Reaction cavity alkanones

Reaction cavities of alkanones in neat solid phases 173... 

Reaction Cavities of Alkanones in Neat Solid Phases. The early report that irradiation of crystalline 7-tridecanone at 10°C does not result in discernible photoreaction [267] has been corroborated subsequently with other solid symmetrical n-alkanones [268]. However, careful scrutiny of the irradiated ketone reveals traces of Norrish II products in ratios which are very close to those found from photoreactions in solution. On this basis, it was concluded that the source of the photoproducts is reactions occurring at crystal defect sites. 

As discerned from Table 9, the photoproduct ratios from irradiation of neat 77 vary drastically among homologues and with temperature for the n = 7 member, Unlike the n-alkanones discussed previously, the cyclic diones must be intrinsically bent as shown in the ORTEP drawings in Figure 43. Since the C=0- H, distance in each case is <3.0 A, excitation of the molecules should result in formation of hydroxy-1,4-biradicals. The fate of those radicals depends upon the flexibility of the reaction cavity and its free volume. The results indicate that sufficient free volume is present in the reaction cavities to allow topochemical conversion to photoproducts, but not... 

Closer examination of the cyclobutanol t/c ratios from homologous and isomeric n-alkanones in the same zeolites reveals some interesting trends (Table 12). The t/c ratios from all of the alkanones in the Na-X and Na-Y zeolites are as expected from reaction in a large or flexible reaction cavity which is very polar (like that provided by an alcohol solution). The t/c ratios in the ZSM zeolites indicate that selectivity depends upon the total ketone length and the position of the odd electron centers of the BR along the chain. Ratios of 60 or more are reported from 4-alkanones with 9 or more carbon atoms the t/c ratios from 4-octanone in ZSM-5 and ZSM-11, 15 and 18 respectively, mark 8 carbon atom chains as being critical to a c-BR occupying... 

Exploration of the modes of solubilization of 2- and s-105 in the solid phases of C21 has led to many unexpected and complicating observations [321], First and foremost among these is that only guest alkanone molecules whose lengths are very near that of C21 can be incorporated isomorphously into its solid phases. Thus, C21 is a much more demanding host matrix than BS the dimensions and free volume content of the reaction cavities it provides have a very narrow distribution and their walls are probably less flexible than those in many neat crystals. 

The Norrish type II reaction of various phenyl alkanones in zeohtes has been studied by Ramamurthy and his collaborators. " The size and shape of zeohte reaction cavities control the behavior of triplet ketone as well as the 1,4-biradical intermediate that is consequently monitored as a difference in photoproduct distribution and triplet lifetimes. Norrish type I and type II reactions of 2-pentanone included within cavities of various types of zeohtes and the alkah metal cation-exchanged ZSM-5 zeolite have been investigated by experimental and theoretical approaches. " Ion-exchanged cations had significant effects not only on the adsorption state but also on the photochemical reactions of the ketone. The... 

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