AN EPR STUDY OF THE ALKYLHYDRAZYL RADICALS FORMED AT ROOM-TEMPERATUREIN THE PHOTOCHEMICAL-REACTION OF 2,2'-AZOBIS(2,4-DIMETHYLVALERONITRILE) OR 2,2'-AZOBIS(PROPANE-2-CARBOXAMIDINE) DIHYDROCHLORIDE IN THE PRESENCE OF SENSITIZERS

Alkylhydrazyl radicals R-NH-N-R are formed in the photochemical reacti on of 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN) and 2,2'-azobis(pr opane-2-carboxamidine) dihydrochloride (APCH) in methanol in the prese nce of sensitizers such as p-hydroquinone. The radicals from AMVN exhi bited a nine-line EPR spectrum due to interaction with two non-equival ent N-14 nuclei (a(N1) = 1.22 mT; a(N2) = 0.854 mT; g = 2.0038). The r adicals from APCH exhibited an 18-line spectrum by interaction with tw o non-equivalent N-14 nuclei and one hydrogen nucleus (a(N1) = 1.20 mT ; a(N2) = 0.83 mT; a(H) = 0.21 mT). The addition of HCl changed the sp ectra to five-line-patterns. indicating an interaction with two equiva lent N-14 nuclei (a(N) = 1.04 mT). At the same time. the doublet split ting of the spectrum of APCH disappeared. The reactions involve an equ ilibrium between two identical states I and II. [GRAPHICS] As long as the interconversion is slow, the spectrometer shows two non-equivalent N-14 nuclei. When the exchange rate is increased (acid), the two N-14 nuclei are registered as equivalent. The sensitization is believed to involve a one-electron transfer to the azo compounds from an excited state of the sensitizer, followed by the addition of a proton to the a zo anion radical.