75As-NMR

Static 75As NMR of the CT in powdered films of Al Ga As has been used to obtain information about possible ordering in this alloy. The milligram quantities used were obtained by an epitaxial lift-off process from the MOVPE growth substrate and subsequent pulverization. Signals from 75As[A14] and 75As[Ga4]... 

The existence of oxaarsetanes during an arsa-Wittig reaction has been proved by H and 170 NMR spectroscopy.40 75As NMR spectra were obtained from the corresponding arsonium salts and arsane oxides. It has been shown that the reaction mechanism of the arsa-Wittig reaction is identical with that of the phospha-Wittig reaction. 

The configurations at phosphorus in compounds 73-76 were assigned on the basis of II-NMR data assuming that in phosphorus-containing heterocycles, the protons in a 1,3-m-relation to a P=0 group are deshielded. Thus, since H4 and H5 resonate at lower field in compounds 73a-76a than in compounds 73b-76b, the P=0 group must be cis to H4 and H5 in the a series [32]. These assignments were fully supported by the crystal structure studies of 75a, which showed that this... 

SB. Actually, these tautomeric equilibria are more complex because each of these three forms can exist as two geometric isomers ( and Z for 75A and 75A) or two conformers (rotamers E and Z for 75B). When + H, two diastereomers cis and trans and R ) are possible for the cyclic tautomer 75B. These equilibria have been thoroughly investigated (88TH2) by means of electronic, IR, H-, and C-NMR spectroscopy. The structure of the solid 5-hydroxypyrazoline 74B- (R = Me R = H R = Ph R" = i-Pr) was confirmed by X-ray diffraction (87MI5). An approximate generalization of the influence of the structural factor on these equilibria is shown in Table X. 

The dimeric complex 74 reacts with phenylacetylene or ferrocenylacetylene to yield the tetrameric complexes 75a and 75b, respectively, according to equation 26. These complexes are stable in CDCI3 solution in the absence of air and can be characterized by H and NMR spectroscopies. The low solubility of 75a in unreactive organic solvents precludes detailed studies of the solution structure in reactive solvents it decomposes to a dimeric complex, 76, according to equation 27 3. j jjg association behavior of these complexes resembles that of analogous organolithium compounds - 303... 

Reactions of 5f/-2-methyl-l,2,4-triazepino[2,3- ]benzimidazol-4-one 71, prepared by reaction of 1,2-diaminobenz-imidazole 72 with acetoacetic ester 73, with different reagents was described, in the search of new heterocycles with biological activity <2002CHE598>. When lactam 71 was treated with aromatic aldehydes in boiling 1-BuOH with addition of piperidine 74, 577-3-arylidene-2-methyl-l,2,4-triazepino[2,3- ]benzimidazol-4-ones 75a-c were obtained (Scheme 7). Coupling lactam 71 with phenyldiazonium chloride 76 in dioxane afforded the 3-phenylazo-substituted tricycle 77. When 71 was treated with phosphorus pentasulfide 78 in boiling dioxane or pyridine, its thio analog 79 was obtained. The reaction proceeded most efficiently when lactam 71 was refluxed with twofold excess of 78 in dry dioxane. These thiones 79 react with ammonia and amines by nucleophilic substitution. When 79 was refluxed with ammonia, benzylamine, piperidine, or morpholine, the 4-amino-substituted tricycles 80a-d were obtained. All the described compounds were identified by NMR, mass spectrometry, and IR spectroscopy. 

In contrast, approach to the structure determination by solid-state NMR [86], has proposed a more defined geometry of both the macrocycle and the side chain. In fact, the 10 solid-state NMR structures derived were very well defined, while the average RMSD of the heavy atom to the X-ray structure was only 0.75A. When comparing assignments of the solid-state NMR with the previously reported solution-state NMR data [84], a qualitative correlation was found between the chemical-shift variations observed and the possibility of intermolecular hydrogen-bonding [86],... 

Blinc et al.10 have reviewed the present understanding of two recent advances in proton and deuteron glasses namely, (a) the determination of (Jea and W(p) in the "weak substitutional disorder" limit (J0>J) via 75As NQR and NMR and (b) the application of 2D "exchange" deuteron NMR to the study of deuteron inter- and intra-bond transfer rates in deuteron glasses on time scales 1-103 s. 

Preparation of the first-generation dendrimer appeared to yield chiral 75a,b without any problems. The CD spectra for both enantiomers showed the expected Cotton effects, but the mass spectra did not exhibit correct molecular peaks. As we found out by NMR spectoscropy, a mixture of stereochemically pure, once- and twice-substituted products was formed. The mass spectra showed peaks at half the mass of the molecular ion, but they do not arise from the tetranitriles 75a,b as predicted, but resulted from decomposition of the chiral amines 74a,b probably due to steric crowding. 

In contrast, introduction of a trigonal atom at the 9-position should decrease the flagpole-flagpole repulsion and thus increase the content of a CB conformer in the equilibrium. The study of the conformational equilibrium of bicyclo[3.3.1]nonan-9-one (75) at room temperature using shift reagents and H-NMR techniques made it possible to determine the content (22%) of conformations CB + BC (75a, 75c) (58). 

The only example of this type of base is crotanecine (126), and its structure and stereochemistry were deduced by comparison of its NMR and mass spectra with those of the most widespread pyrrolizidine base, retronecine (127).84 The magnitude of the vicinal coupling constants of the protons on C-5 of crotanecine (126), 75 6 = 9.5 Hz and 75a 6 = 6.5 Hz, are consistent with the 6/ -hydroxy group and an exo-buckled ring. The other vicinal coupling constants, J6x l = J18 = 3.5 Hz are indicative of a 7/ -hydroxy group, as in retronecine (127). 

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