A study was made concerning the effect of substituants at0-3,0-4 and0-6 ofd-galactal andd-glucal (1, 5-anhydro-2-deoxy-d-lyxo- and -d-arabino-hex-1-enitol, respectively) on the double bond reactivity in the chloroazide addition reaction. Results from the quantum chemical calculations of the model structures (ab initio) and also of the whole cyclic molecules in the half-chair conformation (MINDO-3) together with the reaction indices of olefin carbon atoms are presented. These studies snow that (1) the double bond reactivity and the chloroazide addition mechanism are only affected by the substituent at0-3; (2) the influence of the acyl group is only due to its inductive effect; (3) no interaction between the acyl and the olefin fragments through space was detected. Three0-acetyl-di-0-benzyl-d-galactals were synthesized.