Terminal oxygen atom of the

Figure 2.21. Changes in (a) total energy and (b) partial charge on the terminal oxygen atoms of the NO ligands, calculated for the stepwise decrease of the 0—0 distance in the attracto conformation of the copper(I) dinitrosyl complex (after [75]).

Stereospecific action of the alkoxyaluminum compound was interpreted by Natta independently (24). They proposed the coordinate anionic mechanism, and suggested that an aluminum atom forms a complex with an oxygen atom immediately preceding the terminal oxygen atom of the growing chain. An activated complex thus formed has a steric configuration which permits the minimum nonbonded... 

Vogl and Bryant (25) suggested a similar mechanism in which four oxygen atoms are coordinated to a metal atom. In addition to the terminal oxygen atom of the growing chain, two monomer molecules and the penultimate monomeric unit supply oxygen atoms required for the coordination. Simultaneous coordination of two molecules of aldehyde prior to addition may justify the observed sequence of iso-... 

The reaction of SO2 with rf dioxygen complexes gives a chelated sulphate complex. Isotopic labelling studies with 62 show that one of the terminal oxygen atoms of the sulphate originates from the dioxygen complex and the other from the SO2. This has been interpreted in terms of the rearrangement of a five membered cyclic intermediate . ... 

Fig. 4.2 The (100) surface of quartz. The X s mark the terminal oxygen atoms of the SiO structure. The unit cell is rectangular (achiral), but its atomic structure clearly lacks mirror symmetry rendering it chiral...

The Prilezhaev reaction is stereospecific, and a syn addition of the oxygen to the double bond is observed in all cases. This observation supports the assumption that the epoxidation of alkenes by peroxyacids is a concerted process. The reaction takes place at the terminal oxygen atom of the peroxyacid, and the n HOMO of the olefin approaches the o LUMO of the 0-0 bond at an angle of 180° (butterfly transition structure). 

The foregoing brief description of the catalytic properties, and physical, structural and surface chemistry of heteropoly oxometalates demonstrates the multifunctional capabilities of these solids in various processes. While in some respects similar in their properties and behaviour to zeolites some notable differences are evident. The properties of heteropoly oxometalates evidently depend predominantly but not entirely on the nature of the central and peripheral metal elements of the anion, but the contribution of the cation cannot be neglected. Nevertheless, there is convincing evidence that the terminal oxygen atoms of the anion play a central role in the mechanism of any catalytic process in which heteropoly oxometalates participate, and in particular in the conversion of methanol to hydrocarbons and the partial oxidation of methane. 

Figure 4.6. Schematic representation of the dinuclcar complex (U02)2(M-2 OH)2Cl2(H20)4 including proposed hydrogen bonds A, B, C, D, E and F in the crystal. Top view (left) and side-view (right). The terminal oxygen atoms of the uranyl units are not shown in the top view. Italics indicate frontier groups of neighboring complexes in the crystal.

The cations and the silicate anions are attached to each other with a system of hydrogen bonds formed by the water molecules. Each terminal oxygen atom of the ring is bonded to three water molecules. The chelate complex is included in the system of hydrogen bonds through the UHp- groups ( ). 

The catalytic cycle of TauD has been studied extensively 20-22) and is schematically depicted in Fig. 2 starting fix)m the aKG-bound structure (A). When taurine enters the substrate binding pocket the last water ligand of the metal is released (structure B) prior to dioxygen binding (structure C). The terminal oxygen atom of the iron(III)-superoxo structure subsequently attacks the a-keto... 

Therefore 0(11) was considered to belong to the second shell this is supported by its function as the bridging oxygen in a double tetrahedron with a reduced charge contribution as compared with the terminal oxygen atoms of the polyhedron. The arrangement of the closest seven oxygen atoms at a mean distance of 2.48 A of the first shell of Pr(l)... 

When one of the Py or p atomic orbitals on the terminal oxygen atom of the Fe -02 increased-valence structme (38) overlaps with the N-H hydrogen atomic orbital of the distal histidine, a (weak H-0) 6-electron 5-centre bonding unit is established, as in stractme (48) (49). 

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