Hydroxyl groups in the simple cyclic sugar beta-D-glucose are key to its formation of bicyclic levoglucosan, whether by unimolecular reaction or by catalysis through external hydroxyls or acid molecules. Computational-quantum chemistry calculations of transition states are conducted with substitutions of NH2 and CH3 for OH, which reveal the role of lone pairs on the oxygen; with explicit water molecules or implicit water-solvation models, which show the mixed impact of hydrogen bonding; and with Bronsted acid molecules, which relate acid strength to decreased enthalpy of activation. (C) 2015 Elsevier B.V. All rights reserved.