Molecule, acetone naphthalene

One example of an aromatic molecule with markedly different singlet and triplet-state photochemistry is provided by [2.2]paracyclo-phane.203 Irradiation at wavelengths above 2700 A or photosensitization with acetone yields p-ethylbibenzyl as the sole product. This must be a triplet product because the reaction is quenched by naphthalene. Direct irradiation of the paracyclophane at 2537 A and lower wavelengths produces other products. 

Perkey and Farhataziz [38] have measured the rate constants for the reaction of e am with some aromatic hydrocarbons (anthracene, nitrobenzene, phenan-threne, naphthalene, benzamide), with acetone and with dichloromethane, 1,2-dichloroethane, and 1-chloropropane. In the case of the aromatic molecules listed above, the rate constants are an order of magnitude larger than the corresponding values in water, reflecting the lower viscosity of liquid ammonia and indicating that the reactions are diffusion-controlled. In the case of biphenyl (B), the reaction of e am was found to be reversible [39] ... 

Absolute rate constants have been determined for aromatic triplet formation in acetone solutions of several aromatic compounds (5, 30). The formation curves were observed directly for anthracene and naphthalene triplet (5) and for diphenyl triplet. These rate curves were found to fit a first order rate law, and were interpreted as a bimolecular energy transfer process from a state of the solvent molecule which is probably the triplet, that is, by Reaction 11. These rate constants, as well as the triplet yields, are listed in Table VI. The rate constants for anthracene and naphthalene triplet formation appear to correspond to diffusion controlled rate constants. Two further points are of interest, which are in contrast with observations in other systems which will be discussed. In acetone, most of the yield of aromatic triplet (at concentrations of the aromatic compound of 5 X 10"3M or lower) is formed in diffusional processes such as collisional energy transfer. Any fast formation appears... 

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