Complete line shape analysis

The l3C-NMR spectrum of the ethyl-substituted derivative at — 80°C is consistent with the cis-cis-trans conformation and a complete line-shape analysis of the coalescence of the CH2N resonances at higher temperatures gives AG 11.76 0.2 kcal mol-1 at — 40°C for the inversion processes 357 358 359.302... 

Complete line shape analysis over this temperature range. 6In CDC13. 

From complete line shape analysis (02CEJ3016). Calculated by molecular mechanics. 

Finally, the ring interconversion of dodecamethylcyclohexasilane 180 was studied at very low temperatures by complete line shape analysis (98JOC9125) the free energy of activation is 4.7 kcal/mol and the interconversion was suggested to be the same as that of cyclohexane-like derivatives. The higher flexibility of 180 was also found in the solid state. 

Nitrites exist as a mixture of the syn and anti forms, in dynamic equilibrium. The rate of configurational isomerisation in methyl nitrite has been determined by NMR complete line-shape analysis , and the following parameters were derived Ea = 11.1 kcal.mole S A = 2x10 sec (at 237° K) and AS = —3.5 eu (237 °K). The isomerization mechanism is believed to be intramolecular, involving partial delocalization of the N=0 double bond. 

From this, and in some cases from a complete line-shape analysis, free energies or enthalpies of activation have been derived for the processes equilibrating the fluorine atoms between axial and equatorial sites. Data for a representative range of ligands are summarized in Table 5. 

The kinetics of these processes were measured at 25 °C by complete line-shape analysis of the H NMR spectra. The racemization reaction of [(D-pcn)(Z.-pen) TcO] proceeds nearly 60 times faster than the racemization of the corresponding complex of rhenium [61]. 

The complete line shape analysis of the variable-temperature H NMR spectra of the Cr(CO)s[W(CO)s]- -1,3,5-trithiane complexes provided precise energy barriers for the 1,3-intramolecular shift of the Cr(CO)s and W(CO)5 moieties 83 (Scheme 11) <1983POL1117>. The corresponding 2,4,6-trimethyl-l,3,5-trithiane derivatives yielded the free energy of activation for the 1,3-shifts which proved to be largely dependent upon the skeletal flexibility of the 1,3,5-trithiane ligand. The kinetic parameters of the 1,3-shift in 83 are given in Table 7. 

Figure 2.11 Determination of the activation parameters of the [1,3]-B shift in 22 by complete line-shape analysis.

DOSY has been used to demonstrate catenation in (31). and Si NMR spectroscopy has been used to show [naphthylSi(OH)3] encapsulated in (32). The NMR signals of complexes of a s-[PtCl2(NH3)2] with DNA have been assigned. J( Pt N) has been determined accurately for [Pt(NH3)Cl3] by complete line shape analysis. Pt NMR spectroscopy has been used to study aromatic ring stacking between Pt complexes with aromatic amino acids and mononucleotides.It has been shown that cis- and trans-complexes of [Pt(NC5H5)2(N03)2] can be differentiated by H, and Pt NMR spectroscopy. A method for the calculation of J( Pt H) and Ti( Pt) in... 

Before the advent of multipulse techniques the determination of the components of a, J, q, and D in solids could be carried out only for favorable systems (with very large shielding anisotropies or quadrupole coupling constants) by complete line shape analysis or second moment analysis of the wide line NMR spectrum obtained. Now NMR spectrometers are commercially available for high-resolution spectroscopy in solids. Depending on the nature of the system and of the information desired, some combination of the previously mentioned techniques is used. We give only a few examples here because the field is still taking fast strides. 

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