Heteronuclear Overhauser SpectroscopY

For compounds that contain a limited number of fluorine atoms, het-eronuclear 19F-4H 2D NMR experiments such as 19F-4H HETCOR and 4H-19F heteronuclear Overhauser spectroscopy (HOESY) can provide considerable assistance distinguishing structural isomers and diastere-omers as well as for conformational analysis. HOESY experiments have been frequently used for conformational analysis of biomolecules containing fluorine labels.33... 

The 2D sequence [80,81], referred to as HOESY (heteronuclear Overhauser spectroscopy. Fig. 8.52b), avoids the need for selective proton presaturation but naturally suffers from low sensitivity. The sequence parallels that of NOESY,... 

Quantum-chemical analysis of the polyhydrated DNA bases species is still very scarce. The available data are following. The dihydrated complexes of 7GUA and 9GUA molecules were investigated at the MP2/6-31G(d) level [119]. The trihydrated complex of uracil and the corresponding anion radical have been calculated using the 6-31+G(d) level at the HF approximation [127]. In addition, the trihydrated uracil complexes have been the subject of experimental investigations (ID and 2G heteronuclear Overhauser spectroscopy) [128]. 

Heteronuclear Overhauser spectroscopy. 2D H- Li correlation between the Li cation and the copolymer evidencing the preferential soivatation by ethylene oxide segments. From P. Judeinstein, D. Reichert, E. R. deAzevedo, T. J. Bonagamba, Acta Chim. Slav., 2005, 52, 349-60." ... 

The HOESY (Heteronuclear Overhauser Effect Spectroscopy) experiment... 

With the aid of 13C NMR, 6Li NMR and XH HOESY (heteronuclear Overhauser effect spectroscopy) NMR of a-lithiomethoxyallene (106) and l-lithio-l-ethoxy-3-J-butylallene (107) as well as by ab initio model calculations on monomeric and dimeric a-lithiohy-droxyallene, Schleyer and coworkers64 proved that 106 and 107 are dimeric in THF (106 forms a tetramer in diethyl ether) with a nonclassical 1,3-bridged structure. The 13C NMR spectrum of allenyllithium in THF is also in agreement with the allenic-type structure the chemical shift of C2 (196.4 ppm) resembles that of neutral allene (212.6 ppm), rather than C2 of propyne (82.4 ppm). 

Coordination of [6Li]-a-(phenylthio)benzyllithium with 9 was studied by H Li-HOESY NMR technique (HOESY = heteronuclear Overhauser effect spectroscopy) <1998JOM(550)359>. This interaction results in the formation of contact ion pair and ligand and tetrahydrofuran (THF) solvent molecules compete for three coordination sites. The fourth site is occupied by the anionic benzylic carbon atom in an qMike manner. 

A(-Phenylpyrrole (194) is monolithiated at the 2-position of the heterocyclic ring. This monolithium compound crystallizes as the TMEDA-solvated dimer (195). This structure agrees well with the Li- H 2D heteronuclear Overhauser NMR spectroscopy (2D-HOESY). The structure serves to predict correctly that the second lithiation to a dianion occurs at the ortho position of the phenyl ring loca closest to the lithium in the monoanion. 

The tlirough-space nuclear overhauser effect (NOE) can provide information on sites where metals interact even if the metals do not form stable bonds through which spin coupling can be transferred. For instance, metal-HS interactions can be studied by NOE spectroscopy (NOESY) by measuring interactions between the protons within the HS molecules before and after the addition of metals to understand the conformational changes that occur within the molecules (Kingery et al., 2001). An alternative approach is to measure the heteronuclear overhauser effect (HOE) directly between the metal ion and the HS proton in close proximity by HOE spectroscopy (HOES), as has been demonstrated for organo-Li complexes (Bauer, 1995). 

Bauer, W. (1995). NMR of organolithium compounds general aspects and application of two-dimensional heteronuclear Overhauser effect spectroscopy (HOESY). In Lithium Chemistry, ed. Sapse. A.-M., and Schleyer, P. V. R., Wiley-lnterscience, New York, 125-172. 

A different approach to locate the metal in a lithium organyl, which exploits dipolar rather than scalar interactions, was presented by the group of Berger who appUed both 2D- C, Li HOESY and lD- C Li difference spectroscopy to measure C, Li heteronuclear Overhauser effects and demonstrated that the resulting data can be used for C-Li distance calculation. Ihe major drawback of this technique is that the use of doubly [ Li, C]-labelled samples is mandatory to ensure reliable measurement of very small NOE effects of some 1%. 

W. Bauer, NMR of Organolithium Compounds General Aspects and Application of Two-Dimensional Heteronuclear Overhauser Effect Spectroscopy. In Lithium Chemistry (Eds. A.-M. Sapse and P.V.R. Schleyer), Wiley, New York, 1995, pp. 125-172. 

Chiappe et al. reported the use of rotating-frame Overhauser spectroscopy (ROESY) and HOESY to investigate two pyrazolium-based ILs with different anions [83]. Using homo- and heteronuclear NOE, they showed the presence of aggregation, how sensitive the aggregation is to steric hindrance, and the nature of anions. Specifically they found that aggregation motives are in a head-to-tail and head-to-head manner. From the HOESY experiments, the researchers probed the formation of loose ion pairs, which are also sensitive to steric effects. Castner s group has utilized H— F HOESY to probe-specific cation—anion interactions for isoelectronic... 

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