Closed-shell compounds

Initiations Radicals from Closed-Shell Compounds. 140... 

Termination reactions convert radicals to closed-shell compounds. Radical-radical coupling reactions are the reverse of homolytic cleavage reactions and are common, but radicals with (3-hydrogen atoms also react in disproportionation reactions as shown for 13. The selectivity of radical-radical terminations is low because the... 

The cage effect can be a source of great frustration in matrix isolation studies of monoradicals, because such species are usually formed by homolysis from closed-shell compounds, and hence any radical generated in situ is invariably accompanied by another radical that will be trapped in the same matrix cage. 

In early studies, flash vacuum pyrolysis, a method that has proven very valuable in preparative studies of closed-shell compounds,was regarded as the method of choice for the production of radicals for matrix isolation studies. " The disadvantage of this method, which is very well suited for preparative studies of closed-shell compounds, is that the reaction occurs on the walls of a hot tube whose surface may trap radicals (this problem may be alleviated by coating the inside of the tube with gold ). Also, unless a very low vacuum can be maintained in the pyrolysis mbe, collisions between radicals may lead to gas-phase dimerization. 

Carbon and hydrogen have always been considered as two basic and mandatory elements of organic compounds. Recent discoveries in the area of caged structures, however, reveal that a whole family of closed shell compounds composed of pure carbon with the general empirical formula C should be included as well in the list of objects to be studied by organic chemistry. At present, only two individual compounds, 59 (Cso) and 60 (C70) (Scheme 4.18), have been prepared and unequivocally identified. 

The structures within the homologous series Gdj + 2 2n + 3 C have been described in sect. 2 as a ccp arrangement of X and C atoms with Gd atoms in of the octahedral holes, i.e. as ordered defect derivatives of rock salt. That closed-shell situations do not always maximize stability is excellently demonstrated for the w = 1 and n = 2 members of the series because removal of one Gd atom per formula unit would produce closed-shell compounds in each case, Gd3X5C and Gd5X7C2 . Both metal-metal bonding interactions introduced by the three conduction electrons as well as the requirements of the highly charged interstitial atom to have a spherical shell of... 

It should be remembered that it is a radical species that results from the addition of muonium to the close-shell compound that is studied in xSR. In studies of molecular, whole body dynamics where the muon appears to be an almost passive observer, it is the very light mass of the muon that makes possible for the observation of properties which are almost identical to those of the parent molecule. There are a number of such studies of organic systems [1]. jlSR studies of the dynamics of fullerenes Ceo and C70 are particularly interesting examples of such whole body motions where the change in the moment of inertia because of the added muonium is neglegible [27,28]. However the use of jlSR to study intramolecular dynamics presents at least two distinct scenarios. 

Awaga, K., Sugano, T., and Kinoshita, M., Ferromagnetic intermolecular interactions in a series of organic mixed-crystals of galvinoxyl radical and its precursory closed shell compound, J. Chem. Phys., 85, 2211, 1986. 

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