The 4,4'-(1,2-ethanediyl)bisbenzyl biradical: its generation, detection, and (photo)chemical behavior in solution

The 4,4'-(1,2-ethanediyl)bisbenzyl biradical (2) is clearly and efficiently generated by photolysis of [3.2]paracyclophane-2-one (8) in cyclohexane solution. This intermediate is also formed via two-photon processes from [2.2]paracyclophane (3) and 1,2-bis(4-chloromethylphenyl)ethane (4). The products arising thermally from biradical 2 are [2.2]paracyclophane and [2.2.2.2]paracyclophane (11) (under high-intensity conditions). Furthermore, two-laser two-color flash photolysis shows that biradical 2 is photostable in solution at room temperature. Thus, formation of p-xylylene (1) from 2 occurs neither thermally nor photochemically.