Study of the oxidative degradation of 2,2,3,4,5-pentaphenyl-3- cyclopentenone by various oxidants ; and, [1,5]-sigmatropic phenyl rearrangements in 2- and/or 5-(p- or m-substituted phenyl)-1,3,4-triphenyl-2,4- cyclopentadien-1-ols : electronic effects at the migration terminus