Resonance of Other Nuclei

The F nmr spectra of the fluorine-substituted oxiranes have been reasonably well studied, for in the region of high chemical shifts, the fluorine nuclei readily yield spectra that can be interpreted directly. A further principle is that the long-range coupling constants can be measured well because of the large nature of the constants.In the case of a fluorinated substituent, the linear Taft correlation may be used to determine the inductive and resonance substituent constants.  

The resonance of the C nuclei may be employed extremely well in studies of oxirane structures. From the C spectra for 61 oxiranes an additivity rule was formulated for the chemical shifts. Some examples are given in Table 5. 

The conformation of cycloheptene oxide has been examined via the C nmr spectra of deuterated compounds on the basis of the temperature-dependence of the chemical shifts of the individual signals. In phenyl-substituted oxiranes, the C shifts have revealed the inductive and hyperconjugative effects of the oxirane ring, and thus the ring behaves as an electron-acceptor.  

From the nmr data on 42 aliphatic oxiranes, an additivity relationship has been derived for calculation of the chemical shifts. An nmr investigation has been described on the addition products of indene derivatives and singlet oxygen. Good reviews of the nmr data may be found in the following references and in the papers cited therein.  

Exo and endo oxiranes of bicyclo[2.2.1]heptane can be well differentiated on the basis of their spectra.The effect of the molecular asymmetry on the chemical shift of the carbon in 0- and A -glycidyl compounds has been investigated. In the study of stereoisomeric epoxyspirocyclohexane derivatives, the effects of the equatorial and axial oxiranes have been observed on the carbon atoms of the cyclohexane ring.  

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The technical difficulties of observing the resonance of other nuclei are often deterring and an elegant solution may be found in the INDOR... 

H NMR spectrometry is the foundation upon which we will build an understanding of the magnetic resonance of other nuclei, especially 13C, which leads to the important advanced correlation experiments. We began by describing the magnetic properties of nuclei, noting the special importance of spin 1/2 nuclei. For practical... 

Equation (2) is still difficult to handle since it contains the quantity D as well as the two numbers which we wish to determine, 0 and r. If we select a resonance shift of a given nucleus and ratio all shifts of resonances of other nuclei in a given molecule to it, then in the ratios D disappears. Thus for a rigid frame ligand there is the immediate possibility of carrying out a search for the exact geometry of the frame relative to the... 

Virtually all published work refers to proton magnetic resonance studies, though spectra of other nuclei are beginning to be examined. No 13C studies have appeared so far (however, some unpublished measurements on type B systems have been made185b 435, 437). 

The resonance of a nucleus may be affected by the proximity of other nuclei in the molecule whose spins are non-zero these need not be of the same atomic number as the nucleus under scrutiny. Suppose we have two nuclei A with a spin IA and B with a spin /B. The resonance of nucleus A will be split into (2/B + 1) peaks, equally spaced and of equal intensity this happens because the precise frequency at which A absorbs depends upon the magnetic state of B. Because the (2/B + 1) states are so close in energy, they are for most practical purposes, equally occupied hence the equal intensities of the peaks in the resonance of nucleus A. The spacing between the peaks is the coupling constant J between the nuclei. This is expressed in frequency units the coupling constant is independent of the operating frequency of the spectrometer, in contrast to the chemical shift. If the nuclei A and B are chemically remote, the coupling may be so small that it cannot be observed. This is usually the case if the nuclei are separated by more than about three bonds in the molecule. 

The first Chapter on nuclear magnetic resonance2 in this Series was devoted principally to p.m.r. spectroscopy, because, up to 1964, virtually no magnetic resonance studies of other nuclei in carbohydrates and their derivatives had been made. The present Chapter is also concerned mainly with the p.m.r. technique, in the expectation that the broad subject of nuclei other than protons will be treated separately in this Series. 

NMR spectra of other nuclei have been reported. A problem with NMR is the broadness of the signal because of the adjacent nitrogen atom isothiazole absorbs at -1-53.7 ppm (reference (NH4)2S04) <84CJC98I >. The saccharinate anion has been examined by O NMR the chemical shifts for 0-1 (155 ppm) and 0-3 (275 ppm) (reference H2O) are consistent with extensive contribution from resonance forms such as whereas the sulfur oxygens show little evidence for... 

Sodium is unlike any other cation in its charge and radius. Thus, sodium must be followed by its own nuclear properties (18). Potassium can be replaced, in principle, by thallium(I) and cesium. Both are useful as they have suitable nuclei for NMR studies but thallium has additionally an absorption band at 214 nm which is very ligand-dependent, a readily observable fiuorescence, and a small temperature-independent paramagnetism which can cause marked shifts in the nuclear resonances of ligand nuclei. We (19) have aimed in the first instance to discover if thalhum replaces potassium eflFectively in enzymes. Table VII shows that it does. 

The bombardment of B with protons creates a compound nucleus, with an excitation energy of about I6 MeV, and as in the case of other nuclei of mass (An — 1), many resonance phenomena are observed. The elastic scattering reaction is under investigation, but full results have not yet been reported the inelastic scattering from low states of B was observed by Fulbright and Bush and by Cowie et al. [34], but the resonant features were not studied by... 

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