Geometry optimizations for 11 1,2-disubstituted-2,3-epoxy-cyclopentanol diastereomers were studied using the M06-2X/cc-pVTZ method and basis set to probe mechanistic details in the alpha-epoxy alcohol semipinacol rearrangement reaction. Electronic energies of active cis diastereomers are on average 0.9 kcal mol(-1) lower than trans diastereomers. Intramolecular hydrogen bonding stabilizes the cis substrate energy by 3.4 kcal mol(-1), on average.