The thermolysis of adamantylideneadamantane dioxetane 1 was investigated. The activation energy for cleavage of 1 was found to be ca. 37 kcal/mol and essentially solvent independent. The thermal decomposition of 1 is chemiluminescent. The yield and nature of the chemically produced excited states were determined by chemical titration and found to be ca. 2% singlet and ca. 15% triplet. Photolysis of 1 leads to the adiabatic formation of singlet and triplet adamantanone with yields of 8 and 40%, respectively. A detailed kinetic analysis of the photochemical reactions of adamantanone with frarw-dicyanoethy-

An effective way of generating student interest in chemical processes is the simple, visual demonstration of unusual chemical phenomena.1 A splendid example is a chemiluminescence reaction. The observation of "cold liquid light" streaming out of a flask is a delight to behold and a fascinating challenge to understand. In nature, many charming examples of chemiluminescence have been noted in the biolumi-nescence2 of the firefly and in luminous bacteria, fungi, deep sea fish, and other species.Chemiluminescence occurs when a sizable fraction of the exothermicity (AH) of a chemical reaction is converted into electronic excitation energy (*) of a reaction product,3 which then emits a photon of light (hv). We can describe chemiluminescence as a AH -* * -*• hv sequence. The heart of the latter is the chemiexcitation (AH -*) step. The * hv process is an ordinary and well-understood luminescence step which serves to announce the presence of an electronically excited state. If we consider photochemistry as a hv -* * -» ' AH sequence, we can imagine that a conceptual link exists between chemiluminescence Nicholas Turro received a B.A. degree from Wesleyan University In 1960, took his Ph.D. from Caltech, did a year's postdoctoral work at Harvard, and then joined the faculty at Columbia, where he is now Professor of Chemistry. He has research interests In many areas, Including work on cyclopropanes and on molecular photochemistry of alkanones In solution, which have been the subjects of previous Accounts. He Is recipient of the 1974 ACS Award in Pure Chemistry sponsored by Alpha Chi Sigma Fraternity and of the 1973 Fresenius Award In Chemistry sponsored by the Psi Lambda Upsilon Fraternity.Peter Lechtken was awarded the Ph.D. by Universitat Erlangen and returned there to join the faculty on completion of a NATO Postdoctoral Fellowship at Columbia In 1972-1973 Schore, who is a postdoctoral fellow at Caltech, received his Ph.D. at Columbia working with Dr. Turro. Gary Schuster's Ph.D. work was done at the University of Rochester. Following a hitch in the Army, Dr. Schuster is doing postdoctoral research at Columbia. Hans-Christian Steinmetzer received the Ph.D. from Universitat Würzburg, did postdoctoral work at Columbia, and is now at Universitat Frankfurt. Ahmad Yekta, who is now on the faculty of Ayra-Mehr University in Tehran, obtained the Ph.D. at Columbia in 1973. phenomena (photochemistry in reverse!) and photochemical reactions.

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(RS)- 6-acetoxl.-5,.6-dimeth?.l-, (RS)-6-ucetoxy-2,4,6-1rimeth~.l-, 3,4,6-tet r m n i 4 i j~l -. and (RS)- 6-oci~tox~-2,3,4,5,6-pentumeth~l-2,4-c~clo/ie.~udii~n-I-oni~.~ serve as representative educts.Thcrc arc two separate main photochemical routes conveniently designated as l(n*, n) or '(n*, n ) tracks. The latter may also he attained by sensitization and leads to phenols. The former, by a-cleavage furnishes dien-ketens as indispensable phototransients. Photolysis of dien-ketens follows one or more of three reaction channels, each of which yields a particular type of photoproduct: heat-induced monocyclization affords 2,4-cyclohexadien-1-ones, heat-induced hicyclization stereoselectively furnishes bicyclo[3.1.0]hex-3-en-2-ones, and multi-step addition of protic nucleophiles stereosclcctively gives l,4-, I,6-and/or 1,2-adducts. By X-ray analysis or NOE studies, the structure of isolated photoproducts is establishcd. Conventional spectroscopy at low or flash spectroscopy at normal temperature yield information on the Cormation and decay of kinetically unstable intermediates. Photoproduct composition depends on the pattern o C substitution of the educts, o n thc solvents, and on the nucleophiles that might he present. Substituents primarily exert an influence upon the population of the various conformers of the dien-ketcn. Solvents affect the rate of the divers reaction paths competing for the phototransient. Nucleophiles play more than a trivial role when adducts are formed. With the detailed view of a dien-keten's role on hand, the photoproduct from a given o-quinol-acetate -or more general from a linear conjugatcd cyclohexadienone -is now predictable.