Protonation of bridge

On the other hand, the bands at 490 and 570 nm can be attributed to the radiative decay process of two types of photoexcited Cu(I) ion, a and // respectively, formed upon reduction of Cu(II) ions introduced by exchange of the protons of bridging hydroxyl groups (Si-OH-Al). Cu(I) ions of type j> are assumed to be coordinated by -Si0(A10P0A10) Si-groups with relatively large values of n as compared to Cu(I) ions of type a. 

Protonation of bridging CH, groups in diruthenium complexes proceeds ... 

Complex 1 is formed very rapidly in solution, second-order rate constant > I0 M sec at 5°, which may partly result from the supposed structure of Co(CN)5 in that no solvent has to be displaced by entering O2 (54). The oxygenation may be irreversible since Co(CN)5 does not appear on subjecting oxygenated solution to a vacuum 41). The adduct is only stable in high alkalinity >IM OH" 41), it has pK 12 ascribed to protonation of bridged O2 (42) but this may indicate the latter is O... 

Negative framework charges of zeolites, due to tetrahedrally coordinated aluminum atoms, are either compensated by hydroxyl protons of bridging OH groups or by exchangeable univalent or multivalent extra-framework cations. In... 

In some cases, reactions of oxo compounds with mineral acids generate water and the metal halide (Equation 13.85). Similarly, reactions of imido complexes with mineral adds often generate amine and the metal dihalide (Equation 13.86). The rate of protonation of metal-oxo complexes has been studied. The rate of protonation of bridging oxo compounds can be slow, but the rate of protonation of a terminal oxo species is presiunably faster. 

As with AI(BH4)3 and related compounds (p. 230), solutions of AbMe6 show only one proton ninr signal at room temperature due to the rapid interchange of bridging and terminal Me groups at —75° this process is sufficiently slow for separate resonances to be observed. 

Rauscher 42 calculated that the protonation of a double bond (Eq. (2)) leads to nonclassical, that means H-bridged, cations if the double bond is substituted symmetrically (Rj = R and Rj = R ). 

An early process in the cure reaction is protonation of a methylolphenol, followed by loss of a molecule of water to produce a benzylic carbonium ion (see reaction 4.3). This may be followed by reaction with a second phenol to generate a bridged structure, as illustrated in Reaction 4.4. Alternatively the... 

Thus, l,6-methano[10]annulene (77) and its oxygen and nitrogen analogs 78 and 79 have been prepared and are stable compounds that undergo aromatic substitution and are diatropic. For example, the perimeter protons of 77 are found at 6.9-7.3 5, while the bridge protons are at —0.5 5. The crystal structure of 77 shows that the perimeter is nonplanar, but the bond distances are in the range 1.37-1.42A. It has therefore been amply demonstrated that a closed loop of 10 electrons is an aromatic system, although some molecules that could conceivably have such a system are too distorted from planarity to be aromatic. A small distortion from planarity (as in 77) does not prevent aromaticity, at least in part because the s orbitals so distort themselves as to maximize the favorable (parallel) overlap of p... 

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