Heating of 3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-D-arabino-hex-1-enitol (per-O-acetyl-D-glucal) in water leads to a mixture of unsaturated compounds with cyclic as well as open-chain structures. The mixture obtained was analyzed by the CGC method. The experimental findings were employed to model the mechanism of the transformation studied. In addition, AM1 calculations were carried out in order to describe the elementary processes suggested. Full geometry optimizations performed for species found in the mixture made it possible to evaluate the thermodynamic characteristics of particular reactions. Next, the calculations for transition states afforded appropriate kinetic barriers. All computations were carried out for a gaseous phase as well as an aqueous solution. Both experimental and theoretical results conform well with the mechanism proposed.