The β-scission (reverse reaction of radical addition to multiple bond) of tertbutoxyl radicals was investigated by Weber and Fischer using electron spin resonance to measure rates. They found that at 300 K, the rates in solution were at least ten times larger than the gas phase rates. This result was explained by a transition state effect, where the transition state is more polar than the radical and is thus more stabilized by interactions with polar and polarizable solvents. Furthermore, the β-scission of cumyloxyl radicals measured using laser flash photolysis also showed a rate increase with increasing solvent polarity . The same effect was found for alkyloxyl radicals . Bietti et al. also confirmed this effect and found that the solvent Dimroth-Reichardt parameter (E T ) correlated well with the increase in rate , confirming earlier results by the Ingold group , see Figure .