Analysis, NMR

The radical-catalyzed polymerization of furan and maleic anhydride has been reported to yield a 1 1 furan-maleic anhydride copolymer (89,91). The stmcture of the equimolar product, as shown by nmr analyses, is that of an unsaturated alternating copolymer (18) arising through homopolymerization of the intermediate excited donor—acceptor complex (91,92). 

Conjugate Addition. To a solution of 1.5 mmol of lithium dialkylcuprate at — 25 CC is added 1 mmol of methyl ( )-3-[(25,45,55)-3-benzyloxycarbonyl-4-methyl-5-phenyl-2-oxazolidinyl]-propenoate dissolved in 1 mL of dry diethyl ether. After 30 ntin at — 25 C, the mixture is treated with an aq NH3/NH4C1 pH 8 buffer solution and then stirred at r.t. for 15 min. After diethyl ether extraction, the organic layers are dried over Na,S()4 and filtered and the solvent is evaporated under reduced pressure. The crude products are checked by H- and l3C-NMR analyses in order to determine the diastereomer ratios (g 95 5) and then purified by flash chromatography (hexane/ethyl acetate 80 20) yield 70-72%. 

Ciguatoxin. The toxin was isolated from moray eels and purified to crystals by Scheuer s group (1). Structural determination of the toxin by x-ray or NMR analyses was unsuccessful due to the unsuitability of the crystals and due to the extremely small amount of the sample. The toxin was presumed to have a molecular formula of C Hg NO from HRFAB-MS data (MH+, 1111.5570) and to have six hydroxyls, five methyls, and five double bonds in the molecule (2). The number of unsaturations (18 including the five double bonds) and the abundance of oxygen atoms in the molecule point to a polyether nature of the toxin. The toxin, or a closely related toxin if not identical, is believed to be the principal toxin in ciguatera. Ciguatoxin was separable on an alumina column into two interconvertible entities presumably differing only in polarity (J). 

Peaks are analyzed separately by their retention times, absorption, and fluorescence properties. RCCs show absorbance maxima near A.500 and 316 nm. For FCCs, UV-Vis specna show two prominent bands near 361 and 320 mn and a luminescence maximum at 436 mn and NCCs show UV-Vis spectra with absorbance maxima near 320 and 210 nm. Nevertheless, as none of these approaches is suitable for elucidating structures, it is necessary to apply additional MS and NMR analyses to fully characterize snuctural features. Electron spray ionization (ESI) and high-resolution EAB mass spectroscopy have been applied to elucidate the molecular formulae of colorless compounds. ... 

Both MS and NMR coupling to HPLC have been employed for the analysis of p-carotene isomers and determination of lutein and zeaxanthin isomers in spinach, sweet com, and in retina. Capillary high performance hquid chromatography with stop flow connected to NMR (600 MHz) was used for stracture elucidation of all-trans deoxylutein 11 and its isomers.Efforts are in progress to eliminate the remaining major drawbacks such as obligatory use of deuterated solvents in the mobile phase, poor sensitivity, and low throughput of HPLC-NMR analyses. 

The product was isolated and identified by H NMR and NMR analyses comparing with the authentic 2,6-dihydroxybenzoic acid as a reference. 

In the reaction of lactic acid to form pyruvic acid over the iron phosphate catalysts, formation of a new compound was observed. As the extent of reaction increased, the amount of pyruvic acid increased to a maximum and then decreased, while that of the new compound increased steadily. It was therefore concluded that the new compound is formed from pyruvic acid in parallel with acetic acid and CO2. According to gas-mass analyses, the molecular weight was determined as 112. However, there are many compounds with molecular weigth of 112. After the NMR analyses and X-ray diffraction analyses for the single crystal, the new compound was determined to be citraconic anhydride, i.e., mono-methyl maleic anhydride. 

Preparative-scale fermentation of papaveraldine, the known benzyliso-quinoline alkaloid, with Mucor ramannianus 1839 (sih) has resulted in a stereoselective reduction of the ketone group and the isolation of S-papaverinol and S-papaverinol M-oxide [56]. The structure elucidations of both metabolites were reported to be based primarily on ID and 2D NMR analyses and chemical transformations [56]. The absolute configuration of S-papaverinol has been determined using Horeau s method of asymmetric esterification [56]. The structures of the compounds are shown in Fig. 7. 

However, is supercomplex 27 the true intermediate As previously mentioned, Sugasawa reported that reaction did not proceed with N,N-dialkyl anilines. Do N,N-dialkylanilines form a similar supercomplex We examined the following three anilines, ArNH2, ArNHMe, and ArNMe2, as shown in Figure 1.3. Under Sugasawa conditions at room temperature, formation of the corresponding supercomplex, respectively (29,30, and 31) was confirmed, based on their NMR analyses (Complex 29 and 31 were derived from toluidine and complex 30 comes from aniline). 

The nmr analyses of the bottoms products given in Table IV show the material to have a large aliphatic content. The aromatic/aliphatic ratios of the fractions are higher than for the whole coal because of the presence of combined phenol reaction with Tetralin reduces these ratios considerably, presumably by transfer of much of this material to the solvent-range product, but some of it must remain in the bottoms as the aromatic/aliphatic ratio of the composite bottoms product from the fractions is higher than that from the whole coal. It was not possible to calculate the contribution that the diluents, excess solvent and combined phenol, made to the aromatic H, but the large monoaromatic content of the bottoms product must be due, in part, to these. 

Transalkylation might be expected another kind of the solvolitic reaction. However, the present results suggest low probability with alkylated pyrenes as suggested by the NMR analyses. Instead, the increased polarity by alkyl group or the enhanced reactivity of the carbonization precursor from alkylpyrene, especially ethylpyrene, may be responsible for a considerable liquefaction yield. The recovery of the solvent becomes difficult by its latter conversion as observed in the present study. 

Several aluminum biphenolate complexes have been investigated as initiators for the ROP of PO.810,935 Unlike the TPP and salen-based systems, a cis coordination site is realistically accessible and in theory an alternative cis-migratory mechanism to the backside attack pathway might operate. However, NMR analyses on the resultant PPO show that stereochemical inversion still occurs when the biphenolate initiators are used (Scheme 22). It has also been confirmed that the same process occurs with the Union Carbide calcium alkoxide-amide initiator for both PO and CHO.810... 

It is well know that the zeolite materials synthesized in alkaline systems usually have a high number of silanol groups (=SiOH) named defect groups [10] which possess a moderated Bronsted acidity [11]. Oppositely, Silicalite-1 synthesized in fluorine media are relatively defect-free [12] and the fluorine ions remain in the small cages of the MFI structure even after the calcination process [12]. The 29Si-NMR analyses carried out on samples Na-Silicalite-1 and F-Silicalite-1 confirm the presence of silanol groups only on the SI support surface (results not showed). Delaminated zeolites (ITQ-6) are obtained by exfoliation of as-synthesized lamellar precursor zeolites [13]. After this process, the final structure of the delaminated zeolite results in a completely hydroxylated and well-ordered external surface [13]. 

An examination of the products formed by bromination of furan disclosed only addition. These were very unstable and could not be isolated but NMR analyses showed that both 2,5-dibromo-2,5-dihydrofuran (cis and trans) and 2,3-dibromo-2,3-dihydrofuran (trans only) were formed. Eventually only 2-bromofuran is left, but whether the additions are side equilibria or genuine stages on the way to the substitution product is not yet known.148... 

The major current limitation of NMR is its sensitivity (ca. 10-4 M in ll, 13C, 19F, 31P). It is expected that higher sensitivities will be reached in the future as more powerful magnets with improved instrumentation and software become available. The ultimate goal would be to perform NMR analyses of single molecules. 

Useful information on the nature of the active sites can also be obtained by 13C NMR analyses of the polymers produced. These analyses indicate that some active sites can interconvert in a time shorter than the average time of chain growth118 120 and that at least one of the active sites has an environment of Ci symmetry.119... 

NMR-analyses suggest that the hydrogenation runs corresponding to Scheme 10.3. Three of the four possible catalyst-substrate complexes are detectable in the 31P-NMR-spectrum [57 f]. 

Because most common solvents, including water, contain protons, and most NMR analyses involve the measurement of protons, a solvent without protons is generally used in NMR spectroscopy. Commonly, solvents in which the hydrogen atoms are replaced with deuterium (i.e., solvents that have been deuterated) are used, the most common being deuterochloroform. In addition, an internal standard, most commonly tetramethylsilane (TMS), is added to the sample in the NMR sample tube (see Figure 14.3, D) and all absorption features are recorded relative to the absorption due to TMS. 

In view of the inherent resistance of some surfactant metabolite isomers to complete mineralisation, efforts have to be mounted in order to obtain further insight into the reasons behind the persistence of these, such as the SPC and nonylphenol ethoxy carboxylates (NPECs). In order to achieve this, it would thus be indispensable to be able to fully elucidate the chemical structure of individual components, e.g. after isolation from environmental samples. Through the application of, for example, LC-ESI-MS-MS in combination with NMR analyses, this is now possible. 

Careful 1H and 13C NMR analyses were carried out for both monomers and polymers in order to prove the chemical structures of the polymers. The H NMR spectra of 50 and 52 are shown in Figure 8. As polymerization proceeded, an acetylenic proton peak at 2.0-2.2 ppm disappeared, while a new vinylic proton peak appeared broadly in the 6.8-7.2 ppm range. Since the new peak is weaker than those for the aromatic biphenyl rings and the two peaks are superimposed, it is hard to separate them clearly. The broad peaks at 2.6 and 3.4 ppm are assignable to the methylene protons and methine proton in the ring, respectively. 

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