Deshielding 318 Subject

The protons ortho and para to the nitro groups are subject to downfield shifts attributable to mesomeric effects ortho protons also experience a large proximity effect resulting in further deshielding. 

Walters Options The Alternative Cancer Therapy Book (1993) contains a short introduction to the subject under the section Metabolic Therapies, with the statement that proteolytic (protein-digesting) enzymes are believed to dissolve the walls of cancer cells, and that enzyme treatments are widely used in Europe. More specifically, enzymes are used variously in what are called Issels therapy, in Wheatgrass therapy, in the Gerson diet, in Kelley s therapy, and in Niepa- s therapy (Walters, 1993, pp. 86,147,198,207,216). It is noted furthermore that chranotherapy destroys the body s enzymes, that cooking destroys the enzymes in food, and that enzymes may be involved in the so-called spontaneous remission of cancer (Walters, 1993, pp. 155,201). Also noted, in the work of Hans Niepa-, is that the enzyme bromelain, derived from pineapple roots, will deshield cancer cells, as will beta-carotene (Walters, 1993, p. 222). 

The chemical shift of the 19-methyl is subject to the influence of 5,6- or 6,7-epoxides as well as the presence of the 4B-hydroxyl and the presence of B-unsaturated system or saturated -l-)ceto system in ring A. In the case of 6a, 7o-epoxides the 19-methyl generally comes around B1.20 while the same comes around 6 1.30 in 56,66-epoxides because of the deshielding influences of the 66-epoxy oxygen on the 19-methyl in the latter. In agreement with this the 19-methyl moved downfield to 6 1.32 in... 

Graphite surface (in particular, EG surface) contains a lot of structural imperfections, such as oxidized groups and residual molecules of oxidizers (Morimoto and Miura 1985). They can be involved in formation of H-bonded complexes with water-type molecules. Active protons in such associations should be subjected to a deshielding effect of electron-donating atoms, and, besides, in this case, one could expect the appearance of H NMR signals with down-field shift relative to the corresponding resonance lines for a condensed phase. As no such peaks were found in the spectra, and, in addition, experimentally determined chemical shifts for water are close to calculated values, it may be concluded that the concentration of these sites in EG is low in comparison with hydrophobic adsorption sites on basal graphite planes of a carbon surface. 

Why is deshielding so pronounced for alkenyl hydrogens Although the electron-withdrawing character of the p -hybridized carbon is partly responsible, another phenomenon is more important the movement of the electrons in the ir bond. When subjected to an external magnetic field perpendicular to the double-bond axis, these electrons enter into a circular motion. This motion induces a local magnetic field that reinforces the external... 

Orientivity at C-9 was established from the 511d H-NMR data which failed to indicate a shielding effect of the C-9 carbomethoxy group on the C-5 methyl. An a-oriented carbomethoxy group would have a 1,3-diaxial relationship with the C-5 methyl which would then be subject to deshielding. The absence of deshielding indicated a /3-oriented sidechain and an ol-oriented methyl at C-9. 

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