Variable-temperature , 1H NMR

To obtain further information on the structure of 14, a variable-temperature 1H-NMR measurement was carried out. Coalescence of the para-methyl signals at 2.06 and 1.96 ppm at 44 °C, reflecting a conformational change of the molecule, was observed with an activation free energy of A= 17.0 kcalmol-1. The two pairs of four resonances of mefa-protons between 6.7 and 6.3 ppm and mesityl orf/zo-methyl protons between 3.3 and 2.3 ppm also coalesce at 60 °C and 80 °C, respectively (Figure 7). Afor the coalescence of both the meto-protons and orf/zo-methyl groups at the coalescence... 

Figure 1. Variable-temperature 1H NMR spectra of compound 12 top, 403 K middle, 353 K bottom, 298 K.

Fig. 7.20. Variable temperature 1H NMR data (formylic proton) for [Tm(DMF)g](C104)3 in DMF (a) reduced chemical shift, and (b) transverse relaxation rate. The measurements were performed at 60 MHz (O) and...

Reversible fac-mer isomerization of the [LaCl3(HMPA)3] complex studied by variable temperature 1H NMR spectroscopy gave evidence for an associative mechanism [82], However it is not possible to distinguish between associative interchange mechanism and seven coordinate intermediate. An equilibrium mixture of [LaCl3(HMPA)3] and [LaCl3(HMPA)4] is also a possibility. 

Successive deprotonation of [P NH(Ph) ]+ was followed by 31P NMR spectroscopy.1110 Formation constants for adducts of C60 and C70 with a number of phosphine oxides were calculated from 3H chemical shift changes in the systems.1111 Variable temperature 1H NMR spectra of [L]BiN03, where L =... 

The activation energy AG for silicon-nitrogen cleavage (eq. [103]) was determined from variable temperature 1H NMR studies of derivatives of 231 (133). 

The following dynamic process has been established for 27 by variable-temperature 1H- and 31P-NMR studies... 

Proton and I3C NMR spectra have been used to distinguish between symmetrically (N-2) and asymmetrically (N-l) coordinated benzotriazole (209) or 4,5-disubstituted triazolate (109, 146) ligands, and to measure equilibrium constants for the N-l/N-2-coordinated benzotriazole system [Fe(CN)5(btaH)]3 (209). Hydrogen bond formation and proton transfer reactions in [Fe(taH)(C5H5)(CO)2][HSOJ have been followed by variable-temperature 1H and 13C NMR (5,146). 

The variable-temperature 111 NMR spectrum for RuL(napy-K27V,7V)(dmso)]n+, where L = V-mcthyl-3,5-di(2-pyridyl)-4-(pyridyl) n = 2 L = 2,6-di(2-pyridyl)phe-nyl, n = 1, napy = 1,8-naphthyridine, show fluxionality of the chelated napy in solution 920 Proton NMR data gave information about intramolecular rearrangements in RuCyPPh2(2,6-Me2C6H3]2.921 Variable-temperature 111 NMR data for [Ru(OAc)(CO)2(dpa)]2, where dpa = di(2-pyridyl)amine, show fluxionality at room temperature 922 Similar data (plus 31P 1H spectra) for Ru(RCOO)2(dppf) (R = Me, Et, Ph dppf = l,l -bis(diphenylphosphino)ferrocene) show uni- and bidentate exchange behaviour of the carboxylate ligands 923... 

The proton NMR spectrum of CpRh(pesa)Cl, where pesa = (I )-V-[(S )-l-phenylethyl]salicylaldimine, gave data on the rate of epimerisation of this complex.936 Variable-temperature 31P 1H NMR spectra of [3,3-(PPh3)2-8-L-c/oio-3,l,2-RhC2B9Hio], where L = SEtPh, were used to follow fluxional behaviour.937 Variable-temperature 3H NMR spectra of [Rh(L)(CO)]PF6 (where L = 2,6-bis(benzylthiomethyl)pyridine) showed fluxional behaviour typical of S,N,S-donor ligands, due to pyramidal inversion at S centres.938 The fluxional behaviour of [Rh(C0)L(PPh3)2]C104, where L = bis(ben-zimidazol-2-ylmethyl)methylamine, was studied similarly.939... 

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... 

In the case of allylpotassium, the metal complex exists as a symmetric n structure. No temperature dependence was shown by either 13C NMR for A5[C(i) —C(3)] or by 1H NMR for substitution with deuterium at Cp). Thompson and Ford measured experimentally a variety of allylalkali metal compounds using variable-temperature NMR in THF-dx45. Addends such as TMEDA, hexamethylphosphoric triamide (HMPA), 15-crown-5-ether, [2.1.1]cryptand and n-butyllithium showed either no change in the spectrum or rapid decomposition of the complexing agent. Measurement of the populations of E (17) and Z (18) isomers of 1-isopropylallylpotassium showed the Z isomer to be more stable (Table 11). 

Exarchou, V. et al., Do strong intramolecular hydrogen bonds persist in aqueous solution Variable temperature gradient IH, 1H-13C GE-HSQC and GE-HMBC NMR studies of flavonols and flavones in organic and aqueous mixtures. Tetrahedron, 58, 7423, 2002. 

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