MAGNETIC-FIELD EFFECTS UPON PHOTOCHEMISTRY OF BIFUNCTIONAL CHAIN MOLECULES

External magnetic field effects are discussed for three typical exampl es of photoreactions involving biradical intermediates: photo-induced intramolecular electron transfer in chain molecules D-(CH2)n-A consist ing of an electron donor (D) and an acceptor (A), intramolecular hydro gen abstraction in bifunctional species :X-(CH2)n-YH containing a hydr ogen donor (YH) and an acceptor (:X in the excited triplet state) and photochemical homolytic ring opening of a cyclic ketone which yields a biradical consisting of an acyl and an alkyl group. There has been pr ogress in the elucidation of reaction mechanisms through the analysis of magnetic field effects on lifetimes of reaction intermediates and p roduct yields in radical reactions involving biradicals. Extremely sma ll interactions such as the Zeeman energy and hyperfine interaction ma y give rise to a large change in the distribution of photo-products de rived from bifunctional chain molecules.