Axial groups

The reductions are effected in nature by ferredoxin (p. 1102). This behaviour can be reproduced surprisingly well by simpler, model compounds. Some of the best known of these are obtained by the addition of axial groups to the square-planar complexes of Co with Schiff bases, or substituted glyoximes (giving cobaloximes) as illustrated in Fig. 26.7. The reduced Co species of these, along with vitamin... 

Diaxial interaction (Section 4.8) The strain energy caused by a steric interaction between axial groups three carbon atoms apart in chair cyclohexane. 

The high importance of the steric interaction of the incoming nucleophile with the axial groups at C-3 and C-5 of the cyclohexanone is impressively demonstrated by addition reactions to 3,3,5-trimethylcyclohexanone (14). The presence of an axial methyl substituent intensifies the steric interaction in such a way that the nucleophile is forced to enter the carbonyl group exclusively from the less hindered equatorial side6,7,21. Exclusive formation of the axial... 

The kinetics and mechanism of chloride and bromide substitution of diaquonickel(III) complexes with several ligands of the cyclam type have been studied. The data reveal a reversible process yielding [NiL(H20)X]2+ and are consistent with a dissociative mechanism, sterically more demanding axial groups substantially increasing the rate. In addition, a rearrangement step is observed subsequent to the formation of the monohalide complex.146... 

It should be noted that the patent literature describes a vast number of phthalocyanine derivatives for use as CD-R dyes along the lines already described, with almost every conceivable combination of central metal, axial groups on the central metal, and peripheral substituents on the ligand however, the difference between real and proposed molecules is not obvious, and experimental information and optical performance data is sketchy at best. 

A study of the catalytic oxidation of six stereoisomers of 5-cyclohexene-l,2,3,4-tetrol revealed448 that, in all cases, an allylic hydroxyl group is selectively attacked, and a consideration of their favored conformations suggested that quasi-axial groups are selectively dehydrogenated before those that are quasi-equatorial. 

Poulos et al., 1985,1986), also have a porphyrin-liganding group, but the axial ligands may vary. In catalase the axial groups are water and tyrosine, while in cytochrome P-450 (Fig. 24) they are cysteine and water or oxygen. 

In pyranoses RuO -based reagents oxidise equatorial or axial groups with equal ease [312, 317],... 

The reaction of methyl a-D-mannopyranoside with sulfuryl chloride gave methyl 6-chloro-6-deoxy-a-D-mannopyranoside 2,3,4-tri(chloro-sulfate) even treatment of the product with pyridinium chloride for 12 hours at 50° did not effect further substitution.25 In this case, the lack of displacement of the chlorosulfonyloxy group at C-4 is attributed to the presence of an axial group at C-2. In the (hypothetical) transition state 13 (viewed along the C-4-C-3 bond), there would be... 

In this case, the lack of displacement of the chlorosulfonyloxy group at C-4 is attributed to the presence of an axial group at C-2, and the lack of displacement at C-3 is attributed to the preseuce of the axial methoxyl group at C-l. 

One type of permutational rearrangement, known as pseudorotation, can be visualized as in Eq. 12-28.668 669 The axial groups a and b move back while equatorial groups 2 and 3 move forward, still in the same equato-... 

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