NMR Spectroscopy in Solution

One of the most powerful and widely used methods in the study of carbocations is NMR spectroscopy. This method yields information about the cation 

Early observations of stable carbocations in solution relied heavily upon H NMR spectroscopy. Subsequently, C NMR spectroscopy has proved to be an even more useful technique. C NMR permits also the direct observation of the cationic center and the observed chemical shifts and coupling constants can be correlated to the cation geometry and hybridization. 

With high sensitivity, high resolution superconducting NMR spectrometers, rate constants of degenerate rearrangement of the order of 10 s or less may be determined. This corresponds to a process with a free energy of activation threshold of 3.3kcalmol at -160 C.  

Very slow exchange can be detected and the rate measured by the transfer of spin saturation technique, a tool that can be useful in the elucidation of reaction mechanisms causing exchange. One of the signals participating in very slow exchange is saturated by an external radiofrequency (RF) field while the rest of the spectrum is observed. If exchange of the spin-saturated nuclei takes 

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In contrast to TeFe, mixtures of SeFg and H20 appear not to interact over long time intervals at room temperature (57). HOSeFs and possibly HSe03F, however, are detected by, 9F-NMR spectroscopy in solutions of selenic acid in AHF (57). 

Isomers of pentaborane and hexaborane derivatives SnPh2(BsHg)2 and Ph3SnB6H9 were studied by H, nB, 13C, and 119Sn NMR spectroscopy in solution and solid state structures of three isomers were also reported.50-53... 

Miura, T., Klaus, W., Gsell, B., Miyamoto, C., and Senn, H. Characterization of the binding interface between ubiquitin and class 1 human ubiquitin-conjugating enzyme 2b by multidimensional heteronudear NMR spectroscopy in solution./. Mol. Biol. 1999, 290, 213-28. 

Sesbanimide is a novel cytotoxic compound isolated from Sesbania puni-cea seeds [84JCS(P1)1311]. According to high-field H- and C-NMR spectroscopy, in solution a solvent-dependent equilibrium exists between the... 

One hydroperoxide 152 was isolated and the stereochemistry proven by NMR spectroscopy in solution and by X-ray crystallography in the solid state <2005JOC251> (which therefore represents one of the very rare examples of peroxide crystal structures). 

P R E CONTENTS Preface. Stable-Isotope Assisted Protein NMR Spectroscopy in Solution, Brian J. Stockman and John L. Mar-kley. 31P and 1H Two-Dimensional NMR and NOESY-Dis-tance Restrained Molecular Dynamics Methodologies for Defining Sequence-Specific Variations in Duplex Oligonucleotides, David G. Gorenstein, Robert P. Meadows, James T. Metz, Edward Nikonowcz and Carol Beth Post. NMR Study of B- and Z-DNA Hairpins of d[(CG) 3T4(CG)3] in Solution, Sa-toshi Ikuta and Yu-Sen Wang. Molecular Dynamics Simulations of Carbohydrate Molecules, J.W. Brady. Diversity in the Structure of Hemes, Russell Timkovich and Laureano L. Bon-doc. Index. Volume 2,1991, 180 pp. 112.50/E72.50 ISBN 1-55938-396-8... 

IR and Raman spectra of ofloxacin and levofloxacin were measured and evaluated [06SA(A)159]. Saccharin salt of ofloxacin was prepared and characterized by FTIR, X-ray powder diffraction, thermal analysis, and and 13C NMR spectroscopy in solution and in solid state (09JPS3788). Nondestructive discrimination between levofloxacin and ofloxacin containing tablets was achieved by using diffusion reflectance NIR spectroscopy (08PHA628). 

In Table 1 we have summarised the observed binding sites for Pt(II) to DNA fragments, usually proven by X-ray crystallography in the solid state, and by NMR spectroscopy in solution. It is not possible to review here the great variety of studies dealing with structural and spectroscopic studies on coordination compounds with nucleobases and derivatives. 

Our last study concerning indazoles was an experimental (X-ray crystallography, NMR spectroscopy in solution and in the solid state) and theoretical study of fluoro-substituted indazoles 43-46 [51],... 

Surprisingly, some 2,3,6-substituted pipecolic acid derivatives like 2 favor exclusively the anti amide isomer [19]. The anti preference of 2 has been demonstrated by NMR spectroscopy in solution (methanol and DMSO) and X-ray analysis in the solid state. The reason for this unexpected finding is the special arrangement of substituents on the pipecolic heterocycle. In contrast to compounds like 1, the additional bulky substituent attached to C3 forces the carboxy group at C2 into an equatorial position and the substituent at C6 into an axial position. 

One-dimensional 119Sn NMR spectroscopy in solution was used to characterise soluble polymer-supported organotin compounds181,199. To get a more detailed understanding of the microstructure of tin-containing polymers, 1H/13C/119Sn triple resonance 3D NMR... 

From 1,3,5-trisilacyclohexane a number of titanium complexes Cp Ti (/i-0)3[Si(/bu)-C[ I2]3 were analyzed by 111, 13C, and 29Si NMR spectroscopy in solution and by X-ray structural analysis in the solid state (02MI). 

In our calculations He have taken into account the oligomers identified by NMR spectroscopy in solutions of analogous compositions (9.10). He have checked that the concentrations of the other theoretically possible species are indeed completely negligible. 

The related intramolecular monoalkene complexes of R3E + cations, the nor-bornyl cations of group 14 elements (Si —> Pb), have been synthesized with TPFPB as counteranion and characterized by NMR spectroscopy in solution supported by quantum mechanical calculations.40 Only the acetonitrile complex, 73, of the plumbanorbornyl cation 13 could be characterized by X-ray crystallography. Similar to the structure of the plumbyl cation 74, the Pb atom in the acetonitrile complex 73 adopts a trigonal-bipyramidal coordination sphere with the C = C double bond and the acetonitrile in the apical positions and the Pb atom in the center of the trigonal plane (see Fig. 11 and Table XIV, for details).40... 

The structure of 2-substituted 4-(2-furyl)-5-nitrothiazoles [543], 5-nitrothiazolyl-2-semicarbazides (homolog of strong antitrichomonade agent) [539] was proved by II NMR spectroscopy. The NMR spectra were used for the identification of 5-nitrothiazole 2-amino derivatives [532, 544, 545], The polymorphic azodyes containing 2-amino-5-nitrothiazole have been investigated by multinuclear NMR spectroscopy in solution and in solid-state (13C CP/MAS) [544, 545],... 

The microstructures of polyolefin materials are most effectively studied by C NMR spectroscopy in solution. In particular C atoms at branching positions and at the ends of chains and branches are easily distinguished from those inside a chain. In this way, the numbers and mean lengths of branches, e.g. in polyethylene chains, can be determined rather reliably. 

From reaction in solutions, a variety of polyphosphides is obtained that are not known as solvent-free binary compounds (Table 7). Several have been characterized by P NMR spectroscopy in solution, for example, Pi9 and P26" , which have no counterparts in binary systems. LiPs forms a to(P5 ) polyanion in the solid state, but the corresponding anion in solution is monomeric Ps, an analogue of the cyclopentadienyl anion. The helical polyanions do(P7 ) of LiP and NaP have no monomeric counterpart in the solution here the anion is present as R2P7. Adding simply a salt (KI), trimeric P2i is formed as a finite anion in solution and it can be isolated as a solvated salt. 

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