Group 14 congeners

Table 3.23 summarizes the rotation barriers and leading vicinal cr-cr interactions for methyl rotors CH3—X(X = CH3, NH2, OH) as well as higher group 14 congeners H3M—MH3(M = Si, Ge). Figure 3.59 shows orbital contour diagrams for syn and anti orientations of selected vicinal donor-acceptor NBOs in these species. We now discuss some qualitative trends of torsion barrier potentials in terms of these examples. 

Several of the originally planned chapters, on comparison of silicon compounds with their higher group 14 congeners, interplay between theory and experiment in organisilicon chemistry, silyl radicals, recent advances in the chemistry of silicon-phosphorous,-arsenic,-antimony and -bismuth compounds, and the chemistry of poly silanes, regrettably did not materialize. We hope to include these important chapters in a future complementary volume. The current pace of research in silicon chemistry will certainly soon require the publication of an additional updated volume. 

The Origin of Ring Strain and Conformational Flexibility in Tri- and Tetrasiloxane Rings and Their Heavier Group 14 Congeners... 

Keywords siloxane rings, group 14 congeners, DFT calculations, ring strain, ring puckering... 

Polygermanes and polystannanes are heavier Group 14 congeners of polysilanes (Fig. 8.1). 

As regards the heterometals that, together with gold, form supramolecular entities, there are not very many. It would be tempting to think that the group congeners silver... 

There are now known a eonsiderable number of alkaloids containing two distinct woquinoline nuclei, such as emetine and its congeners (p. 394), and in the morphine sub-group, -morphine, dithebainone (p. 255), disinomenine and its pseudo-isomeride (p. 268). The most important collection of such alkaloids is the bisbenzylwoquinoline or biscoclaurine section of which the following two alkaloids, berbamine and oxyacanthine, are examples, but which is typically developed in the Menispermaceas. 

It has come to be suggested that coplanar congeners as a group express toxicity through a common mechanism interaction with the cytosolic Ah receptor (Safe 1990 Ahlborg et al. 1994) (Environmental Health Criteria 140). Although the full... 

Congener A member of a group of structurally related compounds. 

The 2 -chloro and 2 -bromo congeners of either 748 (FIAC) or 758 (FMAU) are more cytotoxic than FIAC and FMAU, suggesting that these chloro and bromo nucleosides, in contrast to the 2 -fluoro compounds, are comparatively better substrates for deoxycytidine kinase of human lymphocytes than the substrates for viral-specific thymidine kinase. The disposition of the 2 -fluoro group may also be important from the biological viewpoint. It should be noted that the structural difference between RNA and DNA is at the 2 -position. The ribo type of analog (738) of FIAC is 10 times less effective in suppression of HSV replication than is FIAC. Thus Fox, and Watanabe and coworkers concluded that the 2 - up fluorine disposition and the species of the substituent at C-5 are the two important factors influencing antiviral activity. Nevertheless, the mechanism of action of 2 -deoxy-2 -fluorocytidine (737) on certain herpes viruses, including HSV-1... 

Unlike heliantholysin and congeners, the toxicity of metridiolysin is not prevented by sphingomyelin, but is inhibited by cholesterol in low concentration, as well as by certain related sterols (23). In addition, metridiolysin is activated by thiols such as dithiothreitol, and is reversibly inactivated by compounds having an affinity for SH-groups, such as p-hydroxy-mercuribenzoate. A third notable feature is that the action of metridiolysin on membranes involves, or is associated with, the formation of 33 nm rings demonstrable by electron microscopy of negatively stained preparations. 

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