SUBSTITUENT EFFECTS IN DI-PI-METHANE REARRANGEMENT OF 1,1-DICYANO-2-METHYL-3-PHENYLPROPENE

1,1-Dicyano-2-methyl-3-phenylpropene and ring-substituted derivatives on photolysis undergo a di-π-methane rearrangement to give the corresponding cyclopropane derivatives. The effect of ring substitution on the quantum yields of these singlet state reactions can be analysed in terms of the balance between diradical and charge-transfer character on initial bonding. If the extent of charge transfer is large, efficient non-radiative relaxation of the ' zwitterion ' to the ground state olefin takes place, resulting in low quantum yields for the di-π-methane rearrangement.