N. C. and D.-D. H. Yang discovered a reaction in which this phenomenon causes C-H functionalization. Reactions involving this phenomenon are often promoted by adding a catalytic amount of benzophenone. The first organic reaction known to involve this phenomenon is the rearrangement of santonin. This phenomenon cleaves a carbonyl in both types of Norrish reactions. (15[1])In one biosynthetic pathway, this phenomenon causes a ring opening in (*) 7-dehydrocholesterol. This (10[1])phenomenon causes the formation of a cyclobutane ring connecting two adjacent pyrimidines, creating thymine dimers and consequently causing DNA damage. This phenomenon causes 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 (10[1])used in the biosynthesis of vitamin D. ■END■