Unsymmetrical photodimerization of a 9-aminomethylanthracene in the crystalline salt.

By the salt formation with particular nonaromatic dicarboxylic acids, rapid and selective photodimerization of 9-(N,N-dimethylaminomethyl)anthracene (1) was accomplished in the solid state. For instance, the salt with trans,trans-muconic acid or acetylenedicarboxylic acid was led quantitatively to the 9,10:4',1' photodimer usy-ht-2, the first example of the unsymmetrical [4+4] photodimerization of anthracene in the solid state. The reactions were rationalized by the relevant C...C distances between the reacting carbons.

Ammonium 4-methoxycinnamate.

In the title compound, NH(4)(+).C(10)H(9)O(3)(-), bimolecular layers of the anions are formed between layers of the cations. There are N-H.O hydrogen bonds between the ammonium ion and the carboxylate groups of the anions. In the crystal structure, the C=C moiety of the cinnamate ion makes an angle of 117.1 (2) degrees with that of the nearest neighbour, indicating that a pedal rotation is required before beta-type [2+2]-photodimerization can take place, which is the predominant mode of the photochemistry of this compound.

Single-crystal-to-single-crystal photodimerization of 4-chlorocinnamoyl-O,O'-dimethyldopamine.

[2+2]Photodimerization of the title compound, C(19)H(20)ClNO(3), has been observed in situ by single-crystal X-ray diffraction. Pairs of monomers related by centers of symmetry have parallel C=C bonds at a C.C distance of 4.155 (17) A. Irradiation of a single crystal with a mercury lamp achieves 100% conversion to the dimer. Redetermination of the structure during the course of the reaction revealed a linear correlation between the percent conversion to the dimer and the decrease in the cell Volume. The displacement parameters for the pure dimer structure are substantially smaller than those for the pure monomer structure. The dimerization reaction is also induced by irradiation with X-rays, the induction being stronger with Cu Kalpha than with Mo Kalpha radiation.