TIME-RESOLVED STUDIES OF THE PHOTOGENERATION AND PHOTOCHEMISTRY OF TETRAMETHYL-ORTHO-XYLYLENE

The photodecomposition of 1,1,3,3-tetramethyl-2-indanone (V) leads to the formation of tetramethyl-o-xylylene (III), which ultimately decays to give o-isopropenylcumene (IV) as the only product. The xylylene III shows λmax~358 nm in benzene and has a remarkably long lifetime, 9.1 min at room temperature. The infrared spectrum of III was recorded in situ at room temperature (in cyclohexane or carbon tetrachloride); characteristic bands were observed at 681 and 1212 cm-1. Laser photolysis studies reveal that the formation of III involves an intermediate with a lifetime of 580 ns, which is attributed to the 1,4-biradical VI; this species is the same as the triplet state of III, and is readily scavenged by oxygen and β-carotene. Two-laser two-color experiments indicate that the photolysis of III yields the same product as its thermal decay (i.e., IV), but the photochemical process is at least 10 orders of magnitude faster than the thermal reaction. © 1990, American Chemical Society. All rights reserved.