High-temperature H-NMR

In both cases, only one diastereomer could be detected using high-temperature H NMR spectroscopy. Removal of the oxazolidinone auxiliary from compounds (S,S)-101 and (/ ,R)-101 by treatment with lithium hydroperoxide followed by acidification and treatment with diazomethane generated the corresponding methyl esters (S)-102 and (/ )-102 which have opposite configuration at C2. Amination of either... 

Figure 3-19 High-temperature H NMR spectrum of Acemannan , acetate fingerprint, 300 MHz, solvent DjO at 353K, "SSL".

Dfaz, M.C., Edecki, L., Steel, K.M., Patrick, J.W., and Snape, C.E. Determination of the effects caused hy different polymers on coal fluidity during carhonization using high-temperature H NMR and rheometry. ji rg Fu 2008 22 471 79. 

Miyazawa, K., Yokono, T., Sanada, Y., Yamada, E., and Shimokawa, S. High-temperature H-NMR study of coal and pitch at the early stages of carbonization. Carbon 1979 17 223-225. 

P NMR data have been reported for Ir4(CO)8(PPh2Me)4 [6 -8.4(1), —40.6(2), 61.6(1) p.p.m.] together with a variable temperature H NMR study, which indicates that phosphine intra-exchange occurs at high temperatures whereas the low temperature spectra are consistent with a number of alternative stereochemical arrangements46. ... 

The low temperature H-NMR spectrum (CD2C12, — 40°C) of 2,5-dimethyltetrahydro-1,2-oxazine (equilibrium shown in Fig. 10) shows an equilibrium between 229 (95%) and 232 (5%).239 The N-Meax conformers 230 and 231 are neglected because even tetrahydro-1,2-oxazine itself exists exclusively as the /V-Heq conformer,237 and calculations on hydroxylamine indicate a very high energy for conformations that correspond to axial N-substituents.240 Thus the conformational free energy of the 5-methyl group may be estimated as 1.36 0.1 kcal mol -1 at —40°C.239... 

Fig. 44. High-resolution H NMR spectra with MAS and WHH-4 sequence of 88% NH -exchanged zeolite NH4-Na-Y at various activation conditions quoted as temperature (400, 450, and 500°C) and deep bed (DB) or shallow bed (SB) (170).

Synthesis of Glycoluril la A modification of the literature procedure was used [33], To a solution of urea (600 g, 10 mol) in water (1 L) was added a 40% aq. solution of glyoxal (500 g, 3.45 mol) and cone. HC1 (86 mL). The resulting solution was heated at 85-90 °C until a heavy precipitate was formed. The reaction mixture was allowed to cool to room temperature and filtered. The filter cake was washed with copious amounts of water (2 L) followed by acetone to remove residual water. The resulting white solid (397.5 g, 81%) was dried under high vacuum. H NMR (DMSO, 400 MHz) 7.11 (s, 4H), 5.20 (s, 2H). 

Chlorohydridobis(tricyclohexylphosphine)nickel is a yellow-brown solid. It is thermally stable at ambient temperature but reacts with air. It is very soluble in benzene, tetrahydrofuran, and dichloromethane and is soluble in diethyl ether and petroleum ether. Carbon tetrachloride, carbon disulfide, and chloroform decompose the complex. The infrared spectrum shows a sharp v(Ni—H) band at 1916 cm-1 (KBr disk and Nujol mull). The high-field H nmr spectrum in benzene solution has a triplet (1 2 1) at t34.6 (TMS) with JpH 73.5 Hz. The splitting is caused by the coupling of the hydride proton with two equivalent 31P nuclei. This is consistent with a trans square-planar configuration. 

Fig. 5. Variable temperature H NMR spectra of 4h (high-held region) in CD2C12 solution showing exchange of V-methyl groups without exchange of diastereomers.14 Reproduced with permission from the American Chemical Society.

A variable temperature H NMR study of the above compound has been undertaken. Despite the presence of a surfeit of exchange processes, it was concluded that this [2]-catenane is a highly ordered molecular assembly in solution. ... 

Fig. 4. High range variable temperature H NMR spectra of 2c in C6D5NO2 solution.

Variable-temperature H-NMR studies on 7-acetyl-3-methylanthranil (161 X = O) indicate that there is a high interconversion energy barrier between the two identical valence tautomers.215 In contrast, there is no evidence for a similar interconversion with the 7-acetylbenzisothiazole (161 X = S),215 nor for the methyl 3-methoxyanthranil-7-carboxylate (147 X = Y = O).169... 

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