Results of ab initio calculations comparing the 1,3-cycloadditions of ozone to ethylene, benzene, and phenol are presented. The potential energy surfaces of these reactions are explored to establish structures and relative energies of transition states and addition products. Calculations are performed at the B3LYP level for geometry optimizations and at the CCSD(T)/6-31G(d,p) level for energetics. For the ethylene reaction the calculated activation barrier and exothermicity correspond within a few kilocalories per mole with previous theoretical studies and experimental data, rendering credit to the computational model used. Calculations for the benzene ozonolysis yield a barrier of 15.8 kcal/mol that corresponds quite well with the experimental value of 14.6 kcal/mol. The phenol reaction is predicted to possess a barrier of 9.5 kcal/mol. The most stable primary ozonides of benzene and phenol are calculated at 18.9 and 29.0 kcal/mol below the corresponding entrance channels, respectively. In the specific case of the phenol ozonide, the most stable conformation for this intermediate is compatible with the experimentally determined initial reaction product catechol. The carbon rings in the primary ozonides of benzene and phenol are found to retain their planarity.