NMR study of ring opening reaction of epoxidized natural rubber in presence of potassium hydroxide/isopropanol solution

The ring opening reaction of epoxidized natural rubber (ENR-50) in the presence of potassium hydroxide/isopropanol solution was studied using NMR, and it's thermal characteristic was investigated using TG/DTG and DSC. ¹H-NMR showed that 16.9% of epoxide units was ring-opened in treated ENR-50, which was also supported by quantitative FTIR spectroscopy. ¹³C-NMR proved the location of alkyl group (isopropyl) in the polymer chain of treated ENR-50. The attachment location of isopropyl occurred at both most (↑) and least (↓) hindered carbons of the epoxide. 2D-NMR was used to identify and scrutinize the triad assignment of treated ENR-50. The TG/DTG results presented three decomposition steps at 190-331, 331-521 and 521–706 °C due to the existence of mixtures of polymer chains i.e. ring-opened and intact epoxide of ENR-50, which also led to increase in T_g of treated ENR-50 at 13.2 °C compared with purified ENR-50 at −17.7 °C.     

Quantitative Analysis of Clove Oil by NMR Spectrometry

A procedure utilizing NMR spectrometry in the quantitative analysis of clove oil is described. The ¹H-NMR spectrum is determined with acetophenone as internal standard, the ¹³C-NMR spectrum is determined with chloroform as internal standard and 0.1M Cr(acac)₃ as relaxation reagent. The contents of eugenol are compared to the results obtained from G.C. (90.8%, s.d. 0.7%) and from chemical method (89.6% s.d. 1.2%). The result obtained from ¹H-NMR method is 90.4% (s.d. 0.3%) and from ¹³C-NMR method is 90.5% (s.d. 0.7%). The time required for the ¹H-NMR method is about 20mins and for the ¹³C-NMR method is about 2-3hours. Apparently the ¹H-NMR method proves to be more simple, rapid and accurate.     

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.     

Radical cyclocopolymerization of divinyl ether and maleic anhydride. A 13C-NMR study of the polymer structure

The structure of the 1:2 copolymer of divinyl ether and maleic anhydride was investigated by ¹³C-NMR spectroscopy. The polymer contains the bicyclic unit composed of one molecule of each monomer and the maleic anhydride unit. The carbon chemical shift for these units was calculated on the basis of the chemical shift of many model compounds. The major peaks of the cyclopolymer prepared in chloroform were consistent with the presence of the symmetrical bicyclic unit with cis junction and the trans monocyclic anhydride unit. The carbonyl carbon spectrum for the copolymer obtained in a mixed solvent of acetone and CS₂ suggested the predominant formation of the unsymmetrical bicyclic unit. The polymerization process was discussed on the basis of these results.     

乙基纤维素三甲硅基衍生物膜的结构表征与氧氮渗透行为

Characterization of ethyl cellulose and its derivative membranes EC-SiMe3 was studied by ¹H-NMR, ¹³C-NMR, solids-state ¹³C-NMR(CPMAS) and IR spectra. The permselectivity for oxygen and nitrogen of EC-SiMe3 membranes was determined.     

Synthesis,Spectroscopic Studies and Keto-Enol Tautomerism of Novel 1,3,4-Thiadiazole Derivative Containing 3-Mercaptobutan-2-one and Quinazolin-4-one Moieties

In this study, a novel 1,3,4-thiadiazole derivative containing 3-mercaptobutan-2-one and quinazolin-4-one moieties (Compound 3) is synthesized by the coupling of 2-amino-1,3,4-thiadiazole-5-(3-mercaptobutan-2-one) (Compound 1) with 2-Phenyl-4H-3,1-benzoxazin-4-one (Compound 2) in one molecule moiety. Compound 3 is found to exist as two types of intra-molecular hydrogen bonding with keto-enol tautomerism characters, which is further confirmed using FTIR, ¹H-NMR, ¹³C-NMR, mass spectrometer, and UV-Visible spectra. The ¹H-NMR and UV-Visible spectra of Compound 3 are investigated in different solvents such as methanol, chloroform, and DMSO. Compound 3 exhibits keto-enol tautomeric forms in solvents with different percentage ratios depending on the solvent polarity. The ¹H-NMR and UV-Visible spectral results show that Compound 3 favors the keto over the enol form in polar aprotic solvents such as DMSO and the enol over the keto form in non-polar solvents such as chloroform. The ¹³C-NMR spectrum gives two singles at δ 204.5 ppm, due to ketonic carbon, and δ 155.5 ppm, due to enolic carbon, confirming the keto-enol tautomerism of Compound 3. Furthermore, the molecular ion at m/z 43 and m/z 407 in the mass spectrum of Compound 3 and fragmentation mechanisms proposed reveal the existence of the keto and enol forms, respectively.     

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     

Characterization of aromatic polymers (benzenoid and heterocyclic) by cross-polarization,magic-angle 13C-NMR spectroscopy

The cross-polarization, magic-angle ¹³C-NMR spectra of solid samples of poly(p-phenylene), its nitro derivative, polymerized biphenyl, poly(p-phenylene sulfide), poly(1-methyl-2,5-pyrrolylene), poly(1-phenyl-2,5-pyrrolylene), poly(2,5-thienylene), and poly(2,5-selenienylene) and the high-resolution ¹³C-NMR spectrum of poly(m-phenylene) in solution are presented and assigned. In all cases the chemical shifts are similar to those of model compounds in solution. In most instances the resonances of the nonprotonated carbon atoms in the solid polymers are more intense than those of the protonated carbons and appear to depend on the charge distribution in the molecular orbitals.     

The use of carbon black-supported sulfuric acid to initiate the cationic polymerization of cyclic ketene acetals

Stable polymers were made by the cationically initiated 1,2-polymerization of cyclic ketene acetals employing heterogeneous, activated carbon-supported sulfuric acid catalysts. A methodology has been established for the preparation of the carbon black of different acidic strengths. By adjusting either the acid strength or the amount of carbon black used, cyclic ketene acetals with different activities can be polymerized efficiently to form stable high molecular weight polymers. This methodology will be a useful tool for polymerization, copolymerization, and studies of the relative reactivities of the cyclic ketene acetals. The polymer structures were determined by FTIR, ¹³C-NMR, and ¹H-NMR studies. © 1996 John Wiley & Sons, Inc.     

Differential Hydrogen Exchange During Biosynthesis of Cytochalasins B and D

Sodium [2-¹³C,2-²H₃]acetate was incorporated into cytochalasin B( 1 ) by Phoma exigua and into cytochalasin D ( 2 ) by Zygosporium masonii. The ¹³C-NMR. and ²H-NMR. of the metabolites showed that most of the deuterium was lost except at carbon atoms which are in polyketide chain-initiating units.     

Zur Kenntnis des Chinoiden Zustandes—XX: 13CMR-Untersuchungen an Cyclohexadienonen

The ¹³C-NMR-chemical shifts of 19 para- and 5 ortho-cyclohexadienones are determined by ¹³C-Fourier-transformation spectroscopy and assigned. The effect of substituents on the chemical shift of the ring carbon atoms is discussed. The mutual dependence of the shifts of the olefinic ring carbons and the allylic carbon atom in the para-quinolid ring system is shown by computing regression lines. A frequently observed correlation between ¹³C-NMR and ¹H-NMR is examined in the case of cyclohexadienones.     

Investigation of the intramolecular structure of styrene–ethylmethacrylate copolymers by 1H- and 13C-NMR: Reassignment of 1H-NMR spectra

The compositions and sequence distributions of homogeneous styrene (S)–ethyl methacrylate (E) copolymers, obtained by low conversion solution polymerization have been studied by ¹H- and ¹³C-NMR. A new set of peak triad assignments was proposed for the δ 2.1–4.2 ppm region in the ¹H-NMR spectrum, whereby the reactivity ratios of r_S = 0.59 and r_E = 0.50 were used to establish this new assignment. The EEE and SSS blocks, present in these copolymers, have a high degree of syndiotacticity (σ_EE = 0.23, σ_SS = 0.39), whereas the ESE units are exhibiting a slight tendency toward isotacticity (σ_ES = 0.66).     

Acid catalysed rearrangements of iridoid aglycones—II : Tetracyclic acetal from asperulosidol,a non natural asperuloside derivative

The acid catalysed rearrangement of asperulosidol 5 leads to the tetracyclic acetal 7 whose structure and configuration has been determined by ¹H-NMR and ¹³C-NMR spectroscopy, as well as by the Li/NH₃ reduction of 7 to the cyclopententriol 10. The reaction course has been clarified by reacting 5 with DCl and formation of the monodeutero derivative 9.     

Bulky organosilicon compounds based on sulfanyltetrazoles: their synthesis and in vitro antibacterial evaluation

The study introduces different organosilicon derivatives incorporating sulfanyltetrazole ring for biological applications. Initially, the sulfanyltetrazole derivatives and halo-analogues (Br, I) were synthesized. Later, selective reaction of tris(trimethylsilyl)methyllithium (TsiLi) in the presence (?46 and 0 °C) and absence (room temperature) of CS₂ with halo-sulfanyltetrazole derivatives yielded new multifunctional sulfanyltetrazole regioisomers with SH, C = S, ethynylthio and SiMe₃ groups, respectively. All the synthesized compounds were characterized by IR, ¹H-NMR, ¹³C-NMR spectra and elemental analysis data. The compounds were screened for their antibacterial activities against clinically important gram-positive and gram-negative bacteria using the spectrophotometric microdilution method. The preliminary screening indicated that the organosilicon derivatives incorporating SH and C = S (mercapto-silyl-thiones) and silyl-thioalkynes have antibacterial activities, whereas no antibacterial activity was observed on compounds containing (Me₃Si)₃C groups. Of the synthesized compounds, compound 5d showed the best activity against all the tested organisms (3.91–31.25 µg/mL).     

A NEW PEAK (T_4) IN THE ~(13)C-NMR SPECTRUM OF POLYBUTADIENE

A new peak at 39.0 ppm in the ~(13)C-NMR spectrum of polybutadiene (PBD) was discovered. This peak is assigned to the fourth peak (T_4) of trans-1,4-sequence marked with an asterisk as shown in Fig. 3 in the text.The occurrence of T_4 carbon nuclei is strongly affected by their neighboring 1,2-units. So long as both contents of trans-1,4- and 1,2-units attain their proper amounts the peak (T_4) with appear in the ~(13)C-NMR spectrum of PBD.     

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.     

Stable polymers from cyclic ketene acetals: Cationic polymerization initiated by acid-washed glassware or acid-washed glass beads

Stable polymers were made by the cationic 1,2-polymerization of cyclic ketene acetals initiated by acid-washed glassware or acid-washed glass beads. Among several reactions possible for the very reactive cyclic ketene acetals, only the corresponding acetals of polyketene were formed. These structures were demonstrated by FTIR, ¹H-NMR, and ¹³C-NMR analyses. © 1996 John Wiley & Sons, Inc.     

~(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。     

Fungal extractives—VI : Structure of lactaral,a new sesquiterpene furan-3-aldehyde from Lactarius,by spectroscopic methods

The structure of a new sesquiterpene furan-3-aldehyde from Lactarius vellereus and L. pergamenus has been elucidated by means of IR, UV ¹H- and ¹³C-NMR spectroscopy and computer simulation of the ¹H-NMR spectrum.     

Über Chalkogenolate. 159. Umsetzung von 1,2-Ethandithiolaten mit Kohlenstoffdisulfid 1. Darstellung und Eigenschaften von 1,2-Ethan-bis(trithiocarbonaten)

On Chalcogenolates. 159. Reaction of 1,2-Ethanedithiolates with Carbon Disulfide. 1. Synthesis and Characterization of 1,2-Ethane-bis(trithiocarbonates) The reaction of 1,2-ethanedithiolates with carbon disulfide forms the corresponding 1,2-ethane-bis(trithiocarbonates). The compounds M₂[S₂C? SCH₂CH₂S? CS₂] with M = Li, Na, K, Rb, Cs, NH₄, Tl have been characterized with chemical methods as well as by means of electron absorption, infrared, nuclear magnetic resonance (¹H and ¹³C), and mass spectra.