Interpretation of NMR Spectra

At first glance splitting may seem to complicate the interpretation of NMR spectra In fact It makes structure determination easier because it provides additional information It tells us how many protons are vicinal to a proton responsible for a particular signal With practice we learn to pick out characteristic patterns of peaks associating them with particular structural types One of the most common of these patterns is that of the ethyl group represented m the NMR spectrum of ethyl bromide m Figure 13 15... 

The introduction of a THP ether onto a chiral molecule results in the formation of diastereomers because of the additional stereogenic center present in the tetrahy-dropyran ring (which can make the interpretation of NMR spectra somewhat troublesome at times). Even so, this is one of the most widely used protective groups employed in chemical synthesis because of its low cost, the ease of its installation, its general stability to most nonacidic reagents, and the ease with which it can be removed. 

Conformational shift effects could be discussed in terms of discrete rotational isomeric states. Mainly two effects could be derived empirically to explain the shift differences due to conformational isomerism they-gauche and the Vg effect. However the spectra also indicate that the y-gauche effect is not a quantity with a universal numerical value. Furthermore the spectra of the cycloalkanes show that the conformational effects do not obey simple rules of additivity. With concern to our present knowledge great care has to be taken for the interpretation of NMR-spectra on the base of conformational shift increments which were not determined for the specific molecular structures. 

Englert O published the best and greatest compilation of chemical shifts of carotenoids, including some isomers, which are essential for interpretation of NMR spectra. 

As we ve mentioned before, the interpretation of NMR spectra is often made complex by the sheer quantity of information that you are confronted with. This is every bit as true for carbon NMR as it is for proton and when you combine the two, that huge pile of information just gets bigger... More important still then that you approach the pile in a logical, methodical manner. 

Low-molecular weight stars were prepared to facilitate the interpretation of NMR spectra. Figure 3 shows the NMR spectrum of a virgin sample indicating resonances at 6=1.95 and 6=1.65 ppm, characteristic of protons of the terminal -CH2-C(CH3)2-C1 group [65]. The absence of resonances at 6 4.6 and 6-4.8 ppm, characteristic of terminal unsaturation, also suggests that the arms carry tert-Cl end groups. 

Interpretation of NMR spectra is subject to the same types of errors encountered in other spectroscopic analyses. There are, however, several pitfalls unique to NMR that may not be avoided if all the factors that can affect resonance-line shape are not clearly understood. These factors are considered here to emphasize the need for care in interpretation. 

Interpretation of NMR spectra depends on the concept of chemical-shift equivalence, an understanding of which depends on stereochemical concepts these are reviewed with special emphasis on interchange through symmetry operations within the molecule, and through rapid structural changes. 

There are a series of aids for the interpretation of NMR spectra of equilibrated redistribution mixtures. Spectra of systems involving equilibria in simple compounds, of course, are easier to correlate than those of families of compounds. 

With some mastery of basic theory, interpretation of NMR spectra merely by inspection is usually feasible in greater detail than is the case for IR or mass spectra. The present account will suffice for the immediate limited objective identification of organic compounds in conjunction with other spectrometric information. References are given at the end of this chapter. 

R. H. Bible, Jr., Interpretation of NMR Spectra, An Empirical Approach, Plenum Press, New York, 1965. 

The basic problem in the interpretation of NMR spectra of humic substances is that for quantitation, as we have pointed out above, the integrated area under a given band in a NMR spectrum is not only a function of the number of carbon atoms resonating at that frequency, but is also a... 

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