N. C. and D.-D. H. Yang discovered a reaction in which this phenomenon causes C-H functionalization. Promoting reactions involving this phenomenon is the typical use of benzophenone. The first organic reaction known to involve this phenomenon is the rearrangement of santonin. This phenomenon cleaves a carbonyl in the usual forms of both types of Norrish (-5[1])reactions. In one biosynthetic pathway, this phenomenon causes a ring opening in (*) 7-dehydrocholesterol. This phenomenon causes the formation of a cyclobutane ring connecting two adjacent pyrimidines, creating thymine dimers and thus causing DNA damage. This phenomenon causes (10[1])the formation of molecular oxygen and oxygen radicals as part of an atmospheric cycle that absorbs this phenomenon. For 10 points, name this component of sunlight used in the biosynthesis of vitamin D. (10[1])■END■