different substituents at the aryl ring. The obtained results support the competence of a concerted anionic intramolecular addition/elimination sequence and a radical dissociation/recombination sequence for explaining the tendency of migration for aryl groups. The more favored rearrangements are found for substrates with electron‐poor aryl groups that favor the anionic pathway.
The invention relates to racemates of the formula (I) ##SPC1## in which R.sub.1 and R.sub.2 are hydrogen, lower alkyl, methoxy, ethoxy or halogen, R.sub.3 is unsubstituted alkyl or lower alkyl substituted with alkoxy carbonyl carbonamido, cyano or hydroxyl or unsubstituted alkenyl or alkenyl substituted with halogen or halogen-, methyl-, ethyl-, methoxy- or ethoxy-substituted phenyl or unsubstituted cycloalkyl or cycloalkyl substituted with lower alkyl or unsubstituted phenylalkyl or phenylalkyl, the phenyl nucleus of which being substituted with methyl, methoxy, halogen or nitro, and R.sub.4 is unsubstituted alkyl or alkenyl or unsubstituted cycloalkyl or cycloalkyl substituted with lower alkyl or unsubstituted phenyl or phenyl substituted with lower alkyl methoxy, ethoxy or halogen or unsubstituted phenylalkyl or phenylalkyl, the phenyl nucleus of which being substituted with methyl, methoxy or halogen and X is oxygen or sulphur, Which are useful as photosensitizers for light induced polymerisations of vinyl monomers as well as for the light induced crosslinking of unsaturated polycondensates and polymers.