X-RAY STRUCTURES OF 2 PHOTODIMERS OF 2-METHYL-1,4-NAPHTHOQUINONE (MENADIONE)

The structures of the photodimers(I) and (II) of menadione (2-methyl-1 ,4-naphthoquinone, MNQ) mere determined by X-ray analysis. It was conf irmed that both dimers are structural isomers of the cis-syn and cis-a nti forms, i.e., 5a,5b-cis-dimethyl (I) and 5a,11a-cis-dimethyl (II) i somers of ro-beta,beta'-cis-binaphthylene-5,6,11,12-tetrone. The dimer (II), which was twisted around the cyclobutane ring, was more deforme d than the dimer (I). MM2 calculation indicated that such twisting dec reases the steric energy of the dimer (II) more than that of the dimer (I).