Spectra of Other Nuclei

Spectra of Other Nuclei.—Data obtained for l-substituted-4-/7-fluorophenyl-bicyclo[2,2,2]octanes contradict the usual viewpoint that the field effect is relatively unimportant in determining the magnitude of aryl F substituent chemical shifts (FSCS). ° The FSCS are found to be significantly dependent upon substituent polarity (ff,), and are well fitted by a dual substituent parameter equation in the form FSCS = - xa, — yOg, where the values of x and y depend upon the n.m.r. solvent (C H or DMF) employed. 

The molecular structures of a-, p, and y-chlordene (components of technical chlor-dane) have been determined from C1 n.q.r. and other spectral data. The C1 n.q.r. frequencies of a variety of pairs of cis- and trans-isomers of chloroethylenes (including the incorporation of this structural unit into bridged bicyclic molecules) indicate that cis-substituents produce measurably greater shifts than do trans-substituents.  

Fujikura, K. Aigami, N. Takaishi, H. Ikeda, and Y. Inamoto, Chem. Letters, 1976, 507. 

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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 No 13C studies have appeared so far (however, some unpublished measurements on type B systems have been made185b 435, 437). 

Although the proton is the most extensively studied nucleus, NMR spectra of other nuclei have been investigated. 

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... 

For an accurate quantification of the content of substructures, it is essential that the NMR spectra are recorded under appropriate experimental conditions. In general, two effects can falsify the signal intensities (i) an incomplete spin-lattice (Ti) relaxation and (ii) a heteronuclear Overhauser effect, resulting from H decoupling. Typically, the NMR signal quantification is less crucial from the proton spectrum than from spectra of other nuclei, which require the correct choice of experimental conditions. To date, very few relaxation studies have been reported comparing data for terminal, linear, and dendritic units. Longer Tm values were... 

The emphasis in this book is on the broad approach to structural problems, to use as many techniques as possible to elucidate the structural properties of a compound. In the same way, it is often valuable to apply a single spectroscopic method widely, and obtain more information than is given by a single spectrum alone. Too often we are content to run a proton NMR spectrum and puzzle over its interpretation, when spectra of other nuclei could resolve the problem quickly and easily. The analysis of the spectmm shown in Figure 4.39 is not at all difficult when it is taken in conjunction with F and P NMR spectra. Once the magnitudes of two of the coupling constants have been determined, the others quickly follow. Moreover, the various spectra, taken together, provide sufficient information to enable the compound to be completely identified. 

Important, however, is the contribution, [jtri( Pt)] , made to the width of Pt satellites in the spectra of other nuclei. Although this is less than the broadening of the Pt spectrum, it is proportionately greater when compared to the normal... 

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