The history of ozone. Part VIII. Photochemical formation of ozone.

The historical development of the photochemical formation of ozone in the atmosphere is outlined, starting from the discovery of ozone by Schönbein in 1843 and the postulation of its role as UV filter by Hartley in 1881.

Quantum yield: the term and the symbol. A historical search.

Einstein's Photochemical Equivalence Law, i.e. one quantum of light absorbed per molecule, played a very important role in the development of photochemistry in the early part of the 20th century. The corresponding terminology, quantum yield and its symbol Phi, became accepted usage in a haphazard manner, which is presented in this paper.

Photochemistry of Diaryl Vicinal Tetraketones and Chemistry of Intermediate (Aroyloxy)arylketenes(1).

Photolysis of diaryl vic-tetraketones results in formation of tricyclic-gamma-lactones 3 and 4 with low quantum but high chemical yield. (Aroyloxy)arylketenes and carbon monoxide are the initial photochemical products of these photolyses. Subsequent reaction of ketene with ground-state tetraketone results in formation of the observed photoproducts via intermediate beta-lactones. The latter are formed with a high degree of stereoselectivity. The failure of a cyclic tetraketone to react is attributed to its inability to undergo the cyclic mechanism proposed for formation of ketenes from tetraketones. Dimesityl and di-tert-butyl tetraketones react by a competing intramolecular hydrogen atom transfer mechanism. Dimerization of (benzoyloxy)phenylketene and its reactions with a number of tetraketones are described.