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H and 10 13C NMR Spectroscopy

Most of the reported 1,2,5,6-tetrazocine systems probably do not exist in the monocyclic form but rather as the tetraazapentalene betaine structure (see Introduction) 2 3 7"13 for the tetra-phenyl-substituted system, the compound does actually exist as the mesoionic tetraphenyl-[1,2.3]triazolo[l,2-h][l,2,3]triazole, as determined by H and 13C NMR spectroscopy.15 The following syntheses arc therefore questionable. [Pg.558]

The free ligands were obtained by visible photolysis in acetonitrile and were characterized by elemental analyses and H- and 13C-NMR spectroscopies. Low-temperature reduction in ESR tubes also provided the green Fe1 19e complexes which gave the characteristic 3g values typical of the rhombic distortion of Fe1 [77],... [Pg.70]

The relative configurations and predominant conformations of [l,2,3]oxathiazino[4,3- ]isoquinoline derivatives 177-182 were studied by means of H and 13C NMR spectroscopy with the applications of DNOE, 2D HSC, and 2D-COSY measurements. Their stereostructure includes an equilibrium between the conformers cis-1, trans and cis-2. In the /ra -structure, the B/C rings are trans-ane-WatcA with H-l lb and the N-5 lone electron pair trans-diaxial. In the cis structures, the hetero-rings are air-anellated in the cis-1 conformation C-l is in inside position, while in cis-2... [Pg.245]

Reaction of dimethyl acetylenedicarboxylate (DMAD) with extremely unstable mesomeric betaine 96, generated in situ from 95, gives in 30-36% yield of a 1 2 adduct, the structure of which was originally determined as 97 <1978CL1093>. However, a more recent reinvestigation based on the H and 13C NMR spectroscopy shows that the actual product is pyrazolo[l,5- ]azepine 98, formed probably by mechanism shown in Scheme 6 <1995JCM338>. [Pg.383]

Ab initio calculations predicted that if 99 and 47 could be generated in the absence of a nucleophile then the sole product would be the azoniatricylene 3. This was proved to be the case by reacting 98a or 98b with AgBF4 at low temperature. The product was confirmed to be 3 in each case by H and 13C NMR spectroscopy. [Pg.1053]

In the Baeyer-Villiger oxidation of [4.3.3]propellane-8,ll-dione 74 the propellane-bis-lactones formed, 75 and 76, are accompanied by a dispirolactone 77 22. Different product mixtures result when different (acidic or more basic) reaction conditions are employed but it has been shown experimentally for the head-to-tail propellane bis-lactone 75, vis-a-vis the isomeric dispiran 77, the latter appears to be the thermodynamically more stable product, resulting from the former under acidic conditions (p-TsOH/ C6H6, 7 days, r.t.). The structures were established by means of X-ray diffraction and H- and 13C-NMR spectroscopy. [Pg.16]

The measurement of pA bh+ and m values is sometimes complicated by the fact that the spectroscopic methods used (generally H and 13C NMR spectroscopy, and UV-vis) are subject to medium effects. Water and (say) 80 wt% H2SO4 are very different media, and it is not very surprising that spectral peaks for the same species in the two media can occur at different wavelengths or different chemical shifts. Several methods have been devised for handling this problem 24,99,100 the excess acidity method lends itself to dealing with medium effects quite well.101... [Pg.22]

By using H and 13C NMR spectroscopy, Watson et al. <2004JOC6105> could assign the structure of each pyrrolam regioisomer 10-12. [Pg.5]

To date the structure and reactivity of numerous complexes derived from aromatic compounds and nitrosonium cation have been studied (5, 56-63). However, relatively few studies are available on the nitrosonium complexes of cyclophanes (5, 57, 59, 61, 62), cf ref. (63). The interaction of [2.2]paracyclophane with nitrosonium tetrachloroaluminate was studied by H and 13C NMR spectroscopy using deuterium isotope perturbation technique (64). It was found that the resulting nitrosonium complexes containing one (25) or two NO groups (26) are involved in fast interconversion (on the NMR time scale) (Scheme 17). [Pg.142]

Upon reaction of O-mesitylsulfonylhydroxylamine with X-1,10-phenanthrolines (56a-d) in CH2C12 the respective isomeric cations (55a-d) and (57a,e-g) were formed (Scheme 24) (99), and their structures were confirmed by H and 13C NMR spectroscopy. [Pg.150]

Stereoselective aldol condensations provide a-substituted /J-hydroxycarbonyl compounds328, and it transpires that H- and 13C-NMR spectroscopy are excellent tools for determining their relative configurations. For example, it has been pointed out329 330 that the vicinal 1H,1H coupling constant is a good indicator of the stereochemistry (see Table 2)331 ... [Pg.329]

Cody, G., Alexander, C.M. O. D. and Tera, F. (2002) Solid state ( H and 13C) NMR spectroscopy of the insoluble organic residue in the Murchison meteorite a self-consistent quantitative analysis. Geochimica et Cosmochimica Acta, 66, 1851-1865. [Pg.380]

The FOZ of A1 -alkenes singly substituted on position 3 with an alkyl group or with various open-chain and ring ketones (299) can be structurally characterized by H and 13C NMR spectroscopy. Thus, with one exception the proton denoted as H shows a singlet at 8 = 4.98 to 5.04 ppm whereas H and H" show a singlet and a triplet, respectively,... [Pg.724]

The structure of the stable ozonide of a diterpene (300) was elucidated based on knowledge of the original structure assisted by H and 13C NMR spectroscopies. Thus, a 13C NMR DEPT experiment points to the presence of six quaternary C, six CH, three... [Pg.725]

In 3-substituted thiophenes these absorptions are found in the ranges 1555-1481, 1443-1392, 1374-1355 and 1235-1193 cm-1 and the hydrogen in-plane absorption is found in the range 1098-1070 cm-1 (63JCS3881), It is not too likely that one would use IR data as a definitive structural tool in view of the more revealing structural information available from H and 13C NMR spectroscopy. [Pg.738]

In a crystal structure47111-ds-retinal has the 12-s-cis conformation shown at the top in Eq. 23-36 rather than the 12-s-frans conformation at the center and in which there is severe steric hindrance between the 10-H and 13-CH3. Nevertheless, H-and 13C-NMR spectroscopy suggest that the retinal in rhodopsin is in a twisted 12-s-frans conformation.472 4723 The Schiff base of 11-ds-retinal with N-butylamine has an absorption maximum at -360 nm but N-protonation, as in the structure in Eq. 23-36, shifts the maximum to 440 nm with emax = 40,600 M 1 cm 1 (Fig. 23-42). This large shift in the wavelength of the absorption maximum (the opsin shift) indicates that binding to opsin stabiliz-... [Pg.1326]

A number of adducts of bis(acetylacetonato)nickel(lI) have been studied by H and 13C NMR spectroscopy.39739,407"423 In several cases, always when aromatic bases are involved, the shifts of both protons and carbons cannot be accounted for by cr- and r-delocalization mechanisms. Similar results have been found for non-aromatic amines such as piperidine derivatives, showing that in these complexes there are also alternating 13C contact shifts which have been accounted for by inclusion of spin polarization in the mechanism of electron spin transfer through the carbon skeleton with INDO-MO calculations.412... [Pg.57]

FIGURE 25.5 Distribution of furanose, pyranose, and open-chain forms of D-ribose in aqueous solution as measured by H and 13C NMR spectroscopy. [Pg.1046]

Benzotriazole reacts with the complex anion [Fe(CN)5(H20)]3 to afford a mixture of N-2- and N-3-coordinated isomers [Fe(CN)5(btaH)]3 characterization by H and 13C NMR spectroscopy yielded an equilibrium constant K = 1.9 + 0.3 favoring the less symmetric N-3 isomer (209). Relaxation times obtained from cyclic voltammetry data indicate an intramolecular mechanism for the (N-2) (N-3) isomeri-... [Pg.182]

H- and 13C-NMR spectroscopy of a solution of 13 in KNH2/NH3 shows that H-l and C-l have undergone upheld shifts of 4.24 ppm and 83.7 ppm, respectively (Tables II and III).20 This is due to the formation of 1-amino-dihydro-2,6-naphthyridinide (14). Because 2,6-naphthyridine is reported to have the lowest electron density at position 11819 (Table I), the formation of cr-adduct 14 is in good agreement with these calculations. The spectrum of... [Pg.105]

However, 3-methyl-1,8-naphthyridine (37b) reacts with KNH2/NH3 in a completely different way than do 37a and 37c.15 H- and 13C-NMR spectroscopy unequivocally show the formation of the 1 1 cr-adduct 2-amino-3-methyldihydro-l,8-naphthyridinide (40) (Table V). No addition at C-7 is observed, although this position is also vulnerable to nucleophilic attack (see Section II,A,4). Similar behavior has been found in the Chichibabin animation of 3-methylpyridine the amide predominantly attacks C-2 and not C-6.33 This result has been explained by an ion dipole attraction between the incoming amide ion and the methyl substituent.34 This type of attractive interaction also possibly determines the attack on C-2 in 37b. [Pg.114]


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