Nuclear magnetic resonance data interpretation

The use of theoretical methods in the study of bicyclic systems with P-, As-, Sb-, or Bi- bridgehead atoms has contributed to an increased understanding of the geometry, stability, and ring-strain effects of these systems. In addition, important data relating to basicity and the interpretation of nuclear magnetic resonance (NMR) and X-ray data have been generated. A vast majority of the work done has focused on P. 

Halle, B. and Karlstrom, G. 1983b. Prototropic charge migration in water. 2. Interpretation of nuclear magnetic resonance and conductivity data in terms of model mechanisms. J. Chem. Soc. Faraday Trans. 7/79, 1047-1073. 

We describe in some detail the techniques of nuclear magnetic resonance which are used for studying alumina-supported platinum catalysts. In particular, we describe the spin-echo technique from which the Pt lineshape can be obtained. We also discuss spin echo double resonance between surface Pt and chemisorbed molecules and show how the NMR resonance of the surface Pt can be separately studied. We present examples of experimental data and discuss their interpretation. 

An example of some recent data which was interpreted to support this assumption is the work of Knoeck and Taylor (12). Using PMR spectra of mannitol-boric acid solutions, they observed that a decrease in pH resulted in a decrease in the mannitol-boric acid complex concentration. These results are supported by nB nuclear magnetic resonance (NMR) spectroscopy (16) which showed that the complex between mannitol and boric acid increased with increasing pH. However, Knoeck and Taylor (12) reasoned that since an increase in pH resulted in an increase in the borate anion concentration, as well as an increase in the complex concentration, the diol reacts only with the borate ion to produce the complex. 

One of the principal contributions of electronic data processing over the past several years in terms of chemical analysis is the saving of manual effort in interpreting analytical data. Special techniques, such as Fourier transform, have increased speed (as well as sensitivity) by orders of magnitude in connection with infrared, nuclear magnetic resonance, and mass spectroscopy, Of course, for on-line process analyses, essentially instantaneous interpretation is required to provide the proper error signal that is used to position the final control element (valve, feeder, damper, etc.). 

Spectroscopic techniques, such as ultra-violet (9), Infrared (25), Nuclear Magnetic Resonance (24), and Fluorescence spectroscopies (5-8), constitute direct probes of specific events occurring at the molecular scale. When a quantitative interpretation is possible, spectroscopy provides very detailed microscopic information. Unfortunately however, the interpretation of spectra in terms of molecular events is often complex. Yet another approach that probes events at the molecular scale involves the use of tracers, such as chromophores (1-225). Again, the complexity of the tracer imposes limitations on the extent to which the data can be interpreted quantitatively. 

Basic information on the nuclear magnetic resonance (NMR) properties of pyrroles and their benzo derivatives is collected in CHEC(1984) <1984CHEC(4)155> and CHEC-II(1996) <1996CHEC-II(2)1>. Only recently acquired data or new structurally relevant interpretations of old data based are reported here. 

UV spectra usually involve electronic state transitions, so that simple Hartree-Fock and DFT calculations often are not sufficient PCM has been recently extended also to multi-configurational (MC-SCF) calculations [113] and to time-dependent approaches, allowing for the description of excited states and then the prediction of the so-called solvatochromic effects on these spectra. Nuclear magnetic resonance (NMR) and electron spin resonance (EPR) spectra are even more influenced by solute-solvent interactions moreover, the interpretation of experimental data is often very difficult without the support of reliable ab initio calculation, especially for EPR which is usually applied to unstable radical species. 

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