F-NMR Spectra

For cyclooctane, a total of 11 conformations have been suggested for consideration and their relative energies calculated. The boat-chair was calculated to be the most stable conformation. This prediction was confirmed by analysis of the temperature dependence of the F-NMR spectra of fluorocyclooctanes. The activation energy for interconversion of conformers is 5-8 kcal/mol. A few of the most stable conformations are shown below. 

Consistent with this, the F nmr spectra of solutions at 0° showed the presence of HSO3F, and separate cryoscopic experiments with pure H2SO4 as the sole solute gave a value of u close to unity. 

Ir- and F-NMR spectra were determined for all soluble polymers. Most of the HFB polymers (8a-e) showed good solubility in common solvents (e.g., THF, CHCI3) whereas, most polymeric derivatives of the bishaloaromatics (9a-f), especially those with PFB as comonomer, were insoluble. Inherent viscosities ranging from 0.1 to 0.7 were obtained for soluble polymers. Coherent films could be either solution cast or melt pressed for a number of polymers. 

In the case of insoluble bis-4,4 -disubstituted perfluorobi-phenyls the reaction mixtures were poured into ca. 100 ml of H2O. The insoluble material was collected by filtration, and washed successively with H2O, EtOH and CH2C12 The crude products were dried (vac. oven at 80 ) and twice sublimed for purification. The model products were characterized by IR (neat liauid or KBr), mass spectrometry, and elemental analyses. and "f-NMR spectra we determined for all soluble products. Only minor modifications of this procedure were necessary with different haloaro-matics or nucleophiles. For reactions of potassium phthalimide no K2CO3 was used or needed. 

Fig. 2 Solid state F-NMR spectra of GS-3/3 in oriented DMPC bilayers, measured at 25 °C according to published procedures [17-19,22]. Samples are prepared with a peptidedipid molar ratio of 1 80 (A), 1 40 (B), and 1 20 (C). The arrows indicate the signals emerging at high peptide concentration, corresponding to a new re-aligned state of the peptide. The dashed line shows respective powder pattern of the lyophUized peptide...

Fig. 9 F-NMR spectra of 0.4 mg GS-3/3 each, reconstituted at a peptidedipid ratio of 1 40 in short acyl chain-length DLPC bilayers (A), medium chain-length DMPC (B), and long-chain DPPC (C). Each temperature series encompasses the phase transition of the respective hpid Resonances corresponding to the new upright peptide alignment are highlighted by boxes...

It has been established by a variety of techniques that aromatic cyanate esters cyclotrimerize to form cross-linked cyanurate networks. Analogously, the fluoromethylene cyanate monomers cure to cyanurate networks. In addition to the F-NMR spectra shown in Figure 2.3, evidence includes an up-field shift of the methylene triplet (IH-NMR, 0.21 ppm C-NMR, 9.4 ppm), the disappearance of the cyanate functional group (IR, 2165 cm C-NMR, 111.9ppm) and the appearance of the cyanurate functional group (IR, 1580 and 1370 cm C-NMR, 173.6 ppm). Typically, monomers are advanced to prepolymers by thermal treatment at 120 C or just above the melting point. The prepolymers are then cured at 175 C and are postcured at 225°C. 

Figure 2.3. Schematic "F-NMR spectra illustrating effects of (a) fluoromethylene chain length on monomer resonances and (b) chemical transformation of cyanate functional group on fluoromethylene resonances of n = 6 monomer.

The monomer silane diol (5) was prepared by hydrolysis of the bis-chlorosilane (4) in the presence of sodium hydrogenocarbonate NaHCO at reflux of diethyl ether for 24 h. The hydrolysis was quantitative. The silane diol (5) was characterized by IR, where a narrow band at 3690 cm and a wide band between 3650 and 3050 cm were observed, respectively, for free t)=siOHand bonded t)= aoH Us H- and F-NMR spectra exhibited the expected signals and its Si-NMR spectrum showed a singlet at -i-16.4ppm characteristic for a 5 = siOH and no trace of the starting chlorosilane at -i-31 ppm. ... 

Fig. 11. Changes In gated NMR spectra during the cardiac cycle. Top panel isovolumic left ventricular pressure In a ferret heart paced at 0.99 Hz in 8 mM [Ca +]. NMR spectra were acquired at the two times indicated on the pressure record (a) 10 ms prior to stimulation (b) 75 ms after stimulation. Middle panel shows gated F NMR spectra (each from 800 acquisitions) recorded at (a) and (b), as indicated. The bound (B) and free (F) peaks of 5F-BAPTA exhibit distinct chemical shifts at approximately 8 and 2 ppm, respectively, downfield from a standard of 1 mM 6-Ftryptophan at 0 ppm. It appears that the free [Ca +] varied during the cardiac cycle. Bottom panel shows gated P spectra (400 scans) acquired at times a and b in the same heart. The major peaks correspond to phosphocreatine (0 ppm), ATP (the three peaks upfield from phosphocreatine), and inorganic phosphate (the small peak at 4-5 ppm) (Reproduced from Marban et al. Circ. Res. 1988 63 673-678 [311] with permission of Lippincott, Williams Wilkins).

Fig. 14. Detection of -galactosidase activity in cells using F NMR. Sequential F NMR spectra of LNCaP C4-2 prostate cancer cells transiently transfected with lacZ (1.0 x 10 ) in phosphate buffered saline (PBS) (0.1 M, pH = 7.4, 700 ml) at 37 C following addition of GFPOL (1.84 mg, 5.27 mmol). F NMR spectra were acquired in 102 s each, and enhanced with an exponential line broadening 40 Hz. In each spectrum, GFPOL occurs on the left with liberated FPOL aglycon appearing at right ( ).

Fig. 47. In silu study of a-methylstyrene hydrogenation in a fixed bed of Pd/ALO catalyst, (a) Schematic representation of the bed and the chosen axial bar. (b) A mixed spatial-spectral 2-D map which corresponds to that axial bar. (c) The distribution of the liquid phase along the axial bar obtained as an integral projection of (b) on its vertical (coordinate) axis, (d f) NMR spectra of the liquid phase at various heights along the bar obtained as horizontal cross-sections of the map in (b). The location of these cross-sections is indicated in (b,c) with horizontal lines. Each spectrum corresponds to a volume of 0.66mmx 1.3mmx 2mm. The two vertical dotted lines are drawn to show the differences in relative positions of the external peaks in the spectra. Reprinted from reference (69) with permission from Elserier, Copyright (2004).

Figure 14.9. F-NMR spectra of 10FEDA/4FMPD cured in nitrogen to 70, 120, 150, and 200°C...

Figure 17.2. F-NMR spectra of 6FDA based model compounds (a) 6FDA (b) 6FDA/AN DAA (c) 6FDA/AN, and (d) 6FDA TA (Reprinted from C. D. Smith et al., Polymer 34, 4852-4862. Copyright (1993), with kind permission from Elsevier Science. Ltd., The Boulevard, Langford Lane, Killington 0X5 1GB, UK).

For nonquantitative -C-NMR techniques, this could be the extent of the analysis possible. However, the combination of F-NMR with C-NMR allowed us to quantitatively calculate the isomer composition and to investigate solvent effects on isomer formation. Figure 17.5 illustrates these concepts. Two possible isomers (structures in Figure 17.5) can be formed from the reaction of 3-fluorophthalic anhydride with 4-fluoroaniline. Upon formation of the amic acid based on 3-fluorophthalic anhydride with 4-fluoroaniline, two isomers were found in both NMP and chloroform reactions as shown by the F-NMR spectra in Figure 17.5a and b, respectively. Two signals were observed for each type of fluorine atom, labeled as Fi and F2 for the anhydride and amine fluorine atoms respectively. Ortho and meta isomers were formed in a ratio of 4.75 1 in solution in NMP, while the same ratio was 1.04 1 in chloroform, where the product precipitated. The major isomer was the ortho in each case as determined by C-NMR of the chloroform prepared amic acid (Table 17.1). 

Figure 17.6. Effect of synthetic solvent on the hexafluoroisopropyl region of the F-NMR spectra for 6FDA/4-FA prepared in (a) NMP (b) DMSO, and (c) m-cresol.

As shown in Table 17.3 and Fignres 17.6 and 17.7, the other polar solvents yielded significantly different spectra. For the amic acids prepared in DMSO and m-cresol, the 6F region was essentially identical to the NMP-prepared sample however, for the aromatic regions, fonr peaks were observed instead of two. The strnctnres in Table 17.3 can aid in this discnssion. Each of the p,p- and m, m-isomers shonld yield one signal in the F-NMR spectra since the aryl fluorine atoms on all of these molecules are equivalent. For the m,p-isomer, the two fluorines are not chemically equivalent to each other and should thus yield two peaks. 

Figure 17.8. F-NMR spectra PMDA based 4-FA model compound prepared in NMP...

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