Olefin bonds photoreactive molecules

In order to rationalize such characteristic kinetic behaviour of the topochemical photoreaction, a reaction model has been proposed for constant photoirradiation conditions (Hasegawa and Shiba, 1982). In such conditions the reaction rate is assumed to be dependent solely on the thermal motion of the molecules and to be determined by the potential deviation of two olefin bonds from the optimal positions for the reaction. The distribution of the potential deviation of two olefin bonds from the most stable positions in the crystal at OK is assumed to follow a normal distribution. The reaction probability, which is assumed to be proportional to the rate constant, of a unidimensional model is illustrated as the area under the curve for temperature Tj between 8 and S -I- W in Fig. 7. 

A great number of olefinic compounds are known to photodimerize in the crystalline state (1,2). Formation of a-truxillic and / -truxinic acids from two types of cinnamic acid crystals was interpreted by Bernstein and Quimby in 1943 to be a crystal lattice controlled reaction (5). In 1964 their hypothesis on cinnamic acid crystals was visualized by Schmidt and co-workers, who correlated the crystal structure of several olefin derivatives with photoreactivity and configuration of the products (4). In these olefinic crystals the potentially reactive double bonds are oriented in parallel to each other and are separated by approximately 4 A, favorable for [2+2] cycloaddition with minimal atomic and molecular motion. In general, the environment of olefinic double bonds in these crystals conforms to one of three principal types (a) the -type crystal, in which the double bonds of neighboring molecules make contact at a distance of -3.7 A across a center of symmetry to give a centrosymmetric dimer (1-dimer) (b) the / -type crystal, characterized by a lattice having one axial length of... 

In general, photoinert auxiliary molecules have been used as templating agents to direct double bonds in parallel orientations of single olefins and with distances smaller than 4.2 A. These geometrical parameters are strictly required as previous steps in order to achieve the photoreaction via topochemical control and then the template must be liberated from the expected product. We envisage that an alternative way to increase the level of sophistication in the design of solid state reactions is the possibility to extend the self-assembly of two or more potentially reactive unsaturated molecules controlled by directional supramolecular synthons. 

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