The steric effects of allylic substituents in the epoxidations bonding is ineffective and steric interactions cause a higher trans selectivity. The conformationally fixed cis-and trans-with methyltrioxorhenium/urea/hydrogen peroxide adduct (MTO/UHP) have been assessed for a series of 3-alkyl-5-tert-butyl-2-cyclohexenols serve as suitable substrates for gauging the dihedral angle of the transition states for the substituted cyclohexenes. The trans selectivity increases with the size of the substituent and the diastereoselectivities oxygen transfer in these epoxidations. Thus, the MTO/UHP oxidant favours a quasi-equatorial arrangement of the follow an excellent linear correlation with the steric substituent constants of Taft (E s ) or Charton (ν). Good cis hydroxy group for effective hydrogen bonding (hydroxygroup directivity), in analogy to m-chloroperbenzoic acid (m-selectivity is observed in the epoxidation of the cyclic allylic alcohols 2-cyclopentenol and 2-cyclohexenol due to a CPBA) and dimethyldioxirane (DMD), and a dihedral angle of ca. 130°is suggested. hydroxy-directing effect through hydrogen bonding; however, for 2-cycloheptenol and 2-cyclooctenol hydrogen dant may be estimated. The VO(acac) 2 -catalysed epoxi-Am Hubland, D-97074 Würzburg, Germany 1) or the Charton steric parameter ν [11] (data not shown),