Determination of Compositional,Configurational Sequences in High Conversion Methyl Methacrylate-Methacrylic Acid Emulsion Copolymers Using a Rapid and Selective Counting Procedure

High conversion methyl methacrylate (MMA)-methacrylic acid (MA) copolymers prepared by two different emulsion polymerization processes were characterized in terms of composition and sequence distribution by ¹H- and ¹³C-NMR, taking into account the conversion effect. A rapid and selective counting procedure for calculating the compositional configurational pentads (512 values) in these copolymers is described. From this counting procedure and using the Klesper's assignment of the 18 peaks observed in the ¹³C-NMR carbonyl resonance spectrum of the copolymers, a relatively good agreement was found between the calculated and experimental fractions of each peak intensity. Moreover, this study allows differences in compositional homogeneity to be characterized as a function of the nature of the emulsion polymerization process.     

Use of13C chemical shift/charge density linear relationship for ranking chemical structures

A novel approach to molecular structure elucidation based on ranking chemical structures in agreement with the¹³C NMR chemical shift/charge density linear relationship is suggested. The structure having the lowest standard approximation error (SAE) is considered to be the correct one. Each ranked structure is additionally tested for the¹³C chemical shift equivalence corresponding to its constitutional symmetry (in terms of the charge densities).This paper is Part VI of the series Automatic assignment of¹³C NMR signals. For Part V see ref. [1].     

Expert system for solving problems in carbon-13 nuclear magnetic resonance spectroscopy

The expert system CARBON is built around a knowledge base consisting of spectra/structure correlations, tables of data, mathematical formulae and graph-theory procedures and on a data base of 2500 assigned ¹³C-NMR spectra. The built-in knowledge enables the user to obtain suggestions for solutions to problems of different types arising in ¹³C-NMR spectroscopy. Use of the system is facilitated by appropriate command files, large on-line help files, and user-friendly dialogue. The system can be used with spectrometries other than ¹³C-NMR and in other fields concerned with correlations between chemical structures and properties.     

Melamine–formaldehyde resins: Constitutional characterization by fourier transform 13C-NMR spectroscopy

The random chemical structures of melamine–formaldehyde resins, including methylated melamine–formaldehyde resins and urea–melamine formaldehyde resins, were investigated by ¹³C-NMR spectroscopy (Fourier transform). All the combined formaldehydes, methylol and methyl ether groups, methylene structures, and dimethylene ether structures were assigned. A ¹³C chemical shift of methylene carbon occurred by substitution of other constituents of the methylene group for a proton of the adjacent monosubstituted nitrogen atom, as shown in a ¹³C-NMR spectrum of urea–formaldehyde resins. It was found that the chemical shift of each corresponding carbon of both melamine resins and urea–melamine resins was almost superimposed with that of urea resins.     

A study of the ring size in the copolymer of divinyl ether and maleic anhydride by H-NMR spectroscopy

The well-known alternating 1:2 cyclocopolymer of divinyl ether (DVE) and maleic anhydride (MA) possesses a wide spectrum of biological activities, including antitumor. Recent research on the structure of a variety of cyclopolymers has raised a question about the ring size of this cyclocopolymer. In this article we report on an extensive spectroscopic study of its structure. By use of deuterated monomers the H-NMR peaks at δ 2.31, 3.47, 4.06, and 4.49 ppm with an area ratio of 2:1:1:1 were assigned to the hydrogens of methylenes, methines on the backbone anhydride unit, methines on the ring anhydride unit, and methines adjacent to oxygen on the cyclic ether ring, respectively. By examination of the possible isomeric structures of the bicyclic ring, the splitting of each peak group was further assigned for cis and trans disubstitutions on the anhydride unit. The splitting pattern from the 300-MHz NMR spectrum of the DVE-2,3-dideuteriomaleic anhydride (DMA) copolymer confirmed the unsymmetrical ring structure. ¹³C-NMR spectra were consistent with the conclusion from the H-NMR spectra. A chair-form, six-membered ring with predominantly trans geometry in the anhydride ring was assigned to the structure of DVE–MA copolymer. On the basis of little or no change in the ¹³C-NMR spectra of the copolymers prepared at different temperatures it was concluded that there was no significant change in structure with temperature. This led to the assignment of the energetically favored, six-membered ring structure to the copolymer prepared under these conditions. A mechanism for cyclocopolymerization, based on the HOMO–LUMO interaction of the comonomers and the intramolecular radical addition on the preoriented double bond, was proposed. This mechanism leads to the formation of the six-membered ring structure of the copolymer as the only product. A ¹³C-NMR study of the structure of the copolymer prepared in chloroform by Kunitake and Tsukino is being published as a companion article.     

NMR studies of viomycin

The ¹H and ¹³C NMR spectra of antibiotic Viomycin sulphate and its constituent aminoacids in H₂O and D₂O were examined in a wide range of pH values. The spectra were analysed by proton spin-spin decoupling experiments and measurements of the relative intensities of the resonance and chemical shift values. Exchange experiments were also carried out and an almost complete assignment of the resonances of the spectra was possible. The data obtained are discussed in terms of possible structures for Viomycin and the presence of intramolecular hydrogen bonds. Some information about the conformation of the molecule is also given. A tentative assignment of the ¹³C spectrum of Viomycin is given and the experimental ¹³C chemical shift values compare well with the theoretical ones evaluated by Grant's rule.     

Characterization of plasma polymers from tetramethylsilane,octamethylcyclotetrasiloxane, and methyltrimethoxysilane

The products in inductively coupled plasma excited in organosilicic compounds were studied on chemical structures by spectroscopic methods. Plasma-polymerized tetramethylsilane (PA) contains not only Si? CH₃ groups but also Si? H groups on IR and ²⁹Si-NMR analyses. ¹³C-NMR spectrum of PA reveals that the crosslinked structure of PA is mainly constructed of Ch₂ and CH groups. Plasma-polymerized octamethyleyclotetrasiloxane (PD₄) is composed of Si? CH₃ and Si? O groups. ¹³C- and ²⁹Si-NMR spectra of PD₄ point out the highly preservation of the structural units similar to the monomer. These data of PD₄ suggest that PD₄ is formed from the ring-opening polymerization by cleavages of Si? O bonds. ¹³C-NMR spectrum of poly[methyltrimethoxysilane] (PT) indicates the existence of CH₃? O groups, meanwhile its ²⁹Si-NMR analysis concludes that PT is chiefly composed of the structural units similar to the monomer. The surface analyses by XPS of PA, PD₄ and PT suggest that these organosilicic plasma polymers resemble their starting materials.     

~(13)C-NMR研究聚丁二烯的序列结构

本文采用~13C-NMR方法研究了不同催化体系制备的聚丁二烯。经分析指出,聚丁二烯分子链的三种序列(顺-1,4-序列、反-1,4-序列和1,2-序列)和十七类脂碳碳核为~13C-NNR谱贡献了十六个谱峰。经数据的解析,得到一组计算聚丁二烯脂碳部分各谱峰化学位移的经验参数。在本文条件下,应用该组参数得到的计算值与实验值符合较好。本文确认了聚丁二烯反-1,4-序列第四峰(T_4)的存在。初步研究了聚丁二烯~13℃-NMR谱图的定量处理问题。     

Qualitative and quantitative characterization of a complex mixture of hexylbenzenes by 13C nuclear magnetic resonance and gas chromatography-mass spectrometry

Summary A considerable amount of byproducts is formed in the production of isopropylbenzene (cumene). Recently, a distillation fraction of these byproducts became commercially attractive which justified its compositional analysis. All the signals in the complex ¹³C nuclear magnetic resonance (NMR) spectrum of this material have been assigned. The mass spectra of the individual constituents were recorded by the application of capillary gas chromatography-mass spectrometry. The data obtained with both analytical techniques revealed that the product is composed of a complex mixture of 3 isomeric diisopropylbenzenes and 10 different hexyl-substituted benzenes. The mass spectra and carbon-13 NMR chemical shift data of most of the compounds presented here have not been previously reported. NMR data of all possible butyl- and a number of pentyl-substituted benzenes are included in this report for assignment purposes. Quantitative studies on this material and some of its distillation fractions by ¹³C NMR and gas chromatography enabled the assignment of individual peaks in the gas chromatogram.

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Qualitative und quantitative Charakterisierung eines komplexen Gemisches von Hexylbenzolen durch ¹³C-NMR und GC/MS

     

Characterization of mechanically sheared ethylene–propylene copolymers by high resolution NMR

We report high-resolution solution-state NMR experiments on chain ends generated in ethylene–propylene copolymers by mechanical shearing in an extruder. The use of the higher resolution of the ¹³C-NMR spectrum, in a two-dimensional ¹H-¹³C chemical shift correlation experiment, has allowed the complete resolution and assignment of the olefinic chain-end region of the ¹H-NMR spectrum. Simultaneously, the assignments of the ¹³C olefinic resonances, previously identified [A. C. Kolbert, J. G. Didier, and L. Xu, Macromolecules, 29 , 8591 (1996)] are confirmed. An iterative method for calculating the average molecular weight, based on quantitative measurements of the olefinic ¹H-NMR peak intensities is introduced and these results are compared with measurements from ¹³C-NMR and size exclusion chromatography and correlated to reduced viscosities. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1955–1961, 1997     

Chemistry of the phenoxathiins and isosterically related heterocycles. IX.N-oxidation on the 13C-nmr chemical shifts and coupling constants of the 1-azaphenoxathiin system

The synthesis of 1-azaphenoxathiin N-oxide is described. Total assignment of the ¹³C-nmr spectrum and the effects of the N-oxide moiety on the chemical shifts and ¹H-¹³C spin couplings constants are described and compared to the parent 1-azaphenoxathiin system. The potential for the use of N-oxidation induced changes in ¹³C-nmr chemical shifts and ¹H-¹³C coupling constants as an assignment criterion is also discussed.     

13C-NMR spectroscopy study of polyurethane obtained from azide hydroxyl-terminated polymer cured with isophorone diisocyanate (IPDI)

Chemical structure investigations of polyurethane binders based on difunctional linear glycidyl azide polymer (GAP) cured with isophorone diisocyanate (IPDI) were performed using ¹³C-NMR spectroscopy in solution. Chemical functions such as urethane, urea, allophanate, and biuret were all expected to be detected in these polymeric binders. ¹³C-NMR assignment of the C O urethane and urea functions were found in these polymers as determined by using model compounds of IPDI. The ¹³C-NMR data gathered in this article can be considered as basic parameters for further characterization of polyurethane structure based on IPDI. Also, ¹³C CP MAS NMR spectra of GAP-IPDI-based polymers were carried out to identify the various chemical functions present in solid polyurethane elastomer. In addition, the curing evolution of a GAP-IPDI-based polymer at 50 and 80°C in bulk was monitored, and the reaction path of the binder was readily determined. Some conclusions on the effects of the cure catalyst and the curing temperature were also drawn. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2991–2998, 1997     

Carbon-13 nuclear magnetic resonance of some derivatives of 3-methyl-4,1-benzoxazepine-2,5-dione

Summary ¹³C chemical shift assignment of seven N-derivatives of 3-methyl-4,1-benzoxazepine-2,5-dione is reported. The assignment has been done with the help of J-modulated spectra and by comparison with the values of resembling segments reported in the reference. It has been found that the substituent on nitrogen atom has no significant effect on the¹³C chemical shift of the skeleton.

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¹³C-NMR einiger Derivative des 3-Methyl-4,1-benzoxazepin-2,5-dions

Zusammenfassung Es werden die¹³C-NMR-Verschiebungszuordnungen von sieben N-Derivaten von 3-Methyl-4,1-benzoxazepin-2,5-dionen diskutiert. Die Zuordnungen erfolgten über J-modulierte Spektren und Vergleich von entsprechenden Literaturdaten ähnlicher Molekülsegmente. Es zeigte sich, daß die Substitution am Stickstoff keinen signifikanten Einfluß auf die¹³C-chemischen Verschiebungen der Skelettkohlenstoffatome hat.

     

Application of quantum chemical calculations of C NMR chemical shifts to quinoxaline structure determination

Comparison of experimental and theoretical (GIAO DFT) ¹³C NMR chemical shifts allows the reliable assignment of isomeric structures of heteroaromatic compounds. This methodology was applied to establish the structures of isomeric quinoxalines. A modern 1D NOE technique permitted independent proof of the proposed structures.     

Synthesis and Characterization of Water Soluble Carboxymethyl Chitosan Grafted with Glycidyl Methacrylate

Carboxymethyl chitosan grafted with glycidyl methacrylate was synthesized by the reaction of carboxymethyl chitosan (CSCM) which was prepared from chitosan first and glycidyl methacrylate. The product has been characterized by Fourier transform infrared spectrum (FT-IR), X-ray diffraction (XRD), proton nuclear magnetic resonance (¹H-NMR), solid ¹³carbon nuclear magnetic resonance (Solid ¹³C-NMR), ¹³carbon nuclear magnetic resonance (¹³C-NMR), and chemical analysis, which had different thermal properties from chitosan.     

Automatic assignment of 13C NMR spectra based on the chemical shift/charge density relationship

An approach for the automatic assignment of ¹³C spectra, based on the chemical shift/charge density relationship, is suggested. All permutations of spectral signals are computer-generated, and for every permutation a least squares adjustment is carried out. The permutation presenting the highest correlation coefficient, or the lowest Hamilton's agreement factor, is considered to be correct. The application is exemplified by the ¹³C chemical shifts of a series of aromatic compounds. It is shown that more reliable assignment is achieved if the considered permutations are restricted by taking intoaccount the signal multiplicity.     

13C-NMR.-Substituenteninkremente der N3-Gruppe in Azido-1,4-benzochinonen

¹³C-NMR. Substituent Increments of the Azido-group in 1,4-Benzoquinones The empirical substituent increments of the azido-group in 1,4-benzoquinones have been derived from the ¹³C-NMR. chemical shifts of 2-azido-5-chloro-1,4-benzoquinone. The validity of the obtained values was tested by comparison of the empirical and computed ¹³C-NMR. chemical shifts of other azido-chloro-1,4-benzoquinones.     

A 13C-NMR. Study of cis-trans isomeric vitamins A, carotenoids and related compounds.

The ¹H-decoupled ¹³C-NMR. spectra of 35 all-trans, 17 mono-cis vitamin A compounds (acetates, alcohols, aldehydes, acids and esters) and of one 11, 13-di-cis compound (11, 13-di-cis retinol) are reported. Included in this investigation are desmethyl-, desmethylethyl, and aryl-vitamin A analogues and others as well as 30 reference compounds of smaller molecular weight. Furthermore, the ¹³C-NMR. spectra of 23 β-apo- and other carotenoids were studied. A complete assignment of the signals of all 106 compounds to the specific carbon atoms was achieved by extensive application of lanthanide shift reagents, mainly Yb(dpm)₃, by CW-offset and selective ¹H-decoupling experiments, by comparison of the shifts of related compounds, and in three cases by utilization of specifically deuteriated compounds (11, 12-D₂-retinol and retinyl acetate, 15, 15′-D₂-β-carotene). The chemical shift differences between the cis- and trans-vitamin A compounds and the applicability of the shift reagents for the assignment of the ¹³C-NMR. spectra are discussed.     

Über Polygermane. XIX [1]. Empirische Regelin Zur Abschätzung von 13C-NMR chemischen Verschiebungen in phenylieryten Polygermanen

On Polygermanes. XIX. Empirical rules for estimating ¹³C-NMR Chemical shifts in Phenylated polygermanes ¹³C-NMR chemical shifts are given for 85 phenyl groups independently bonded to Ge in 52 acyclic and 23 cyclic Ge compounds. ¹³C-NMR phenyl signals can be estimated from basic values for perorgano substituted homonuclear chains of Ge nd from increments for substitution at the Ge atoms.