13C-NMR spectral studies

Another example is dimethyl 3,6-dichloro-l-tosyl-l//-azepine-4,5-dicarboxylate which, on the basis of ]H and 13C NMR spectral studies, is a 9 1 equilibrium mixture of azepine and benzene imine tautomers at —70 C(AG = 50.16 kJ mol-1) 22 however. X-ray analysis indicates that the mixture crystallizes as the 1//-azepine isomer. 

C NMR spectral studies whereas 172 with ethylamine gave 174, the dihydro derivative 173 formed 175.145,146... 

Takahashi, S.-L, Fujimoto, T., Bama, B.M., Miyamoto, T., Inogaki, H., 1986, 13C-NMR spectral studies on the distribution of substituents in some cellulose derivative. J. Polym. Sci.. Part A Polym. Chem. 24 2981-2993. 

Hufford et al [13] used a 13C NMR spectroscopic method for the assignments of dissociation constants of primaquine. The first and second dissociation constants of primaquine were determined by titration with 0.1 N hydrochloric acid in acetonitrile-water mixtures and values were extrapolated to water by using linear regression analysis. The assignments of the dissociation constants were unambiguously achieved by studying the 13C NMR spectral data obtained with monohydrochloride, dihydrochloride, and trihydrochloride salts. 

Proton and 13C NMR spectral data of 33 derivatives of 64 have been tabulated and assigned <1996MRC409>. Several 3-oxo derivatives of 64 have been studied by proton and 13C NMR spectroscopy as part of a comprehensive investigation of their structural and spectroscopic properties <2003BCJ2361>. The regioselectivity of the formation of the six-membered ring in derivatives of 67 from 1,3-diketones has been established by proton NMR spectroscopy and nuclear Overhauser effects <1997CHE535>. 

Their studies revealed that acylation occurs preferentially at N(l) leading to a 40% yield of l-(ethoxycarbonyl)-7-methyl-l/7-pyrrolotetrazole 38 along with traces (4.6% yield) of l,5-bis(ethoxycarbonyl)-7-methyl-l//-pyrrolotetra-zole 39. The 1/7-pyrrolotetrazole structures of 38 and 39 were established by comparison of their 13C NMR spectra with a model 1//-isomeric system 40. Additional support for the l//-isomeric system came from 13C NMR spectral comparisons with pyrrolotetrazoles 41 and 42 that are representatives of the 2H- and 3//-systems. These studies showed that the 13C NMR spectral data presented earlier by Dulcere and co-workers <1990JOC571> in a previous acylation study of the monoanion 37 was not compatible with what was believed to be the 5//-pyrrolotetrazole 43. 

The ring-inversion process in Af,N-dimethylhexahyd ropyrimidine has been estimated by H-NMR spectral studies as AG. 3r 11.6kcal mol-1 297 and AGi29 4" 11-3 kcal mol"1 298 Variable-temperature 13C-NMR work287 permits the estimation of AG values (Table XXVII) for the N-inversion process in the /V,/V-dimethyl- and JV,JV-diethylhexahydropyrimidines. 

The pyrones and thiinones show general 13C NMR spectral characteristics similar to the pyridones which reflect charge distributions in the heterocyclic rings. Thus, carbon atoms a or y to the heteroatom are deshielded relative to benzene, while those (3 are shielded. Substituent effects are in general as expected, although fewer detailed studies have been carried out in this area with the oxygen and sulfur heterocycles than with the azines. Chemical shift data for representative compounds are given in Scheme 10. 

C NMR spectral investigations have been extended566 to the study of heteroaromatic stabilized 6n 3-dioxolium and 10ji benzo-3-dioxolium ions 273 and 274. 

Ln3+ induced water 170 shifts of [Ln(DOTA)] solutions show that the hydration number of the complexes is one across the lanthanide series [59]. The substantial pseudocontact contribution to its LIS indicated that this water ligand has a preferred location in the complex. Two sets of peaks have been observed in H and 13C NMR spectra of [Ln(DOTA)] complexes at room temperature showing the presence of two slowly interconverting structural isomers [60-63]. In the spectra of the paramagnetic complexes, one isomer has larger LIS values than the other. These structural features have been confirmed by luminescence studies [51, 64]. The temperature dependence of the H and 13C NMR spectral features of both the dia- and paramagnetic Ln3+ complexes indicates that the... 

Also, recent developments in quantum theoretical calculations of NMR parameters have increased their reliability and usefulness, especially in studying the dynamic processes such as conformational equilibria and tautomerism of aniline derivatives. All the above-mentioned items will be included in the following discussion. However, owing to the huge amount of data about H NMR parameters, the main focus of this review is directed to 13C, 15N and 19F NMR spectral studies of aniline derivatives. Schiff bases are not included in this review although some of them show an amino-imino tautomerism and can thus be considered as anilines. One reason for this is that a search in Chemical Abstracts using key words schiff base and nmr produced more than 1000 hits. 

As an example of suspected endocrine disruptors (EDs), studies of the estrogenic action of bisphenol A (BPA) have been in progress in medical, physiological, and biological fields. In this situation, physicochemical approaches are required to get the structural information of BPA trapped in biomembranes. Most recently, we have determined the site and the orientation of BPA trapped in phospholipid vesicles by NMR, using the HCS rule [47], In particular, we have succeeded in monitoring the 13C NMR spectral changes of phospholipid vesicles, which are induced by the BPA delivery. 

Recently, the structure of alkaloid A has been revised (102) from 83 to 85, mainly on the basis of 13C NMR spectral correlation of alkaloids A and with those of closely related neoline-type alkaloids. The reinvestigation of the structure of alkaloid A by the, 3C NMR analysis was carried out because the position of acetoxyl group at C-8 in alkaloid A was rendered doubtful by the data from the pyrolysis study. The 13CNMR analysis reveals that an a-acetyl group is present at the C-6 position instead of at C-8 and that a methoxyl group is present at the C-8 position. We have also revised the 13C chemical shift assignments of alkaloid A (85). 

NMR spectral studies suggest that the alkene tether of 12c is positioned on the secondary rim of J -CD. The photocyclization of 12c affords the minor product 13c in the highest ee of 17%, but the major product 14c in only 2% ee. As illustrated in Fig. 1, this phenomenon can be rationalized as a result of the tradeoff between chemical and optical yield, as larger steric hindrance leads to low yield and high ee, while smaller steric hindrance results in high yield and low ee. 

Very recently there has been an experimental and theoretical study of electronic substituent effects in 4-aminoaryl (4-substituted aryl) sulfones146. PMR, 13C NMR and infrared measurements were involved and semi-empirical all-valence CNDO/2 calculations, with and without sulfur d orbitals, were carried out. Various correlations between spectral results and substituent constants are presented. There is good agreement between experimental and theoretical data, which does not depend on the inclusion or exclusion of the sulfur d orbitals from the calculations. 

Hufford et al [57] used proton and 13C NMR spectrometric data to establish the novel sulfur-containing microbial metabolite of primaquine. Microbial metabolic studies of primaquine using Streptomyces roseochromogenus produced an A-acety-lated metabolite and a methylene-linked dimeric product, both of which have been previously reported, and a novel sulfur-containing microbial metabolite. The structure of the metabolite as an S-linked dimer was proposed on the basis of spectral and chemical data. The molecular formula C34H44N604S was established from field-desorption mass spectroscopy and analytical data. The 1H- and 13C NMR spectra data established that the novel metabolite was a symmetrical substituted dimer of primaquine A-acetate with a sulfur atom linking the two units at carbon 5. The metabolite is a mixture of stereoisomers, which can equilibrate in solution. This observation was confirmed by microbial synthesis of the metabolite from optically active primaquine. 

A subsequent study of A. cavernosa from Thailand by California workers revealed two additional F-type kalihinols in addition to kalihinol-X (109) and -Y (110) [45]. The structures of kalihinol-I (121) and -J (122) were secured by low resolution chemical ionization mass spectral and NMR data. Both 1H-1H COSY and 13C NMR techniques were used extensively. Furthermore, hydrolysis of compound 109 to kalihinol-J (122) confirmed the assignments. 

Analogous to the DuP 747 study, complete crystallographic information was not possible on the fosinopril sodium polymorphic system [25], Two known polymorphs (A and B) were studied via a multidisciplinary approach (XRD, IR, NMR, and thermal analysis). Complementary spectral data from IR and solid state 13C NMR revealed that the environment of the acetal sidechain of fosinopril sodium differed in the two forms. In addition, possible cis-trans isomerization about the CgN peptide bond may exist. These conformational differences are postulated as the origin of the observed polymorphism in fosinopril sodium in the absence of the crystallographic data for form B (single crystals not available). 

Besides the electronic spectral studies noted above, we have also carried out in situ studies of the acidic ruthenium catalyst using nmr and infrared spectral techniques. A key set of observations derive from the and 13C nmr spectra of an operating catalyst at 90° and Pco 1 atm which indicate the presence of only one major ruthenium species. The proton spectrum shows a sharp singlet at 24.0 T which remains such when the solution is cooled to room temperature, although the slow formation of other species was observed over a period of hours at the latter conditions. The 1H-decoupled 13C spectrum of the... 

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