Variable temperature, H NMR spectra

FIG. 36. Variable-temperature H NMR spectra of [TpBul]BeH. Reprinted with permission from Ref. (56). Copyright 1992 American Chemical Society. 

Figure 1.21 Variable temperature H NMR spectra in CD2CI2, showing the passage from a slow to fast exchange for the two halves of the bipyridine ring in 92.

Figure 2.3 Variable-temperature H NMR spectra recorded in a hexamethyl phosphoric triamide solution of 2,6-dihydroxybenzoic acid at 135, 163, 177, and 240 K. (Reproduced with permission from ref. 26.)...

Figure 3.10 Variable-temperature H NMR spectra of complex 107 in acetone-dg solution.

Figure 3.21 Variable-temperature H NMR spectra of 124 in acetone-de solution. The resonances assigned to the new derivative are indicated. The inset corresponds to the spectrum at -80"C for a solution with an AgBF4 Phdat ratio of 2. 

Variable temperature H-NMR spectra of 5-nitroso-2,4,6-trimethyl-5,6-dihydro-4H-1,3,5-dithiazine (464) (all three methyl groups shown to be cis by X-ray crystallography) gave an unusually low barrier to rotation about the N—N bond (17.2 kcal mol-1) attributed to the electron-withdrawing sulfur substituents and steric crowding.359... 

Variable-temperature H NMR spectra were measured for 177 and 178 in CD2CI2 solutions205. In the former the N-methyl groups and the methylene protons appeared as sharp singlets down to the lowest attainable temperature, while in 178, with two chiral centers, signals due to only one diastereomer could be observed, and the initially diastereotopic N-methyls (due to the chiral carbon center) coalesced with an activation... 

Figure 8.63 Variable temperature H NMR spectra of the Ir—H and N—H regions in 8.50 showing the proton exchange process. (Reproduced with permission from The Royal Society of Chemistry).

The compound (LXIV) (entry 14) provided an early example of a stereochemically nonrigid bridged system. Variable-temperature H-NMR spectra showed it to be fluxional at room temperature. A number of related systems have now been studied, including (OC)3Co(M-GeMe2)2Co(CO)3 (5), (CpXCO)Fe(M-COXp.- GeMe2)Fe(CO) (Cp) (4), and (OC)3Fe(/i-CO)(/i-SnR2)2Fe(CO)3 (213). All are fluxional, although the second becomes so only above about 90°C. 

An analysis of variable-temperature H-NMR spectra showed that Fe(II)-OEC possesses rhombic magnetic anisotropy (85JA4207). 

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.

The variable temperature H NMR spectra of 17 and 18 indicate exchange events similar to those observed by Marks and coworkers for standard metallocenes.15 In this equilibrium process (Scheme 4), the enantiomeric species represented by I interconvert via a solvent separated ion-pair dissociation/recombination process. It is typically assumed that the highest energy species corresponds to structure II. 

Fig. 1-16. Variable temperature H NMR spectra of l- (dppf-P, P )Pd BjH7 (adapted from [61]).

Fig. 1-23. Variable temperature H NMR spectra of Re2(/t-OMe)2(CO)6(/t-dppf) (adapted from [74]).

X = NH2 or NHPh (80d,e) the equatorial position was preferred. The possible reasons for this are discussed and variable-temperature ( H, NMR spectra reveal some unusual intramolecular processes within these compounds. ... 

Fig. 2. Low range variable temperature H NMR spectra of 2c in CD2CI2 solution.

Figure 2.8.5 Molecular structure of 14 and its variable temperature H NMR spectra...

Group 11. Paramagnetic (1H, 15N) NMR spectra were used to study a Cu -IDA (=iminodiacetic acid) complex localised on a protein surface. H and 13C NMR spectra were reported for copper(II) bis-benzimidazole complexes.1225 Variable temperature H NMR spectra of copper complexes of p-octafluorinated triarylcorroles reveal a thermally-accessible paramagnetic excited state, i.e. a Cu11 corrole 7i-cation radical.1226 Copper(II) forms of stellacyanin from Rhus vernicifera were characterised by H NMR.1227... 

To our complete surprise, variable temperature H NMR spectra of representative N-acyl piperazic acids showed no evidence of conformational motion from -89 to +120°C. This implied that the molecules in question possess an unusual degree of conformational... 

It was not possible to derive the thermodynamic parameters for the skeletal rearrangements of (2) and (3) from variable-temperature H NMR spectra. 

Calculated at 298.15 K by band-shape analysis of the methylene hydrogen signals in variable-temperature H NMR spectra. 

Fig. 2. Pore size distribution of a silica with nominal pore diameter of 200 A. The solid line gives that determined from variable-temperature H NMR spectra of adsorbed cyclohexane, while the points give that determined by conventional gas adsorp-tion/desorption measurements. (Reproduced with permission from ref. 41, 1993, American Physical Society.)...

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