The mechanism of the [2,3] allyl hydroperoxide rearrangement was investigated. The rearrangement proceeds with stereoselectivity and is promoted by free radical initiators. Recent theoretical investigations by Boyd et. al. support a beta-fragmentation process involving an intermediate allyl radical for this rearrangement, and this mechanism was probed using solvent viscosity, isotopic labeling, and stereochemistry. These studies indicate that solvent viscosity and temperature affect the partitioning between escape and collapse of an intermediate allyl radical-dioxygen caged pair and support the dissociative mechanism. An increase in solvent viscosity results in a decrease in escape product and an identical increase in pair collapse product formed with stereocontrol.