3IP Chemical shifts

The 3IP NMR chemical shifts, shown in Table IV, should be a useful indicator of the electronic environment at phosphorus. Almost all the 3IP chemical shifts are upfield (negative 8 values) in contrast to the boron-phosphorus compounds where downfield shifts (positive 8 values) are observed. This can be interpreted in terms of weak gallium-phosphorus it-... 

Assignment of the NMR signal was made comparing 3IP chemical shifts of initial and final compounds. 

Notably, 161 and 163 have different 3IP chemical shift values. The anions of these molecules have different spatial structures. A H and 3IP NMR study showed that the anion of 161 adopts a twist conformation, whereas 163 exists in a chair conformation with an equatorial phenyl at the phosphorus atom. Thus, ion exchange reactions are stereospecific. 

Complexes with silver nitrate are also obtained, the number of ligands depending on the ratio of reagents [Eq. (156)]. Notably, the 3IP chemical shift changes from -20 to 0 ppm on addition of silver nitrate to bis(oxy-methyl)phenylphosphine. This change probably results from the coordina-... 

Fig. 6. 3ip Chemical shifts and s—p sigma orbital populations in compounds PR4 and PR3 calculated according to the method of Letcher and Van Wazer (13)...

The nucleus 31P is useful in determining the micellization processes of phosphorus-containing surfactants. For the lithium ethyl (n-octyl) phosphate in D20, a critical micelle concentration was determined by 3IP NMR spectra.54 Three CMCs were detected by the inflection points in the concentration-dependent slopes of the 3IP chemical shift of a soybean phosphatidylcholine in n-butanol. They are 7.5%, 35% and 63% w/w soybean phosphatidylcholine.-55... 

Figure 2 Influence of the C-substituents on the 3IP chemical shifts of diphosphiranes.

The details of 3c, iR and 3 Ip n.m.r. spectra for a range of carbamoylmethylphosphine oxides have been reported. From this data a correlation between 3ip chemical shift and the nitric acid extraction constant has been determined. 

Metal-Phosphorus Bono Lengths, Torsion Angles between the Metal and Phosphorus Coordination Planes, Sums of Angles at Phosphorus, and 3IP NMR Chemical Shifts for Three-Coordinate Aluminum, Gallium, and Indium Phosphides... 

The derivatives 15a-i exhibit characteristic 31P NMR spectroscopic data (see Table I), which are distinctly different from those observed for the P-organo-substituted derivatives 12 and 13 (8(3IP) = 65.8-136.0).27 However, the similar Si chemical shifts and. /(Si, P) coupling constants observed for 12,13, and 15 clearly show the identical electronic nature of the low-coordinate silicon centers in these derivatives. 

R = H, X = S, A = Et3N and Py). In solution the former is mainly in an ionic form the latter exists as a complex. The basicity of the amine is assumed to be important. Triethylamine is a stronger base than pyridine and the ionic form is stabilized. When the proton affinity is weak, the basicity in relation to the B(III) atom, a Lewis acid, plays an important role. This involves an equilibrium shift toward the complex. This assumption is confirmed by an easy displacement of pyridine by triethylamine. The reverse process demands more severe conditions. In the NMR spectra of the triethylamine complex the signal is shifted from 22 to 42 ppm as pyridine is added. The absence of signals of two separate forms is evidence in favor of their fast interconversion. The chemical shift of the signal in 3IP spectra is 22 ppm (EtOH), 26 ppm (Py, DMFA), and 42 ppm (EtOH, Py) for complexes with triethylamine and pyridine. 

On studying a series of ammonium 1,3,2,5-dioxaborataphosphorinane oxides (111), the dependence of the tautomeric equilibrium position on amine basicity was analyzed. The equilibrium position was estimated from chemical shift values of bis(oxymethyl)phenylphosphine oxide with 8 3IP of 35 ppm being used as a model of an acyclic form and 5-Ph-5-oxo-1,3,5-dioxaphosphorinane (107, R = H) with 8 3IP of 6 ppm used as a model of a cyclic compound. The chemical shift values (111, X = 0, R = H) and dissociation constants (pKa) of conjugate acids for amines are presented in Table V. 

Molecule (126) possesses an unusual chemical shift in its 3IP NMR spectrum (8 31P 12,5 ppm in THF, C6H6, DMFA), significantly different from that of similar tertiary phosphines, eg., diphenylbenzylphosphine (-10 ppm) and oxymethyldiphenylphosphine (-14 ppm). However, the chemical shift of compound 126 in pyridine is -4 ppm. An analogous effect was described for borylphosphine ethene (see Section V) here an intramolecular dative P—B bond is cleavaged in pyridine due to the formation of complex. The chemical shift changes from 10 ppm to -4 ppm. 

It is clear that NMR spectroscopy could be used to detect certain nuclei (e.g. H, i9p, 3ip) and, also to estimate them quantitatively. The real usefulness of NMR spectroscopy in chemistry is based on secondary phenomena, the chemical shift and spin-spin coupling and, to a lesser extent, on effects related to the time-scale of the NMR experiment. Both the chemical shift and spin-spin coupling reflect the chemical environment of the nuclear spins whose spin-flips are observed in the NMR experiment and these can be considered as chemical effects in NMR spectroscopy. 

Quantitative Correlation of 3IP NMR Chemical Shift Changes on Conversion of Phosphines to P(IV) Derivatives... 

The characteristics of the water pool of reverse micelles has been explored by H, 23Na, 13C, 3IP-NMR spectroscopy. Since the initial association process in RMs is not totally understood, and because of the low CMC, aggregation studies from NMR are rather scarce. Direct determination of a CMC in the diethyl hexyl phosphate /water/benzene system (at Wo = 3.5) was possible because the chemical shift of 31P in phosphate groups is very sensitive to hydration effects. The structure and state of water in RMs and particularly at low water content has received considerable attention. The proton chemical shifts have been explored in AOT/water/heptane, methanol, chloroform, isooctane and cyclohexanone. The water behavior in small reverse micelles is close to that of the corresponding bulk ionic solution. Until now, the effect of a solute on micellar structure was not well... 

The result, in the absence of other nuclei such as 2H, 3IP, 19F, is a sharp peak for each chemically nonequivalent carbon in the compound, except for the infrequent coincidence of 13C chemical shifts. See Figure 4.1b for the ll decoupled 13C spectrum of cholesterol and compare... 

These isomers and all a-thionucleotide diastereomers can be conveniently distinguished by 3iP-NMR spectrometry, as shown by Sheu et al. [23] and also by Jaffe and Cohn [38]. The Pa chemical shifts for the diastereomers of a-thionucleotides differ by 0.25-0.4 ppm, (Rp) upfield, and similar differences exist between the diastereomers of ATP/JS. 31P-NMR is probably the most positive way of assigning configuration to these nucleotides. This is because the enzymes often do not exhibit absolute specificity for one or the other isomer, and a false positive result can be obtained if too much test enzyme is used with an unknown. A typical set of spectra for a mixture of a-thionucleotides is given in Fig. 12. 

Suppose that the 3IP spectrum acquired in review problem 3.2 exhibits two signals, one at 6396 Hz downfield from the reference compound and the other at 3937 Hz upfield from the reference compound, (a) What is the reference compound (b) What is the chemical shift in ppm for each of the above signals ... 

IP H NMR Chemical shifts of tetraalkylphosphonium ions formed by traping of model cations or macrocations135... 

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