Reactions of polyarylated carbinols. 6. Kinetics of the thermal [1,5] sigmatropic phenyl and para-substituted-phenyl rearrangements in 3,4-bis[p-substituted-phenyl]-1,2,5-triphenyl-2,4-cyclopentadien-1-ols and 1-[p-substituted-phenyl]-2,3,4,5-tetraphenyl-2,4-cyclopentadien-1-ols