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. (15[2]-5[1])In one biosynthetic (-5[1])pathway, this phenomenon causes a ring opening in (*) 7-dehydrocholesterol. (10[1]-5[1])This phenomenon (10[1])causes (10[1])the formation of a cyclobutane ring connecting two (10[1])adjacent pyrimidines, creating thymine dimers and thus causing DNA damage. (10[2])This phenomenon causes (10[1])the formation (10[1])of molecular (-5[1])oxygen and oxygen radicals (-5[1])as part of an (10[1])atmospheric cycle that absorbs this phenomenon. (10[1])For 10 points, (10[1])name this component of sunlight used in the biosynthesis of vitamin D. (10[3])■END■ (10[2])