Closed-shell compounds electron transfer

On a molar basis, most organic compounds contain similar amounts of hydrogen and carbon, and processes involving transfer of hydrogen between covalently bound sites rank in importance in organic chemistry second only to those involving the carbon-carbon bond itself. Most commonly, hydrogen is transferred as a proton between atoms with available electron pairs (l), i.e. Bronsted acid/base reactions. The alternative closed shell process, hydride transfer or shift, involves motion of a proton with a pair of electrons between electron deficient sites (2). These processes have four and two electrons respectively to distribute over the three atomic centres in their transition structures. It is the latter process, particularly when the heavy atoms are both first row elements, which is the subject of this review. The terms transfer and shift are used here only to differentiate intermolecu-lar and intramolecular reactions. 

The closed-shell system thorium(IV) shows no electron transfer satellites (15). Protactinium is too rare and too radioactive to be measured by us, but certain uranyl compounds such as RbUC>2(02N0)3 show satellites about 3.5 eV above /(IJ4/5/2) and 7(U4/7/2) probably due to electron transfer to the empty 5/ shell. The somewhat peculiar photo-electron spectra of uranium compounds are further discussed Chapter IIF. 

On this basis the strong poisoning effect of certain substances (e.g., of KCN, Na,S, CO in the case of platinum or palladium) can be easily understood it is likely that the metal ions on the surface can form (surface) coordination compounds with these inhibitors, and it is well known that in many of these coordination compounds closed electron shells are present, which, on account of their high ionization potentials would greatly reduce the occurrence of electron transfer processes on the surface which appear to be essential for the catalytic activity of the metal. 

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