induced structural changes in epoxidized natural rubber was investigated using nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. Samples were irradiated both under vacuum and in air. Because the rubbers crosslinked during irradiation, solid‐state NMR had to be used. The cross polarized/magic angle spinning NMR spectra were used to calculate the radiation yields. Ring opening of the epoxy groups was found to occur during irradiation. Most of the crosslinking was due to epoxy group ring opening, and very little or no C C crosslinking was observed. © 2000 Society of Chemical Industry