Chemical-shift measurement

First P nmr chemical shifts measured by W. C. Dickinson (for POCh. PCl., etc. relative to aq. H. POa) Detergents (using polyphosphates) overtake soap as main washing agent in the USA. (Heavy duty liquid detergents with polyphosphates introduced in 1953.)... 

A method for determining the basicities of phosphoryl compounds has been decribed which is based on 31P n.m.r. chemical shift measurement and a two phase system consisting of an organic solvent and 12H sulphuric acid.245 The gas-phase protonation of aliphatic phosphine oxides have been determined by cyclotron resonance. There was a good correlation of pK4 with Kabachnik constants and HO... 

In NMR spectroscopy, however, the chemical shift measurement we make takes place in an environment of our making that is both entirely artificial and arbitrary (i.e., the magnet ). For this reason, it is essential to reference our measurements to a known standard so that we can all speak the same language, no matter what make or frequency of spectrometer we use. 

The 15N chemical shifts measured for the Schiff base being a derivative of gossypol [7] and L-phenylalanine methyl ester equal —243.7 ppm in CDC13 solution and —237.5 in solid state (relative to external... 

The hydration state of lanthanide(III) chelates can be assessed by different techniques. Luminescence studies are widely used for Eu111 and Tb111 chelates (see Chapter 9.21).17 18 170 NMR chemical shift measurements in solution of lanthanide(III) (most often Dy or Gd) complexes can also give information on q.19 These techniques in the context of MRI contrast agent research have been reviewed in 2001.1... 

Have you wondered about those funny curves drawn over the NMR peaks They re electronic integrations and they can tell you how many protons there are at each chemical shift. Measure the distances between the horizontal lines just before and just after each group. With a cheap plastic ruler I get 52 mm for the benzene ring protons, 21 mm for the —CH2— protons, and about 30 mm for the —CH3 protons. Now you divide all the values by the smallest one. Well, 21 mm is the smallest, and without a calculator I get 2.47 1 1.43. Not even close. And how do you get that 0.47 or 0.43 proton Try for the simplest whole number ratio. Multiply everything by 2, and you ll have 4.94 2 2.86. This is very close to 5 2 3, the actual number of protons in ethylbenzene. Use other whole numbers the results are not as good and you can t justify the splitting pattern—3 split BY 2 and 2 split BY 3—with other ratios. Don t use each piece of information in a vacuum. 

Structure elucidation of three related derivatives of ring system 2 ( temozolomide 9a, mitozolomide 9b, and the related acid derivative 9c) has been carried out by 13C and 15N NMR spectroscopy <1995J(P1)249> (Scheme 2). The 1SN NMR chemical shifts measured in dimethyl sulfoxide (DMSO) solutions are listed in Table 1. For compound 9a, Lowdin charges of the nitrogen atoms have also been calculated and found to have a linear relationship with the experimentally determined chemical shifts of these atoms. The NMR data of 9a have been correlated with those of a series of heterocycles of related structure by the same team <2002MRC300>. 

McDermott, A. Ridenour, C. F. Proton chemical shift measurements in biological solids in Encyclopedia of Nuclear Magnetic Resonance, Grant, D.M., Harris, R.K. (eds.), 1996, pp 3820-3825. 

Recently262, the apparent stability constants of the complexes between aromatic fluoro derivatives and amines (shown in equilibrium 31, Kc in moL1 dm3) in toluene- were evaluated by 19F chemical shift measurements. 

The 13C, 29Si and 119Sn NMR chemical shifts measured for stannylallenes and silylstan-nylallenes are presented in Tables 44 and 46 "/(119Sn13C), "/(119Sn117Sn), "/(29Si13C) and isotope shifts (IS) are given in Tables 45 and 46. 

The chemical shift measured on the bulk water signal and normalized by the mole fraction of bound water, Pm, is given by Eq. (10), where m and mA are the observed chemical shifts with and without the paramagnetic compound and ffios is the shift originating from water molecules outside the first coordination shell. 

C NMR measurements were performed on Varian CFT-20 and XL-100 spectrometers under conditions which have been described previously (,1 0). C chemical shifts are reported with respect to external tetramethylsilane (TMS). Dioxane was added to the samples as an internal standard for linewidth and chemical shift measurements. 

Since atoms in different environments experience different chemical shifts, measuring the chemical shift can give information about the local environments of the atoms. The measurements can be interpreted empirically but in many... 

Estimates of the percentage ee conformation in other V,/V-dialkylhexahy-dropyrimidines are given in Table XXVI. Some disagreement exists between the positions of equilibria for the Af,Al-diisopropylhexahydropyrimidine based on dipole moment and on H-NMR chemical-shift measurements but in this case the higher (dipole moment) value is probably more representative of the true state of the equilibrium. 

Some attempt has been made to establish relationships between chemical shifts, measured by nuclear magnetic resonance spectroscopy and redox potential data.42... 

In addition to line broadening due to accelerated relaxation, paramagnetic salts and chelates give rise to isotropic shifts when added to samples containing molecules with groups susceptible to coordination with metal ions, e.g. —OH, —NH2, — SH, — COOH, -C = 0. The isotropic shift A of a nucleus i in a sample S is the difference between chemical shifts measured before and after addition of the paramagnetic shift reagent SR [103] ... 

Formyl complexes are characterized by distinct spectroscopic features. The most frequently used diagnostic probe has been H NMR. Chemical shifts in the 8 12-17 range (several ppm downfield from normal aldehyde or formamide H-NMR resonances) (69) are observed. However, since chemical shifts measured in the presence of trialkylborane by-products can show marked temperature dependence (32, 38, 47, 66), absolute values must be treated with caution. 

The synthetic route (c) was recently utilized to prepare unsaturated monomers containing the hexacoordinate silicon unit, followed by polymerization to form novel polymers with hexacoordinate silicon in the polymer chain (equation 49)214. The29Si chemical shift measured in the polymer solution (ca —60 ppm) is very similar to that of the monomer (—63.8 ppm), and is evidence for hexacoordination in the polymer solution. 

Abbreviations calor = AH obtained from integration of the integrated DSC curve vH - a van t Hoff enthalpy obtained from UV absorbance or NMR chemical shift measurements unless otherwise noted NR indicates that results were not reported. 

The presence of contact relaxation indicates that a given moiety is covalently bound to a paramagnetic metal ion and provides an estimate of the absolute value of A (Eqs. (3.26) and (3.27)). Sometimes the contact coupling constant can be evaluated by chemical shift measurements, and it is therefore possible to predict whether the contact relaxation contributions to R m, Rim or both, are negligible or sizable. 

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