F Chemical Shifts

Fig. 5. Dependence of the spin-spin coupling-constant and the F chemical shift on the oxidation state of the central xenon atom.

Inductive and resonance parameters, (Tr°, ct, were evaluated for the isocyanide ligand from F chemical shifts they suggest that the isocyanide is a good cr-donor and a weak ir-acceptor. 

The meta- and para-isomers of the phosphoranes (FC6H4)3P(OEt)2 have been prepared from the corresponding phosphines and diethyl peroxide. From their F chemical shifts it was concluded that the groups... 

Figure 2 compares the results of theory and experiment for the specific case of p-fluoronitrobenzene. Inspection of the calculated structure shows that the proton is still on the zeolite, and the F shifts are more like chloroform solution than superacid solution. Furthermore, when the l F chemical shift was calculated for the theoretical structure, it was found to agree with the experimental result. 

TABLE 4.4. F Chemical Shifts of Secondary CF2 Groups—Effect of P-Halogen... 

TABLE 4.6. F Chemical Shifts of CH3XCF2H Compounds— Effect of a-Substitution... 

As in the case of the HN(CO)CA-TROSY scheme, the HN(CO)CANH-TROSY experiment can be readily expanded to a four-dimensional HN(CO)CANH-TROSY experiment without increasing the overall length of the pulse sequence. This can be accomplished by labelling the 13C (f) chemical shift during additional incremented time delay, implemented into the 13C — 13C INEPT delay. As a result, a well-dispersed 13C (i- 1), 13C (i- 1), 15N(i), Hn(0 correlation map is obtained with minimal resonance overlap albeit with the inherent sensitivity loss by a factor of y/2. 

Fl.T. Tran, Q. Guo, D.J. Schumacher, R.B. Buxton, R.F. Mattrey, F chemical shift Imaging technique to measure Intracellular p02 in vivo using perflubron, Acad. Radiol. 2 (1995) 756-761. 

Provided that the above interpretation of the F chemical shifts is well-... 

Table 14. F Chemical Shift (C6D6) of the Two CFj-Signals of Diastereomeric Imidazolidines Derived from Selected Aldehydes (Data Adapted from ref 65)...

A comparative study of the variation in the F chemical shift of the P F " resonances of complexes 5 or 27 on addition of increasing amounts of the salt KPFe was carried out. The resonances were compared with those of free RPF. The results are represented in Figure 3.8. A similar study was carried out with the BF4 complexes 6 and 28 and the salt NBU4BF4. For the complexes, the chemical shift of the anion is different to that of the free salts. When an increasing amount of the salt is added the chemical shift changes and it approaches that of the free anion. This observation points to the existence of some cation-anion interaction in solution that modifies the anion resonances. A F, H-HOESY experiment confirmed the existence of these contacts in the case of complex 27. A correlation between the fluorine resonance of the PFg anion and the protons of the pyridazine ring indicates that the counter-anion... 

The HNMR and PNMR were recorded on a Nicolet spectrometer operating at 282 MHz and 35°C. The F chemical shifts of the products are converted to 6-values upfield from fluorotrichloro-methane by using the value of 61.9 ppm for 1,2-dichloro-l,1-di-fluoroethane. The 1atter.compound CH2C1CF C1 was added as an internal standard. The aFNMR data of the products show AB... 

TABLE 4.7. 14 F Chemical Shifts of CH3XCF2H Compounds - Effects of a-Suhstitiition... 

None of the other eight terms represents Up U coherence transfer. We also ignore the s s c" and s c s" multipliers since they carry the F chemical shift and. /-coupling information—we are only interested in the F2 slice. What do these two terms look like in FF> Remember that the Ha resonance (I ) is a doublet of doublets... 

Fig. 9. Evolution with time of the NMR characteristics of AIPO4—02. (a) pH variation at 150°C from, 4N NMR (b) A1 atomic fraction in solution versus time at 150°C (c) in situ 27Al NMR spectra during the first 5 h of synthesis at 150°C (d) in situ l9F at 150"C (e) in situ 27A1 NMR spectra during nucleation and growth (f) chemical shift evolution of the prenucleation cluster peak vs time (with courtesy of C. In Gerardin and F. Taulelle).

From the F chemical shifts in the NMR spectra of m- and/>-fluoro-phenylcopper were calculated the substituent parameters for copper. The zero value obtained for oj suggests that copper is electronically neutral, but a large or value indicates that copper is capable of a d interaction with the aromatic nucleus 37). The high stability of penta-fluorophenylcopper tetramer relative to many other arylcopper compounds may thus be the result of interactions between the five fluorine atoms and the benzene ring increasing the charge density of the 7r-elec-tron system 37). 

---