INVESTIGATION OF THE PHOTO-FRIES REARRANGEMENT REACTIONS OF 1-NAPHTHYL AND 2-NAPHTHYL ACETATES

The investigation of the photo-Fries reaction of 1- and 2-naphthyl ace tates (1- and 2-NAs) was performed using stationary photolysis, laser flash photolysis and steady state and time-resolved chemically induced dynamic nuclear polarization (CIDNP). The transient absorption spectr a of the 1- and 2-naphthoxyl radicals and the 1-NA and 2-NA triplet st ates were detected, and the quantum yields and absorption coefficients were obtained. The influence of a triplet quencher on the naphthoxyl radical quantum yield was studied, and the singlet nature of the prima ry radical pair was confirmed for both initial compounds. On laser fla sh photolysis of 1-NA, the formation of the ortho product was directly detected, and the rate constant of the [1,3] hydrogen shift reaction was established. The signs of the CIDNP signals during the photolysis of 2-NA point to a singlet precursor of the radical pair giving rise t o the rearrangement products, and to a tripler precursor for the dispr oportionation products of the parent radical pair. A comparison of the slopes of the Stern-Volmer plots fur the rearrangement product quantu m yield, for triplet CIDNP, and for the optically detected 2-NA triple t state confirms the previously reported assumption about the main rol e of the excited singlet state and the involvement of two different tr ipler states in the reaction. A general kinetic scheme for 1- and 2-NA photolysis is proposed. (C) 1997 Elsevier Science S.A.