Mechanism of the Photochemical Ring Expansion of N-Vinyl-2-pyrrolidone. Estimation of the Recombination-Time of Biradical

The photochemical ring expansion of N-vinyl-2-pyrrolidone (NVP) has been carried out at 254 nm. The reaction quantum yield depends a great deal on the solvnet viscosity and temperature. The recombination time of the biradical of RP produced by Norrish type I fission was estimated to be ≈10−10 s by application of the Einstein and Smoluchowski-Debye equations. The spin inversion of the biradical in a solvent cage is also discussed according to Kaptein’s theory of the radical-pair mechanism.