Facial sites

The structure of the l,2,3,6-f/4-OFCOT complex 64 is shown in Fig. 6 (140). The coordination geometry around iron can be considered as octahedral, with the allylic portion of the OFCOT ligand and the Fe—C a bond occupying three facial sites. The formal oxidation of the metal center is reflected in the higher values of the CO stretching frequencies (vco = 2105, 2060 cm-1) for complex 64 compared to those for the l-4-r/4-COT complex 63 (vco = 2051, 1992, 1978 cm-1) (139). 

Figure 7-26. The structure of complexes may be dictated by steric constraints within the ligands. 2,2 6, 2"-Terpyridine (7.42) can only occupy the three meridional sites in an octahedral complex, whereas the /ra(pyrazolyl)borate anion (7.43) must occupy three facial sites.

HSV is divided into HSV-1, which causes oral, ocular, or facial infections, and HSV-2, which causes genital infection. However, either type can cause disease at either body site. HSV-1 causes painful vesicular lesions in the oral mucosa, face, or around the eyes. HSV-2 or genital herpes... 

The orbital mixing theory was developed by Inagaki and Fukui [1] to predict the direction of nonequivalent orbital extension of plane-asymmetric olefins and to understand the n facial selectivity. The orbital mixing rules were successfully apphed to understand diverse chemical phenomena [2] and to design n facial selective Diels-Alder reactions [28-34], The applications to the n facial selectivities of Diels-Alder reactions are reviewed by Ishida and Inagaki elesewhere in this volume. Ohwada [26, 27, 35, 36] proposed that the orbital phase relation between the reaction sites and the groups in their environment could control the n facial selectivities and review the orbital phase environments and the selectivities elsewhere in this volume. Here, we review applications of the orbital mixing rules to the n facial selectivities of reactions other than the Diels-Alder reactions. 

Summary of the Relationship between Diastereoselectivity and the Transition Structure. In this section we considered simple diastereoselection in aldol reactions of ketone enolates. Numerous observations on the reactions of enolates of ketones and related compounds are consistent with the general concept of a chairlike TS.35 These reactions show a consistent E - anti Z - syn relationship. Noncyclic TSs have more variable diastereoselectivity. The prediction or interpretation of the specific ratio of syn and anti product from any given reaction requires assessment of several variables (1) What is the stereochemical composition of the enolate (2) Does the Lewis acid promote tight coordination with both the carbonyl and enolate oxygen atoms and thereby favor a cyclic TS (3) Does the TS have a chairlike conformation (4) Are there additional Lewis base coordination sites in either reactant that can lead to reaction through a chelated TS Another factor comes into play if either the aldehyde or the enolate, or both, are chiral. In that case, facial selectivity becomes an issue and this is considered in Section 2.1.5. 

Bis(pyrazolylethyl)ether derivatives (106) have been coordinated to zinc providing an N20 donor set. The structural data shows that the ligand coordinates in a meridional rather than facial geometry limiting the application for the modeling of N20 zinc enzyme sites, (derivatives R = i-Pr or Me).161... 

If you are in an area that has a lot of hexachloroethane vapor, your facial muscles may twitch or you may have difficulty moving. These effects have been observed in animals during exposure at levels far greater than those found in industrial use of hexachloroethane or those which would be expected in areas near a hazardous waste site. 

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