TheCâO homolytic bond dissociation enthalpies(BDEs) werecalculated by high-level ab initio including G4, G3B3, G3, CBS-QB3and a series of density function theory (DFT) methods. It is foundthat the wB97 method gave the most reliable CâO BDEs and theroot-mean-square deviation (RMSD) is 7.6 kJ/mol. Therefore, the C(sp2)-O BDE predictions and the substituent effects of alkenylphosphates/sulfonates and aryl phosphates/sulfonates were investigatedin detail by using the wB97 method. Interestingly, there exist differentsubstituent effects in α- and β-substituted alkenyl phosphates/sulfonates.Excellent linear relationships between the CâO BDEs of β-substitutedalkenyl phosphates/sulfonates with substituent constant Ïp쇪 found. In addition, the NBO analysis furtherdisclosed the essence of the substituent effects on CâO BDEs. [ABSTRACT FROM AUTHOR]