Charge-NMR Shift Correlations

Atomic Charges, Bond Properties, and Molecular Energies, by Sandor Fliszar Copyright 2009 John Wiley Sons, Inc. 

For the benzenoid sp carbons, one must consider the variations of both the a and 7T electronic charges, = niAq, so that Aqc = Aq. + Aq = (m+ l)Aq, with ASc = 157A hence 

The slope (157) is expressed here in ppm/electron, with Aq and Aqc in electron units. Reverting now to millielectron units, we get 

The N-15 resonance shifts of alkylamines and nitroalkanes are expressed in ppm from HNO3, in methanol. Separate correlation lines are observed for mono-, di- and trialkylamines, namely 

The correlations involving 0-17 atoms concern dialkylethers, alcohols, aldehydes, and ketones. For the dialkylether oxygen atoms, the appropriate formula is 

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For example, the charge-NMR shift correlation [Eq.(5.9)] gives n=— 4.4122 for p = 30.12 me. Using this result and the formula given for the methane carbon atom (Table 5.2), we get the useful formula... 

Selected empirical best fit reference charges are reported in Table 5.6. The results for nitrogen and oxygen are described in Part III, as are the relevant, highly accurate charge-NMR shift correlations. 

Alkane carbon atoms satisfy the charge-NMR shift correlation [Eq. (6.8)]. With the alkylamines, things could be different because of a possible extra effect due to the presence of the nitrogen atom a-carbons should perhaps be compared only among themselves, and so should the /3- and y-carbons. The S-carbons, in contrast, which are sufficiently separated from the nitrogen center, could probably be treated as if they were part of an alkane. This point has been examined as follows for the —C 2—H2—NH2 motif, focusing on the dissociation and intrinsic bond energies, Dc Cp and sc Cp, respectively. 

The validity of this approximation is best illustrated by the results offered in Table 16.5. Although Eq. (16.4) permits accurate calculations of atomization energies and represents a simple and valuable tool, it must be made clear that the charge-NMR shift correlations used for the atoms of the carbonyl group (i.e., those involved in the A j Sca and A460 terms) are empirical. On the other hand, it turns out that for the ketones A j 8ca +A460 amounts to less than 5% of kAqk- Hence, with... 

Smaller or larger cycles are not described by this formula their appropriate charge-NMR shift correlations are yet to be investigated in a systematic fashion, as well as other possible effects that may be due to changes in hybridization. 

It has already been said that the merits of a method for charge calculation can be assessed mainly by its usefulness in modeling experimental data. Charges from the PEOE procedure have been correlated with Cls-ESCA shifts [28], dipole moments [33], and NMR shifts [34], to name but a few. 

Chain processes, free radical, in aliphatic systems involving an electron transfer reaction, 23,271 Charge density-NMR chemical shift correlation in organic ions, 11,125 Chemically induced dynamic nuclear spin polarization and its applications, 10, 53 Chemiluminescence of organic compounds, 18,187... 

Ionic dissociation of carbon-carbon a-bonds in hydrocarbons and the formation of authentic hydrocarbon salts, 30, 173 Ionization potentials, 4, 31 Ion-pairing effects in carbanion reactions, 15, 153 Ions, organic, charge density-NMR chemical shift correlations, 11,125 Isomerization, permutational, of pentavalent phosphorus compounds, 9, 25 Isotope effects, hydrogen, in aromatic substitution reactions, 2,163... 

Charge density-NMR chemical shift correlation in organic ions, 11, 125... 

The obtained STPP liposomes were characterized by size distribution analysis, P NMR spectroscopy (Fig. 3), and by zeta potential measurements (Fig. 4). The size of liposomes with 20 mol% incorporated STPP was determined to be 132 zb 59 nm, which did not change significantly upon storage at 4°C over several days. The P NMR spectrum of STPP liposomes shows two chemical shifts correlating to the phosphorus in the lipid s phosphate groups and to the positively charged phosphorus of STPP. No differences in both chemical shifts between the free compounds (i.e., free STPP and free... 

Charge Density-NMR Chemical Shift Correlations in Organic Ions... 

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